TI1 BQ25708 Smbus multi-chemistry battery buck-boost charge controller with system power monitor and processor hot monitor Datasheet

Product
Folder
Order
Now
Support &
Community
Tools &
Software
Technical
Documents
bq25708
SLUSCU2 – NOVEMBER 2017
bq25708 SMBus Multi-Chemistry Battery Buck-Boost Charge Controller With System
Power Monitor and Processor Hot Monitor
•
•
•
•
•
•
•
•
Charge 1- to 4-Cell Battery From Wide Range of
Input Sources
– 3.5-V to 24-V Input Operating Voltage
– Supports USB2.0, USB 3.0, USB 3.1 (Type C),
and USB_PD Input Current Settings
– Seamless Transition Between Buck and Boost
Operation
– Input current and Voltage Regulation (IDPM
and VDPM) Against Source Overload
Power/Current Monitor for CPU Throttling
– Comprehensive PROCHOT Profile, IMVP8
Compliant
– Input and Battery Current Monitor
– System Power Monitor, IMVP8 Compliant
Narrow-VDC (NVDC) Power Path Management
– Instant-On With No Battery or Deeply
Discharged Battery
– Battery Supplements System When Adapter is
Fully-Loaded
– Ideal Diode Operation in Supplement Mode
800-kHz or 1.2-MHz Programmable Switching
Frequency for 1-µH to 3.3-µH Inductor
Host Control Interface for Flexible System
Configuration
– SMBus Port for Optimal System Performance
and Status Reporting
– Hardware Pin to Set Input Current Limit
Without EC Control
Integrated ADC to Monitor Voltage, Current and
Power
High Accuracy Regulation and Monitor
– ±0.5% Charge Voltage Regulation
– ±2% Input/Charge Current Regulation
– ±2% Input/Charge Current Monitor
– ±5% Power Monitor
Safety
– Thermal Shutdown
– Input, System, Battery Overvoltage Protection
– MOSFET Inductor Overcurrent Protection
Low Battery Quiescent Current
•
•
Input Current Optimizer (ICO) to Extract Max Input
Power
Charge any Battery Chemistry: Li+, LiFePO4,
NiCd, NiMH, Lead Acid
Package: 32-Pin 4 × 4 WQFN
2 Applications
•
•
•
Ultra-Books, Notebooks, Detachable, and Tablet
PCs and Power Bank
Industrial and Medical Equipment
Portable Equipment With Rechargeable Batteries
3 Description
The bq25708 is a synchronous NVDC battery buckboost charge controller, offering low component
count, high efficiency solution for space-constraint,
multi-chemistry battery charging applications.
The NVDC-1 configuration allows the system to be
regulated at battery voltage, but not drop below
system minimum voltage. The system keeps
operating even when the battery is completely
discharged or removed. When load power exceeds
input source rating, the battery goes into supplement
mode and prevents the system from crashing.
The bq25708 charges battery from a wide range of
input sources including USB adapter, high voltage
USB PD sources and traditional adapters.
Device Information
PART NUMBER
PACKAGE
bq25708
(1)
BODY SIZE (NOM)
WQFN (32)
4.00 mm × 4.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Application Diagram
VSYS
Adapter
3.5V ± 24V
BATT
(1S-4S)
Q1
Q2
Q3
Q4
SW1BTST1BTST2SW2
HIDRV1
HIDRV2
LODRV1
LODRV2 SYS
VBUS
ACN
/BATDRV
bq25708
ACP
SRP
SRN
IADPT, IBAT,
PSYS, PROCHOT
•
1
•
SMBus
1 Features
Host
Copyright © 2017, Texas Instruments Incorporated
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Description (Continued) ........................................
Pin Configuration and Functions .........................
Specifications.........................................................
7.1
7.2
7.3
7.4
7.5
7.6
7.7
8
8.4 Device Functional Modes........................................ 26
8.5 Programming .......................................................... 27
8.6 Register Map........................................................... 29
1
1
1
2
3
4
7
9
Application and Implementation ........................ 60
9.1 Application Information .......................................... 60
9.2 Typical Application ................................................. 60
10 Power Supply Recommendations ..................... 66
11 Layout................................................................... 67
Absolute Maximum Ratings ...................................... 7
ESD Ratings ............................................................ 7
Recommended Operating Conditions....................... 7
Thermal Information .................................................. 8
Electrical Characteristics........................................... 8
Timing Requirements .............................................. 16
Typical Characteristics ........................................... 17
11.1 Layout Guidelines ................................................. 67
11.2 Layout Example .................................................... 68
12 Device and Documentation Support ................. 69
12.1
12.2
12.3
12.4
12.5
12.6
Detailed Description ............................................ 19
8.1 Overview ................................................................ 19
8.2 Functional Block Diagram ...................................... 20
8.3 Feature Description................................................. 21
Device Support ....................................................
Documentation Support .......................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
69
69
69
69
69
69
13 Mechanical, Packaging, and Orderable
Information ........................................................... 69
4 Revision History
2
DATE
REVISION
NOTES
November 2017
*
Initial release.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
5 Description (Continued)
During power up, the charger sets converter to buck, boost or buck-boost configuration based on input source
and battery conditions. The charger automatically transits among buck, boost and buck-boost configuration
without host control.
The bq25708 monitors adapter current, battery current and system power. The flexibly programmed PROCHOT
output goes directly to CPU for throttle back when needed.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
3
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
6 Pin Configuration and Functions
SW1
HIDRV1
BTST1
LODRV1
REGN
PGND
LODRV2
BTST2
32
31
30
29
28
27
26
25
RSN Package
32-Pin WQFN
Top View
NC
5
20
SRP
ILIM_HIZ
6
19
SRN
VDDA
7
18
CELL_BATPRESZ
IADPT
8
17
COMP2
16
BATDRV
COMP1
21
15
4
CMPOUT
CHRG_OK
14
VSYS
CMPIN
22
13
3
SCL
ACP
12
SW2
SDA
23
11
2
PROCHOT
ACN
10
HIDRV2
PSYS
24
9
1
IBAT
VBUS
Pin Functions
PIN
NAME
NUMBER
I/O
DESCRIPTION
ACN
2
PWR
Input current sense resistor negative input. The leakage on ACP and ACN are matched. The
series resistors on the ACP and ACN pins are placed between sense resistor and filter cap.
Refer to Application and Implementation for ACP/ACN filter design.
ACP
3
PWR
Input current sense resistor positive input. The leakage on ACP and ACN are matched. The
series resistors on the ACP and ACN pins are placed between sense resistor and filter cap.
Refer to Application and Implementation for ACP/ACN filter design.
BATDRV
21
O
P-channel battery FET (BATFET) gate driver output. It is shorted to VSYS to turn off the
BATFET. It goes 10 V below VSYS to fully turn on BATFET. BATFET is in linear mode to
regulate VSYS at minimum system voltage when battery is depleted. BATFET is fully on
during fast charge and supplement mode.
BTST1
30
PWR
Buck mode high side power MOSFET driver power supply. Connect a 0.047-µF capacitor
between SW1 and BTST1. The bootstrap diode between REGN and BTST1 is integrated.
BTST2
25
PWR
Boost mode high side power MOSFET driver power supply. Connect a 0.047-μF capacitor
between SW2 and BTST2. The bootstrap diode between REGN and BTST2 is integrated.
CELL_BATPRESZ
18
I
Battery cell selection pin for 1–4 cell battery setting. CELL_BATPRESZ pin is biased from
VDDA. CELL_BATPRESZ pin also sets SYSOVP threshold to 5 V for 1-cell, 12 V for 2-cell ,
and 19.5 for 3-cell/4-cell. CELL_BATPRESZ pin is pulled below VCELL_BATPRESZ_FALL to
indicate battery removal. The device exits LEARN mode, and disables charge. REG0x15()
goes back to default.
CHRG_OK
4
O
Open drain active high indicator to inform the system good power source is connected to the
charger input. Connect to the pullup rail via 10-kΩ resistor. When VBUS rises above 3.5V or
falls below 24.5V, CHRG_OK is HIGH after 50ms deglitch time. When VBUS is falls below
3.2V or rises above 26V, CHRG_OK is LOW.
4
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Pin Functions (continued)
PIN
NAME
NUMBER
I/O
DESCRIPTION
CMPIN
14
I
Input of independent comparator. The independent comparator compares the voltage sensed
on CMPIN pin to internal reference, and its output is on CMPOUT pin. Internal reference,
output polarity and deglitch time is selectable by SMBus. With polarity HIGH
(REG0x30[6]=1), place a resistor between CMPIN and CMPOUT to program hysteresis. With
polarity LOW (REG0x30[6]=0), the internal hysteresis is 100 mV. If the independent
comparator is not in use, tie CMPIN to ground.
CMPOUT
15
O
Open-drain output of independent comparator. Place pullup resistor from CMPOUT to pullup
supply rail. Internal reference, output polarity and deglitch time are selectable by SMBus.
COMP2
17
I
Buck boost converter compensation pin 2. Refer to bq25700 EVM schematic for COMP2 pin
RC network.
COMP1
16
I
Buck boost converter compensation pin 1. Refer to bq25700 EVM schematic for COMP1 pin
RC network.
NC
5
HIDRV1
31
O
Buck mode high side power MOSFET (Q1) driver. Connect to high side n-channel MOSFET
gate.
HIDRV2
24
O
Boost mode high side power MOSFET(Q4) driver. Connect to high side n-channel MOSFET
gate.
O
Buffered adapter current output. V(IADPT) = 20 or 40 × (V(ACP) – V(ACN)). With ratio selectable
in REG0x12[4]. Place a resistor from the IADPT pin to ground corresponding to inductor in
use. For 2.2 µH, the resistor is 100 kΩ. Place 100-pF or less ceramic decoupling capacitor
from IADPT pin to ground. IADPT output voltage is clamped below 3.3 V.
O
Buffered battery current selected by SMBus. V(IBAT) = 8 or 16 × (V(SRP) – V(SRN)) for charge
current, or V(IBAT) = 8 or 16 × (V(SRN) – V(SRP)) for discharge current, with ratio selectable in
REG0x12[3]. Place 100-pF or less ceramic decoupling capacitor from IBAT pin to ground.
This pin can be floating if not in use. Its output voltage is clamped below 3.3 V.
IADPT
IBAT
8
9
Not Connected
ILIM_HIZ
6
I
Input current limit input. Program ILIM_HIZ voltage by connecting a resistor divider from
supply rail to ILIM_HIZ pin to ground. The pin voltage is calculated as: V(ILIM_HIZ) = 1 V + 40
× IDPM × RAC, in which IDPM is the target input current. The input current limit used by the
charger is the lower setting of ILIM_HIZ pin and REG0x3F(). When the pin voltage is below
0.4 V, the device enters Hi-Z mode with low quiescent current. When the pin voltage is
above 0.8 V, the device is out of Hi-Z mode.
LODRV1
29
O
Buck mode low side power MOSFET (Q2) driver. Connect to low side n-channel MOSFET
gate.
LODRV2
26
O
Boost mode low side power MOSFET (Q3) driver. Connect to low side n-channel MOSFET
gate.
PGND
27
GND
PROCHOT
11
O
Active low open drain output of processor hot indicator. It monitors adapter input current,
battery discharge current, and system voltage. After any event in the PROCHOT profile is
triggered, a pulse is asserted. The minimum pulse width is adjustable in REG0x33[5:2].
Current mode system power monitor. The output current is proportional to the total power
from the adapter and battery. The gain is selectable through SMBus. Place a resistor from
PSYS to ground to generate output voltage. This pin can be floating if not in use. Its output
voltage is clamped below 3.3 V. Place a capacitor in parallel with the resistor for filtering.
PSYS
10
O
REGN
28
PWR
SCL
13
I
SDA
12
I/O
SRN
19
PWR
Device power ground.
6-V linear regulator output supplied from VBUS or VSYS. The LDO is active when VBUS
above UVLO. Connect a 2.2- or 3.3-μF ceramic capacitor from REGN to power ground.
REGN pin output is for power stage gate drive.
SMBus clock input. Connect to clock line from the host controller or smart battery. Connect a
10-kΩ pullup resistor according to SMBus specifications.
SMBus open-drain data I/O. Connect to data line from the host controller or smart battery.
Connect a 10-kΩ pullup resistor according to SMBus specifications.
Charge current sense resistor negative input. SRN pin is for battery voltage sensing as well.
Connect SRN pin with optional 0.1-μF ceramic capacitor to GND for common-mode filtering.
Connect a 0.1-μF ceramic capacitor from SRP to SRN to provide differential mode filtering.
The leakage current on SRP and SRN are matched. For reverse battery plug-in protection,
10-Ω series resistors are placed on SRP and SRN.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
5
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Pin Functions (continued)
PIN
NAME
NUMBER
I/O
DESCRIPTION
SRP
20
PWR
Charge current sense resistor positive input. Connect 0.1-μF ceramic capacitor from SRP to
SRN to provide differential mode filtering. The leakage current on SRP and SRN are
matched. For reverse battery plug-in protection, 10-Ω series resistors are placed on SRP and
SRN. Connect SRP pin with optional 0.1-uF ceramic capacitor to GND for common-mode
filtering.
SW1
32
PWR
Buck mode high side power MOSFET driver source. Connect to the source of the high side
n-channel MOSFET.
SW2
23
PWR
Boost mode high side power MOSFET driver source. Connect to the source of the high side
n-channel MOSFET.
VBUS
1
PWR
Charger input voltage. An input low pass filter of 1 Ω and 0.47 µF (minimum) is
recommended.
VDDA
7
PWR
Internal reference bias pin. Connect a 10-Ω resistor from REGN to VDDA and a 1-μF
ceramic capacitor from VDDA to power ground.
VSYS
22
PWR
Charger system voltage sensing. The system voltage regulation limit is programmed in
REG0x15() and REG0x3E().
Thermal pad
–
–
6
Exposed pad beneath the IC. Analog ground and power ground star-connected near the IC's
ground. Always solder thermal pad to the board, and have vias on the thermal pad plane
connecting to power ground planes. It also serves as a thermal pad to dissipate the heat.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2)
MIN
MAX
SRN, SRP, ACN, ACP, VBUS, VSYS, BATDRV
–0.3
30
SW1, SW2
–2.0
30
BTST1, BTST2, HIDRV1, HIDRV2
–0.3
36
LODRV1, LODRV2 (25 ns)
–4.0
7
HIDRV1, HIDRV2 (25 ns)
–4.0
36
SW1, SW2 (25 ns)
–4.0
30
SDA, SCL, REGN, CHRG_OK, CELL_BATPRESZ,
ILIM_HIZ, LODRV1, LODRV2, VDDA, COMP1, COMP2,
CMPIN, CMPOUT
–0.3
7
PROCHOT
–0.3
5.5
IADPT, IBAT, PSYS
–0.3
3.6
BTST1-SW1, BTST2-SW2, HIDRV1-SW1, HIDRV2-SW2
–0.3
7
SRP-SRN, ACP-ACN
–0.5
0.5
Junction temperature range, TJ
–40
155
°C
Storage temperature, Tstg
–40
155
°C
Voltage
Differential voltage
(1)
(2)
UNIT
V
V
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to GND if not specified. Currents are positive into, negative out of the specified terminal. Consult Packaging
Section of the data book for thermal limitations and considerations of packages.
7.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±500
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
ACN, ACP, VBUS
0
24
SRN, SRP, VSYS, BATDRV
0
19.2
SW1, SW2
UNIT
–2
24
BTST1, BTST2, HIDRV1, HIDRV2
0
30
SDA, SCL, REGN, CHRG_OK, CELL_BATPRESZ, ILIM_HIZ, LODRV1,
LODRV2, VDDA, COMP1, COMP2, CMPIN, CMPOUT
0
6.5
PROCHOT
0
5.3
IADPT, IBAT, PSYS
0
3.3
BTST1-SW1, BTST2-SW2, HIDRV1-SW1, HIDRV2-SW2
0
6.5
–0.35
0.35
Junction temperature, TJ
–40
125
°C
Operating free-air temperature, TA
–40
85
°C
Voltage
Differential
voltage
SRP-SRN, ACP-ACN
V
V
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
7
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
7.4 Thermal Information
bq25708
THERMAL METRIC (1)
RSN (WQFN)
UNIT
32 PINS
RθJA
Junction-to-ambient thermal resistance
37.2
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
26.1
°C/W
RθJB
Junction-to-board thermal resistance
7.8
°C/W
ψJT
Junction-to-top characterization parameter
0.3
°C/W
ψJB
Junction-to-board characterization parameter
7.8
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
2.3
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
7.5 Electrical Characteristics
over operating free-air temperature range (unless otherwise noted)
PARAMETER
VINPUT_OP
TEST CONDITIONS
Input voltage operating range
MIN
TYP
MAX
UNIT
3.5
26
V
1.024
19.2
V
REGULATION ACCURACY
MAX SYSTEM VOLTAGE REGULATION
VSYSMAX_RNG
System voltage regulation,
measured on VSYS
REG0x15() = 0x41A0H
(16.800 V)
VSYSMAX_ACC
System voltage regulation
accuracy (charge disable)
REG0x15() = 0x3130H
(12.592 V)
VSRN + 160 mV
–2%
V
2%
VSRN + 160 mV
–2%
V
2%
VSRN + 160 mV
V
REG0x15() = 0x20D0H
(8.400 V)
–3%
REG0x15() = 0x1060H
(4.192 V)
–3%
3%
1.024
19.2
3%
VSRN + 160 mV
V
MINIMUM SYSTEM VOLTAGE REGULATION
VSYSMIN_RNG
System voltage regulation,
measured on VSYS
REG0x3E() = 0x3000H
VSYSMIN_REG_ACC
Minimum system voltage
regulation accuracy (charge
enable, VBAT below
REG0x3E() setting)
REG0x3E() = 0x2400H
REG0x3E() = 0x1800H
REG0x3E() = 0x0E00H
12.288
–2%
V
V
2%
9.216
–2%
V
2%
6.144
–3%
V
3%
3.584
–3%
V
4%
CHARGE VOLTAGE REGULATION
VBAT_RNG
Battery voltage regulation
1.024
REG0x15() = 0x41A0H
VBAT_REG_ACC
Battery voltage regulation
accuracy (charge enable)
(0°C to 85°C)
REG0x15() = 0x3130H
REG0x15() = 0x20D0H
REG0x15() = 0x1060H
8
Submit Documentation Feedback
19.2
16.8
–0.5%
V
0.5%
12.592
–0.5%
V
0.5%
8.4
–0.6%
V
0.6%
4.192
–1.1%
V
V
1.2%
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Electrical Characteristics (continued)
over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
81.28
mV
CHARGE CURRENT REGULATION IN FAST CHARGE
VIREG_CHG_RNG
Charge current regulation
differential voltage range
VIREG_CHG = VSRP –
VSRN
REG0x14() = 0x1000H
ICHRG_REG_ACC
Charge current regulation
REG0x14() = 0x0800H
accuracy 10-mΩ current
sensing resistor, VBAT above
REG0x14() = 0x0400H
0x3E() setting (0°C to 85°C)
REG0x14() = 0x0200H
0
4096
–3%
mA
2%
2048
–4%
mA
3%
1024
–5%
mA
5%
512
–12%
mA
12%
CHARGE CURRENT REGULATION IN LDO MODE
ICLAMP
Pre-charge current clamp
CELL 2s-4s
384
mA
CELL 1 s, VSRN < 3 V
384
mA
CELL 1 s, 3 V < VSRN <
VSYS_MIN
2
REG0x14() = 0x0180H
384
2S-4S
–15%
1S
–25%
REG0x14() = 0x0100H
IPRECHRG_REG_ACC
Pre-charge current regulation
accuracy with 10-mΩ
SRP/SRN series resistor,
VBAT below REG0x3E()
setting (0°C to 85°C)
–20%
1S
–35%
REG0x14() = 0x00C0H
15%
25%
mA
20%
35%
192
2S-4S
–25%
1S
–50%
REG0x14() = 0x0080H
ILEAK_SRP_SRN
mA
256
2S-4S
2S-4S
A
mA
25%
50%
128
mA
–30%
30%
–12
–10
µA
0.5
64
mV
REG0x3F() = 0x4FFFH
3820
4000
mA
REG0x3F() = 0x3BFFH
2830
3000
mA
REG0x3F() = 0x1DFFH
1350
1500
mA
REG0x3F() = 0x09FFH
340
500
mA
–16
10
µA
1
4
V
SRP, SRN leakage current
mismatch (0°C to 85°C)
INPUT CURRENT REGULATION
VIREG_DPM_RNG
Input current regulation
differential voltage range
IDPM_REG_ACC
Input current regulation
accuracy with 10-mΩ
ACP/ACN series resistor
(–40°C to 105°C)
VIREG_DPM = VACP – VACN
ILEAK_ACP_ACN
ACP, ACN leakage current
mismatch
VIREG_DPM_RNG_ILIM
Voltage Range for input
current regulation
IDPM_REG_ACC_ILIM
VILIM_HIZ = 2.6 V
Input Current Regulation
Accuracy on ILIM_HIZ pin
VILIM_HIZ = 2.2 V
VILIM_HIZ = 1 V + 40 × IDPM ×
VILIM_HIZ = 1.6 V
RAC, with 10-mΩ ACP/ACN
series resistor
VILIM_HIZ = 1.2 V
ILEAK_ILIM
ILIM_HIZ pin leakage
3800
4000
4200
mA
2800
3000
3200
mA
1300
1500
1700
mA
300
500
700
mA
1
µA
–1
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
9
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Electrical Characteristics (continued)
over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
INPUT VOLTAGE REGULATION
VIREG_DPM_RNG
Input voltage regulation range Voltage on VBUS
3.2
REG0x3D()=0x3C80H
19.52
18688
–2%
VDPM_REG_ACC
Input voltage regulation
accuracy
REG0x3D()=0x1E00H
2%
10880
–2.5%
REG0x3D()=0x0500H
V
mV
mV
2.5%
4480
–3%
mV
5%
REFERENCE AND BUFFER
REGN REGULATOR
VREGN_REG
REGN regulator voltage (0
mA–60 mA)
VVBUS = 10 V
5.7
6
6.3
V
VDROPOUT
REGN voltage in drop out
mode
VVBUS = 5 V, ILOAD = 20 mA
3.8
4.3
4.6
V
IREGN_LIM_Charging
REGN current limit when
converter is enabled
VVBUS = 10 V, force VREGN =
4V
50
65
CREGN
REGN output capacitor
required for stability
ILOAD = 100 µA to 50 mA
2.2
µF
CVDDA
REGN output capacitor
required for stability
ILOAD = 100 µA to 50 mA
1
µF
mA
QUIESCENT CURRENT
VBAT = 18 V, REG0x12[15]
= 1, in low power mode
22
45
µA
VBAT = 18 V, REG0x12[15]
= 1, in low power mode,
REG0x30[14:13] = 01,
REGN off
105
175
µA
VBAT=18 V, REG0x12[15] =
1, in low power mode,
REG0x30[14:13]= 10,
REGN off
60
90
µA
VBAT = 18 V, REG0x12[15]
= 0, REG0x30[12] = 0,
REGN on, EN_PSYS
860
1150
VBAT = 18 V, REG0x12[15]
= 0, REG0x30[12] = 1,
REGN on
960
IAC_SW_LIGHT_buck
Input current during PFM in
buck mode, no load, IVBUS +
IACP + IACN + IVSYS + ISRP +
ISRN + ISW1 + IBTST + ISW2 +
IBTST2
VIN = 20 V, VBAT = 12.6 V,
3 s, REG0x12[10] = 0;
MOSFET Qg = 4 nC
2.2
mA
IAC_SW_LIGHT_boost
Input current during PFM in
boost mode, no load, IVBUS +
IACP + IACN + IVSYS + ISRP +
ISRN + ISW1 + IBTST2 + ISW2 +
IBTST2
VIN = 5 V, VBAT = 8.4 V, 2
s, REG0x12[10] = 0;
MOSFET Qg = 4 nC
2.7
mA
IAC_SW_LIGHT_buckboost
Input current during PFM in
buck boost mode, no load,
IVBUS + IACP + IACN + IVSYS +
ISRP + ISRN + ISW1 + IBTST1 +
ISW2 + IBTST2
VIN = 12 V, VBAT = 12 V,
REG0x12[10] = 0; MOSFET
Qg = 4 nC
2.4
mA
VACP/N_OP
Input common mode range
Voltage on ACP/ACN
VIADPT_CLAMP
IADPT output clamp voltage
IIADPT
IADPT output current
IBAT_BATFET_ON
10
System powered by battery.
BATFET on. ISRN + ISRP +
ISW2+ IBTST2 + ISW1 + IBTST1+
ACP + IACN + IVBUS + IVSYS
µA
3.8
3.1
1250
26
3.2
3.3
1
Submit Documentation Feedback
V
V
mA
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Electrical Characteristics (continued)
over operating free-air temperature range (unless otherwise noted)
PARAMETER
AIADPT
TEST CONDITIONS
Input current sensing gain
MAX
UNIT
20
V/V
V(IADPT) / V(ACP-ACN),
REG0x12[4] = 1
40
V/V
V(ACP-ACN) = 40.96 mV
–2%
2%
V(ACP-ACN) = 20.48 mV
–3%
3%
V(ACP-ACN) =10.24 mV
–6%
6%
V(ACP-ACN) = 5.12 mV
–10%
10%
Input current monitor
accuracy
CIADPT_MAX
Maximum output load
capacitance
VSRP/N_OP
Battery common mode range
VIBAT_CLAMP
IBAT output clamp voltage
IIBAT
IBAT output current
AIBAT
V(IBAT) / V(SRN-SRP),
Charge and discharge current REG0x12[3] = 0,
sensing gain on IBAT pin
V(IBAT) / V(SRN-SRP),
REG0x12[3] = 1,
Voltage on SRP/SRN
2.5
3.1
3.2
100
pF
18
V
3.3
1
V
mA
8
V/V
16
V/V
V(SRN-SRP) = 40.96 mV
–2%
2%
Charge and discharge current V(SRN-SRP) = 20.48 mV
monitor accuracy on IBAT pin V(SRN-SRP) =10.24 mV
–3%
4%
V(SRN-SRP) = 5.12 mV
CIBAT_MAX
TYP
V(IADPT) / V(ACP-ACN),
REG0x12[4] = 0
VIADPT_ACC
IIBAT_CHG_ACC
MIN
–6%
6%
–12%
12%
Maximum output load
capacitance
100
pF
SYSTEM POWER SENSE AMPLIFIER
VPSYS
PSYS output voltage range
0
3.3
V
IPSYS
PSYS output current
0
160
µA
APSYS
PSYS system gain
VPSYS_ACC
PSYS gain accuracy
(REG0x3B[9] = 1), TA = 25°C
VPSYS_CLAMP
V(PSYS) / (P(IN)+ P(BAT)),
REG0x30[9] = 1
1
µA/W
Adapter only with system
power = 19.5 V / 45 W
–5%
5%
Battery only with system
power 11 V / 44 W (25°C)
–5%
5%
3
3.3
V
PSYS clamp voltage
COMPARATOR
VBUS UNDER VOLTAGE LOCKOUT COMPARATOR
VVBUS_UVLOZ
VBUS undervoltage rising
threshold
VBUS rising
2.34
2.55
2.77
V
VVBUS_UVLO
VBUS undervoltage falling
threshold
VBUS falling
2.2
2.4
2.6
V
VVBUS_UVLO_HYST
VBUS undervoltage
hysteresis
VVBUS_CONVEN
VBUS converter enable rising
threshold
VBUS rising
3.2
3.5
3.9
V
VVBUS_CONVENZ
VBUS converter enable falling
VBUS falling
threshold
2.9
3.2
3.5
V
VVBUS_CONVEN_HYST
VBUS converter enable
hysteresis
150
mV
400
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
mV
11
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Electrical Characteristics (continued)
over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
BATTERY UNDER VOLTAGE LOCKOUT COMPARATOR
VVBAT_UVLOZ
VBAT undervoltage rising
threshold
VSRN rising
2.35
2.55
2.75
V
VVBAT_UVLO
VBAT undervoltage falling
threshold
VSRN falling
2.2
2.4
2.6
V
VVBAT_UVLO_HYST
VBAT undervoltage
hysteresis
150
mV
2.80
V
BATTERY LOWV COMPARATOR (Pre-charge to Fast Charge Thresold for 1S)
VBATLV_FALL
BATLOWV falling threshold
VBATLV_RISE
BATLOWV rising threshold
1s
3.00
V
VBATLV_RHYST
BATLOWV hysteresis
200
mV
INPUT OVER-VOLTAGE COMPARATOR (ACOVP)
VACOV_RISE
VBUS overvoltage rising
threshold
VBUS rising
25
26
27
V
VACOV_FALL
VBUS overvoltage falling
threshold
VBUS falling
24
24.5
25
V
VACOV_HYST
VBUS overvoltage hysteresis
1.5
V
tACOV_RISE_DEG
VBUS overvoltage rising
deglitch
VBUS rising to stop
converter
100
µs
tACOV_FALL_DEG
VBUS overvoltage falling
deglitch
VBUS falling to start
converter
1
ms
INPUT OVER CURRENT COMPARATOR (ACOC)
VACOC
ACP to ACN rising threshold,
w.r.t. ILIM2 in
REG0x33[15:11]
Voltage across input sense
resistor rising, Reg0x31[2] =
1
VACOC_FLOOR
Measure between ACP and
ACN
VACOC_CEILING
195%
210%
225%
Set IDPM to minimum
44
50
56
mV
Measure between ACP and
ACN
Set IDPM to maximum
172
180
188
mV
tACOC_DEG_RISE
Rising deglitch time
Deglitch time to trigger
ACOC
250
µs
tACOC_RELAX
Relax time
Relax time before converter
starts again
250
ms
SYSTEM OVER-VOLTAGE COMPARATOR (SYSOVP)
VSYSOVP_RISE
System overvoltage rising
threshold to turn off converter
1s
4.85
5
5.1
V
2s
11.7
12
12.2
V
18
18.5
19
V
3s
VSYSOVP_FALL
System overvoltage falling
threshold
ISYSOVP
Discharge current when
SYSOVP stop switching was
triggered
1s
4.8
V
2s
11.5
V
3s
18
V
on SYS
20
mA
BAT OVER-VOLTAGE COMPARATOR (BATOVP)
Overvoltage rising threshold
as percentage of VBAT_REG in
REG0x15()
1 s, 4.2 V
102.5%
104%
105.7%
VBATOVP_RISE
2s-4s
102.5%
104%
105%
Overvoltage falling threshold
as percentage of VBAT_REG
in REG0x15()
1s
100%
102%
104%
VBATOVP_FALL
2s-4s
100%
102%
103%
Overvoltage hysteresis as
percentage of VBAT_REG in
REG0x15()
1s
2%
VBATOVP_HYST
2s-4s
2%
12
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Electrical Characteristics (continued)
over operating free-air temperature range (unless otherwise noted)
PARAMETER
IBATOVP
Discharge current during
BATOVP
tBATOVP_RISE
Overvoltage rising deglitch to
turn off BATDRV to disable
charge
TEST CONDITIONS
MIN
on SRP and SRN
TYP
MAX
UNIT
20
mA
20
ms
CONVERTER OVER-CURRENT COMPARATOR (Q2)
VOCP_limit_Q2
Converter Over-Current Limit
VOCP_limit_SYSSH
ORT_Q2
System Short or SRN<2.5 V
Reg0x31[5]=1
150
Reg0x31[5]=0
210
Reg0x31[5]=1
45
Reg0x31[5]=0
60
mV
mV
CONVERTER OVER-CURRENT COMPARATOR (ACX)
VOCP_limit_ACX
Converter Over-Current Limit
VOCP_limit_SYSSH
ORT_ ACX
System Short or SRN<2.5 V
Reg0x31[4]=1
150
Reg0x31[4]=0
280
Reg0x31[4]=1
90
Reg0x31[4]=0
150
mV
mV
THERMAL SHUTDOWN COMPARATOR
TSHUT_RISE
Thermal shutdown rising
temperature
Temperature increasing
155
°C
TSHUTF_FALL
Thermal shutdown falling
temperature
Temperature reducing
135
°C
TSHUT_HYS
Thermal shutdown hysteresis
20
°C
tSHUT_RDEG
Thermal shutdown rising
deglitch
100
µs
tSHUT_FHYS
Thermal shutdown falling
deglitch
12
ms
VSYS PROCHOT COMPARATOR
Reg0x36[7:6] = 00, 1 s
2.85
V
Reg0x36[7:6] = 00, 2–4 s
5.75
V
Reg0x36[7:6] = 01, 1 s
VSYS_PROCHOT
VSYS threshold falling
threshold
Reg0x36[7:6] = 01, 2–4 s
2.95
3.1
3.25
V
5.8
5.95
6.1
V
Reg0x36[7:6] = 10, 1 s
Reg0x36[7:6] = 10, 2–4 s
tSYS_PRO_RISE_DEG
3.3
V
6.25
V
Reg0x36[7:6] = 11, 1 s
3.5
V
Reg0x36[7:6] = 11, 2–4 s
6.5
V
8
µs
VSYS rising deglitch for
throttling
ICRIT PROCHOT COMPARATOR
VICRIT_PRO
Input current rising threshold
for throttling as percentage
above ILIM2
(REG0x33[15:11])
Reg0x36[15:11] = 00000
105%
110%
116%
Reg0x36[15:11] = 01001
142%
150%
155%
Reg0x36[15:11] = 11110
410%
430%
455%
105%
110%
116%
INOM PROCHOT COMPARATOR
VINOM_PRO
INOM rising threshold as
percentage of IIN
(REG0x3F())
IDCHG PROCHOT COMPARATOR
VIDCHG_PRO
IDCHG threshold for throttling
Reg0x38 [15:10]=001100
for IDSCHG of 6 A
6144
95%
mA
102%
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
13
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Electrical Characteristics (continued)
over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Reg0x30[7] = 1, CMPIN
falling
1.17
1.2
1.23
V
Reg0x30[7] = 0, CMPIN
falling
2.27
2.3
2.33
V
INDEPENDENT COMPARATOR
VINDEP_CMP
VINDEP_CMP_HYS
Independent comparator
threshold
Independent comparator
hysteresis
Reg0x06[6] = 0, CMPIN
falling
100
mV
POWER MOSFET DRIVER
PWM OSCILLATOR AND RAMP
FSW
PWM switching frequency
Reg0x00[9] = 0
1020
1200
1380
kHz
Reg0x00[9] = 1
680
800
920
kHz
8.5
10
11.5
V
BATFET GATE DRIVER (BATDRV)
VBATDRV_ON
Gate drive voltage on
BATFET
VBATDRV_DIODE
Drain-source voltage on
BATFET during ideal diode
operation
RBATDRV_ON
Measured by sourcing 10-µA
current to BATDRV
RBATDRV_OFF
Measured by sinking 10-µA
current from BATDRV
30
3
mV
4
6
kΏ
1.2
2.1
kΏ
PWM HIGH SIDE DRIVER (HIDRV Q1)
RDS_HI_ON_Q1
High side driver (HSD) turnon
VBTST1 – VSW1 = 5 V
resistance
RDS_HI_OFF_Q1
High side driver turnoff
resistance
VBTST1 – VSW1 = 5 V
VBTST1_REFRESH
Bootstrap refresh comparator
falling threshold voltage
VBTST1 – VSW1 when low
side refresh pulse is
requested
6
3.2
Ω
1.3
2.2
Ω
3.7
4.6
V
PWM HIGH SIDE DRIVER (HIDRV Q4)
RDS_HI_ON_Q4
High side driver (HSD) turnon
VBTST2 – VSW2 = 5 V
resistance
RDS_HI_OFF_Q4
High side driver turnoff
resistance
VBTST2 – VSW2 = 5 V
VBTST2_REFRESH
Bootstrap refresh comparator
falling threshold voltage
VBTST2 – VSW2 when low
side refresh pulse is
requested
6
3.3
Ω
1.5
2.4
Ω
3.7
4.6
V
PWM LOW SIDE DRIVER (LODRV Q2)
RDS_LO_ON_Q2
Low side driver (LSD) turnon
resistance
VBTST1 – VSW1 = 5.5 V
6
RDS_LO_OFF_Q2
Low side driver turnoff
resistance
VBTST1 – VSW1 = 5.5 V
1.7
Ω
2.6
Ω
PWM LOW SIDE DRIVER (LODRV Q3)
RDS_LO_ON_Q3
Low side driver (LSD) turnon
resistance
VBTST2 – VSW2 = 5.5 V
7.6
RDS_LO_OFF_Q3
Low side driver turnoff
resistance
VBTST2 – VSW2 = 5.5 V
2.9
Ω
4.6
Ω
INTERNAL SOFT START During Charge Enable
SSSTEP_DAC
Soft Start Step Size
64
mA
SSSTEP_DAC
Soft Start Step Time
8
µs
14
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Electrical Characteristics (continued)
over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
INTEGRATED BTST DIODE (D1)
VF_D1
Forward bias voltage
IF = 20 mA at 25°C
VR_D1
Reverse breakdown voltage
IR = 2 µA at 25°C
0.8
V
20
V
INTEGRATED BTST DIODE (D2)
VF_D2
Forward bias voltage
IF = 20 mA at 25°C
VR_D2
Reverse breakdown voltage
IR = 2 µA at 25°C
0.8
20
V
V
0.8
V
PWM DRIVERS TIMING
INTERFACE
LOGIC INPUT (SDA, SCL)
VIN_
LO
Input low threshold
SMBus
VIN_
HI
Input high threshold
SMBus (bq25708)
2.1
V
LOGIC OUTPUT OPEN DRAIN (SDA, CHRG_OK, CMPOUT)
VOUT_
LO
Output saturation voltage
5-mA drain current
VOUT_
LEAK
Leakage current
V=7V
0.4
–1
1
V
mA
LOGIC OUTPUT OPEN DRAIN SDA
VOUT_
VOUT_
LO_SDA
Output Saturation Voltage
5 mA drain current
LEAK_SDA
Leakage Current
V = 7V
0.4
–1
1
V
mA
LOGIC OUTPUT OPEN DRAIN CHRG_OK
VOUT_
LO_CHRG_OK
VOUT_ LEAK _CHRG_OK
Output Saturation Voltage
5 mA drain current
Leakage Current
V = 7V
0.4
–1
1
V
mA
LOGIC OUTPUT OPEN DRAIN CMPOUT
VOUT_
LO_CMPOUT
VOUT_ LEAK _CMPOUT
Output Saturation Voltage
5 mA drain current
Leakage Current
V = 7V
0.4
–1
V
1
mA
300
mV
1
mA
LOGIC OUTPUT OPEN DRAIN (PROCHOT)
VOUT_
LO_PROCHOT
Output saturation voltage
50-Ω pullup to 1.05 V / 5-mA
load
VOUT_
LEAK_PROCHOT
Leakage current
V = 5.5 V
–1
0.8
ANALOG INPUT (ILIM_HIZ)
VHIZ_
LO
Voltage to get out of HIZ
mode
ILIM_HIZ pin rising
VHIZ_
HIGH
Voltage to enable HIZ mode
ILIM_HIZ pin falling
V
0.4
V
ANALOG INPUT (CELL_BATPRESZ)
VCELL_4S
4S
REGN = 6 V, as percentage
of REGN
68.4%
75%
VCELL_3S
3s
REGN = 6 V, as percentage
of REGN
51.7%
55%
65%
VCELL_2S
2S
REGN = 6 V, as percentage
of REGN
35%
40%
49.1%
VCELL_1S
1S
REGN = 6 V, as percentage
of REGN
18.4%
25%
31.6%
VCELL_BATPRESZ_RISE
Battery is present
VCELL_BATPRESZ_FALL
Battery is removed
18%
CELL_BATPRESZ falling
15%
ANALOG INPUT (COMP1, COMP2)
ILEAK_COMP1
COMP1 Leakage
–120
120
nA
ILEAK_COMP2
COMP2 Leakage
–120
120
nA
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
15
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
7.6 Timing Requirements
MIN
TYP MAX
UNIT
SMBus TIMING CHARACTERISTICS
tr
SCLK/SDATA rise time
tf
SCLK/SDATA fall time
1
µs
300
ns
tW(H)
SCLK pulse width high
4
tW(L)
SCLK Pulse Width Low
4.7
50
µs
µs
tSU(STA)
Setup time for START condition
4.7
µs
tH(STA)
START condition hold time after which first clock pulse is generated
4
µs
tSU(DAT)
Data setup time
250
µs
tH(DTA)
Data hold time
300
µs
tSU(STOP)
Setup time for STOP condition
4
µs
t(BUF)
Bus free time between START and STOP condition
4.7
FS(CL)
Clock Frequency
10
100
KHz
35
ms
µs
HOST COMMUNICATION FAILURE
ttimeout
SMBus bus release timeout (1)
25
tBOOT
Deglitch for watchdog reset signal
10
Watchdog timeout period, ChargeOption() bit [14:13] = 01 (2)
35
tWDI
Watchdog timeout period, ChargeOption() bit [14:13] = 10
(2)
Watchdog timeout period, ChargeOption() bit [14:13] = 11 (2) (default)
(1)
(2)
16
ms
44
53
s
70
88
105
s
140
175
210
s
Devices participating in a transfer will timeout when any clock low exceeds the 25ms minimum timeout period. Devices that have
detected a timeout condition must reset the communication no later than the 35 ms maximum timeout period. Both a master and a slave
must adhere to the maximum value specified as it incorporates the cumulative stretch limit for both a master (10 ms) and a slave (25
ms).
User can adjust threshold via SMBus ChargeOption() REG0x12.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
90
90
85
85
80
80
Efficiency (%)
Efficiency (%)
7.7 Typical Characteristics
75
70
VOUT = 6.1 V
VOUT = 8.4 V
VOUT = 9.2 V
VOUT = 12.5 V
65
75
70
VOUT = 6.1 V
VOUT = 8.4 V
VOUT = 9.2 V
VOUT = 12.5 V
65
60
60
0
0.01
0.02
0.03
Output Current (A)
0.04
0.05
0
0.01
0.02
0.03
Output Current (A)
D001
VIN = 5 V
0.04
0.05
D001
VIN = 12 V
Figure 1. Light Load Efficiency
Figure 2. Light Load Efficiency
90
96
94
85
Efficiency (%)
Efficiency (%)
92
80
75
70
88
86
84
VOUT = 6.1 V
VOUT = 8.4 V
VOUT = 9.2 V
VOUT = 12.5 V
65
90
VOUT = 3.7 V
VOUT = 7.4 V
VOUT = 11.1 V
VOUT = 14.8 V
82
60
80
0
0.01
0.02
0.03
Output Current (A)
0.04
0.05
0
1
VIN = 20 V
3
4
Output Current (A)
5
6
D001
VIN = 5 V
Figure 3. Light Load Efficiency
Figure 4. System Efficiency
98
98
96
96
94
94
92
92
Efficiency (%)
Efficiency (%)
2
D001
90
88
86
VOUT = 3.7 V
VOUT = 7.4 V
VOUT = 11.1 V
VOUT = 14.8 V
84
82
90
88
86
VOUT = 3.7 V
VOUT = 7.4 V
VOUT = 11.1 V
VOUT = 14.8 V
84
82
80
80
0
1
2
3
4
Output Current (A)
VIN = 9 V
5
6
0
1
D001
2
3
4
Output Current (A)
5
6
D001
VIN = 12 V
Figure 5. System Efficiency
Figure 6. System Efficiency
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
17
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Typical Characteristics (continued)
98
96
Efficiency (%)
94
92
90
88
86
VOUT = 3.7 V
VOUT = 7.4 V
VOUT = 11.1 V
VOUT = 14.8 V
84
82
80
0
1
2
3
4
Output Current (A)
5
6
D001
VIN = 20 V
Figure 7. System Efficiency
18
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8 Detailed Description
8.1 Overview
The bq25708 is a buck boost NVDC (narrow voltage DC) charge controller for multi-chemistry portable
applications such as notebook, detachable, ultrabook, tablet and other mobile devices with rechargeable
batteries. It provides seamless transition between converter operation modes (buck, boost, or buck boost), fast
transient response, and high light load efficiency.
The bq25708 supports wide range of power sources, including USB PD ports, legacy USB ports, traditional
ACDC adapters, etc. It takes input voltage from 3.5 V to 24 V, and charges battery of 1-4 series.
The bq25708 features Dynamic Power Management (DPM) to limit the input power and avoid AC adapter
overloading. During battery charging, as the system power increases, the charging current will reduce to maintain
total input current below adapter rating. If system power demand temporarily exceeds adapter rating, the
bq25708 supports NVDC architecture to allow battery discharge energy to supplement system power. For details,
refer to System Voltage Regulation section.
In order to be compliant with an Intel IMVP8 compliant system, the bq25708 includes PSYS function to monitor
the total platform power from adapter and battery. Besides PSYS, it provides both an independent input current
buffer (IADPT) and a battery current buffer (IBAT) with highly accurate current sense amplifiers. If the platform
power exceeds the available power from adapter and battery, a PROCHOT signal is asserted to CPU so that the
CPU optimizes its performance to the power available to the system.
The bq25708 controls input current, charge current and charge voltage registers with high resolution, high
accuracy regulation limits. It also sets the PROCHOT timing and threshold profile to meet system requirements.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
19
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.2 Functional Block Diagram
CHRG_OK
4
CHRG_OK_DRV
bq25708 Block Diagram
50ms Rising
Deglitch
** programmable in register
3.9V
EN_REGN
VBUS
1
VREF_CMP**
CMP_DEG**
ACOVP
26V
14
CMPIN
15
CMPOUT
VREF_VDPM
16
VSNS_VDPM
EN_HIZ
ILIM_HIZ
6
ACP
2
ACN
3
IADPT
8
IBAT
9
Decoder
17
VREF_ILIM
COMP1
COMP2
VSYS
VREF_IDPM
LDO Mode
Gate Control
VSNS_IDPM
20X**
VSNS_ICHG
Loop Selector
and
Error Amplifier
20
19
30
BTST1
31
HIDRV1
32
PWM
VREF_ICHG
SRP
BATDRV
VSNS_IDCHG
16X
SRN
21
VSYS-10V
20X**
7
EN_REGN
VSNS_ICHG
REGN
LDO
28
SW1
VDDA
REGN
EN_HIZ
VREF_VBAT
EN_LEARN
VSNS_VBAT
EN_CHRG
EN_LDO
VSYS
22
PWM
Driver
Logic
29
LODRV1
27
PGND
25
BTST2
24
HIDRV2
23
SW2
26
LODRV2
Decoder
18
CELL_BATPRESZ
Processor
Hot
11
PROCHOT
VREF_VSYS
VSNS_VSYS
VSNS_VSYS
ACN
PSYS
10
VSNS_VBAT
VSNS_ICHG
(ACP-ACN)
SRN
VSNS_IDCHG
VSNS_IDPM
(SRN-SRP)
VSNS_VDPM
Over
Current
Over
Voltage
Detect
EN_HIZ
SDA
SCL
12
13
SMBUS
Interface
ChargeOption0()
ChargeOption1()
ChargeOption2()
ChargeCurrent()
ChargeVoltage()
InputCurrent()
InputVoltage()
MinSysVoltage()
EN_LEARN
BATPRESZ
EN_LDO
EN_CHRG
CELL_CONFIG
VREF_VSYS
Loop
Regulation
Reference
VREF_VBAT
VREF_ICHG
VREF_IDPM
VREF_VDPM
VREF_IOTG
VREF_VOTG
IADPT
IBAT
VSYS
CHRG_OK
Copyright © 2017, Texas Instruments Incorporated
20
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.3 Feature Description
8.3.1
Power-Up from Battery Without DC Source
If only battery is present and the voltage is above VVBAT_UVLOZ, the BATFET turns on and connects battery to
system. By default, the charger is in low power mode (REG0x12[15] = 1) with lowest quiescent current. The LDO
stays off. When device moves to performance mode (REG0x12[15] = 0), The host enables IBAT buffer through
SMBus to monitor discharge current. For PSYS, PROCHOT or independent comparator, REGN LDO is enabled
for an accurate reference.
8.3.2 Power-Up From DC Source
When an input source plugs in, the charger checks the input source voltage to turn on LDO and all the bias
circuits. It sets the input current limit before the converter starts.
The power-up sequence from DC source is as follows:
1. 50 ms after VBUS above VVBUS_CONVEN, enable 6V LDO and CHRG_OK goes HIGH
2. Input voltage and current limit setup
3. Battery CELL configuration
4. 150 ms after VBUS above VVBUS_CONVEN, converter powers up.
8.3.2.1 CHRG_OK Indicator
CHRG_OK is an active HIGH open drain indicator. It indicates the charger is in normal operation when the
following conditions are valid:
• VBUS is above VVBUS_CONVEN
• VBUS is below VACOV
• No MOSFET/inductor fault
8.3.2.2
Input Voltage and Current Limit Setup
When CHRG_OK goes LOW, the charger sets default input current limit in REG0x3F() to 3.30A. The actual input
current limit is the lower setting of REG0x3F() and ILIM_HIZ pin.
Charger initiates a VBUS voltage measurement without any load (VBUS at no load condition). The default
VINDPM threshold is [email protected] V.
After input current and voltage limits are set, the charger device is ready to power up. The host can always
update input current and voltage limit based on input source type.
8.3.2.3
Battery Cell Configuration
CELL_BATPRESZ pin is biased with resistors from REGN to CELL_BATPRESZ to GND. After VDDA LDO is
activated, the device detects the battery configuration through CELL_BATPRESZ pin bias voltage. Refer to
Electrical Characteristics for CELL setting thresholds.
Table 1. Battery Cell Configuration
CELL COUNT
PIN VOLTAGE w.r.t. VDDA
BATTERY VOLTAGE (REG0x15)
SYSOVP
4S
75%
16.800V
19.5V
3S
55%
12.592V
19.5V
2S
40%
8.400V
12V
1S
25%
4.192V
5V
8.3.2.4 Device Hi-Z State
The charger enters Hi-Z mode when ILIM_HIZ pin voltage is below 0.4 V or REG0x32[15] is set to 1. During Hi-Z
mode, the input source is present, and the charger is in the low quiescent current mode with REGN LDO
enabled.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
21
bq25708
SLUSCU2 – NOVEMBER 2017
8.3.3
www.ti.com
Converter Operation
The charger employs a synchronous buck-boost converter that allows charging from a standard 5-V or a highvoltage power source. The charger operates in buck, buck-boost and boost mode. The buck-boost can operate
uninterruptedly and continuously across the three operation modes.
Table 2. MOSFET Operation
8.3.3.1
MODE
BUCK
BUCK-BOOST
BOOST
Q1
Switching
Switching
ON
Q2
Switching
Switching
OFF
Q3
OFF
Switching
Switching
Q4
ON
Switching
Switching
Inductor Setting through IADPT Pin
The charger reads the inductor value through the IADPT pin.
Table 3. Inductor Setting on IADPT Pin
INDUCTOR IN USE
RESISTOR ON IADPT PIN
1 µH
93 kΩ
2.2 µH
137 kΩ
3.3 µH
169 kΩ
8.3.3.2 Continuous Conduction Mode (CCM)
With sufficient charge current, the inductor current does not cross 0 A, which is defined as CCM. The controller
starts a new cycle with ramp coming up from 200 mV. As long as error amplifier output voltage is above the ramp
voltage, the high-side MOSFET (HSFET) stays on. When the ramp voltage exceeds error amplifier output
voltage, HSFET turns off and low-side MOSFET (LSFET) turns on. At the end of the cycle, ramp gets reset and
LSFET turns off, ready for the next cycle. There is always break-before-make logic during transition to prevent
cross-conduction and shoot-through. During the dead time when both MOSFETs are off, the body-diode of the
low-side power MOSFET conducts the inductor current.
During CCM, the inductor current always flows and creates a fixed two-pole system. Having the LSFET turn-on
when the HSFET is off, keeps the power dissipation low and allows safe charging at high currents.
8.3.3.3 Pulse Frequency Modulation (PFM)
In order to improve converter light-load efficiency, the bq25708 switches to PFM control at light load condition.
The effective switching frequency will decrease accordingly when system load decreases. The minimum
frequency can be limit to 25kHz (ChargeOption0() bit[10]=1).
8.3.4 Current and Power Monitor
8.3.4.1 High-Accuracy Current Sense Amplifier (IADPT and IBAT)
As an industry standard, a high-accuracy current sense amplifier (CSA) is used to monitor the input current
during forward charging, and the charge/discharge current (IBAT). IADPT voltage is 20× or 40× the differential
voltage across ACP and ACN. IBAT voltage is 8x/16× (during charging), or 8×/16× (during discharging) of the
differential across SRP and SRN. After input voltage or battery voltage is above UVLO, IADPT output becomes
valid. To lower the voltage on current monitoring, a resistor divider from CSA output to GND can be used and
accuracy over temperature can still be achieved.
• V(IADPT) = 20 or 40 × (V(ACP) – V(ACN)) during forward mode.
• V(IBAT) = 8 or 16 × (V(SRP) – V(SRN)) during forward charging mode.
• V(IBAT) = 8 or 16 × (V(SRN) – V(SRP)) during forward supplement mode.
A maximum 100-pF capacitor is recommended to connect on the output for decoupling high-frequency noise. An
additional RC filter is optional, if additional filtering is desired. Note that adding filtering also adds additional
response delay. The CSA output voltage is clamped at 3.3 V.
22
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.3.4.2 High-Accuracy Power Sense Amplifier (PSYS)
The charger monitors total system power. During forward mode, the input adapter powers system. The ratio of
PSYS current and total power KPSYS can be programmed in REG0x30[9] with default 1 μA/W. The input and
charge sense resistors (RAC and RSR) are programmed in REG0x30[11:10]. PSYS voltage can be calculated
with Equation 1 where IIN>0 when adapter is in forward charging, and IBAT>0 when the battery is in discharge
when the battery is in discharge.
VPSYS RPSYS u KPSYS (VACP u IIN VBAT u IBAT )
(1)
For proper PSYS functionality, RAC and RSR values are limited to 10mΩ and 20mΩ.
8.3.5 Input Source Dynamic Power Manage
Refer to Input Current and Input Voltage Registers for Dynamic Power Management.
8.3.6 Two-Level Adapter Current Limit (Peak Power Mode)
Usually adapter can supply current higher than DC rating for a few milliseconds to tens of milliseconds. The
charger employs two-level input current limit, or peak power mode, to fully utilize the overloading capability and
minimize battery discharge during CPU turbo mode. Peak power mode is enabled in REG0x31[13]
(EN_PKPWR_IDPM) or REG0x31[12] (EN_PKPWR_VSYS). The DC current limit, or ILIM1, is the same as
adapter DC current, set in REG0x3F(). The overloading current, or ILIM2, is set in REG0x33[15:11], as a
percentage of ILIM1.
When the charger detects input current surge and battery discharge due to load transient, it applies ILIM2 for
TOVLD in REG0x31[15:14], first, and then ILIM1 for up to TMAX – TOVLD time. TMAX is programmed in REG0x31[9:8].
After TMAX, if the load is still high, another peak power cycle starts. Charging is disabled during TMAX,; once TMAX,
expires, charging continues. If TOVLD is programmed higher than TMAX, then peak power mode is always on.
ICRIT
ILIM2
ILIM1
TOVLD
TOVLD
TMAX
IVBUS
ISYS
IBAT
Battery Discharge
PROCHOT
Figure 8. Two-Level Adapter Current Limit Timing Diagram
8.3.7 Processor Hot Indication
When CPU is running turbo mode, the system peak power may exceed available power from adapter and battery
together. The adapter current and battery discharge peak current, or system voltage drop is an indication that
system power is too high. The charger processor hot function monitors these events, and PROCHOT pulse is
asserted. Once CPU receives PROCHOT pulse from charger, it slows down to reduce the system power. The
processor hot function monitors these events, and PROCHOT pulse is asserted.
The PROCHOT triggering events include:
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
23
bq25708
SLUSCU2 – NOVEMBER 2017
•
•
•
•
•
•
•
www.ti.com
ICRIT: adapter peak current, as 110% of ILIM2
INOM: adapter average current (110% of input current limit)
IDCHG: battery discharge current
VSYS: system voltage on VSYS
Adapter Removal: upon adapter removal (CHRG_OK pin HIGH to LOW)
Battery Removal: upon battery removal (CELL_BATPRESZ pin goes LOW)
CMPOUT: Independent comparator output (CMPOUT pin HIGH to LOW)
The threshold of ICRIT, IDCHG or VSYS, and the deglitch time of ICRIT, INOM, IDCHG or CMPOUT are
programmable through SMBus. Each triggering event can be individually enabled in REG0x34[6:0]. When any
event in PROCHOT profile is triggered, PROCHOT is asserted low for minimum 10 ms programmable in
0x33[4:3]. At the end of the 10 ms, if the PROCHOT event is still active, the pulse gets extended.
ICRIT
IADP
Adjustable
Deglitch
1.05V
INOM
IDCHG
50 Ω
PROCHOT
Ref_DCHG
10 ms
Debounce
Ref
10 ms
VSRP
<0.3V
20 µs
Deglitch
CELL_BATPRESZ
(one shot on pin falling edge)
CMPOUT
CHRG_OK
(one shot on pin falling edge)
Copyright © 2017, Texas Instruments Incorporated
Figure 9. PROCHOT Profile
8.3.7.1 PROCHOT During Low Power Mode
During low power mode (REG0x12[15]=1), the charger offers a low quiescent current (~150 uA) Low power
PROCHOT function uses the independent comparator to monitor battery discharge current and system voltage,
and assert PROCHOT to CPU.
Below lists the register setting to enable PROCHOT during low power mode.
• REG0x12[15]=1
• REG0x34[5:0]=000000
• REG0x30[6:4]=100
• Independent comparator threshold is always 1.2V
• When REG0x30[14]=1, charger monitors discharge current. Connect CMPIN to voltage proportional to IBAT
pin. PROCHOT triggers from HIGH to LOW when CMPIN voltage falls below 1.2V.
• When REG0x30[13]=1, charger monitors system voltage. Connect CMPIN to voltage proportional to system.
PROCHOT triggers from HIGH to LOW when CMPIN voltage rises above 1.2V.
24
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
PROCHOT
1.2 V
Voltage v VSYS
Independent
Comparator
CMPIN
Voltage v (VSRN ± VSRP)
bq25708
Copyright © 2017, Texas Instruments Incorporated
Figure 10. PROCHOT Low Power Mode Implementation
8.3.7.2 PROCHOT Status
REG0x21[6:0] reports which event in the profile triggers PROCHOT by setting the corresponding bit to 1. The
status bit can be reset back to 0 after it is read by host, and current PROCHOT event is no longer active.
Assume there are two PROCHOT events, event A and event B. Event A triggers PROCHOT first, but event B is
also active. Both status bits will be HIGH. At the end of the 10ms PROCHOT pulse, if PROCHOT is still active
(either by A or B), the PROCHOT pulse is extended.
8.3.8 Device Protection
8.3.8.1
Watchdog Timer
The charger includes watchdog timer to terminate charging if the charger does not receive a write
MaxChargeVoltage() or write ChargeCurrent() command within 175 s (adjustable via REG0x12[14:13]). When
watchdog timeout occurs, all register values are kept unchanged except ChargeCurrent() resets to zero. Battery
charging is suspended. Write MaxChargeVoltage() or write ChargeCurrent() commands must be re-sent to reset
watchdog timer and resume charging. Writing REG0x12[14:13] = 00 to disable watchdog timer also resumes
charging.
8.3.8.2
Input Overvoltage Protection (ACOV)
The charger has fixed ACOV voltage. When VBUS pin voltage is higher than ACOV, it is considered as adapter
over voltage. CHRG_OK will be pulled low, and converter will be disabled. As system falls below battery voltage,
BATFET will be turned on. When VBUS pin voltage falls below ACOV, it is considered as adapter voltage returns
back to normal voltage. CHRG_OK will be pulled high by external pull up resistor. The converter will resume if
enable conditions are valid.
8.3.8.3
Input Overcurrent Protection (ACOC)
If the input current exceeds the 1.25× or 2× (REG0x31[2]) of ILIM2_VTH (REG0x33[15:11]) set point, converter
stops switching. After 300 ms, converter will start switching again.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
25
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.3.8.4 System Overvoltage Protection (SYSOVP)
When the converter starts up, the bq25708 reads CELL pin configuration and sets MaxChargeVoltage() and
SYSOVP threshold (1s – 5 V, 2s – 12 V, 3s/4s – 19.5 V). Before REGx15() is written by host, the battery
configuration will change with CELL pin voltage. When SYSOVP happens, the device latches off the converter.
REG20[4] is set as 1. The user can clear the latch-off by either writing 0 to SYSOVP bit or removing and
plugging in adapter again. After the latch-off is cleared, converter starts again.
8.3.8.5
Battery Overvoltage Protection (BATOVP)
Battery over-voltage may happen when battery is removed during charging or the user plugs in a wrong battery.
The BATOVP threshold is 104% (1 s) or 102% (2 s to 4 s) of regulation voltage set in REG0x15().
8.3.8.6
Battery Short
If BAT voltage falls below SYSMIN during charging, the maximum current is limited to 384 mA.
8.3.8.7 Thermal Shutdown (TSHUT)
The WQFN package has low thermal impedance, which provides good thermal conduction from the silicon to the
ambient, to keep junction temperatures low. As added level of protection, the charger converter turns off for selfprotection whenever the junction temperature exceeds the 155°C. The charger stays off until the junction
temperature falls below 135°C. During thermal shut down, the LDO current limit is reduced to 16 mA and REGN
LDO stays off. When the temperature falls below 135°C, charge can be resumed with soft start.
8.4 Device Functional Modes
8.4.1 Forward Mode
When input source is connected to VBUS, bq25708 is in forward mode to regulate system and charge battery.
8.4.1.1 System Voltage Regulation with Narrow VDC Architecture
The bq25708 employs Narrow VDC architecture (NVDC) with BATFET separating system from battery. The
minimum system voltage is set by MinSystemVoltage(). Even with a deeply depleted battery, the system is
regulated above the minimum system voltage.
When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode).
As the battery voltage rises above the minimum system voltage, BATFET is fully on when charging or in
supplement mode and the voltage difference between the system and battery is the VDS of BATFET. System
voltage is regulated 160 mV above battery voltage when BATFET is off (no charging or no supplement current).
See System Voltage Regulation for details on system voltage regulation and register programming.
8.4.1.2 Battery Charging
The bq25708 charges 1-4 cell battery in constant current (CC), and constant voltage (CV) mode. Based on
CELL_BATPREZ pin setting, the charger sets default battery voltage 4.2V/cell to ChargeVoltage(), or
REG0x15(). According to battery capacity, the host programs appropriate charge current to ChargeCurrent(), or
REG0x14(). When battery is full or battery is not in good condition to charge, host terminates charge by setting
REG0x12[0] to 1, or setting ChargeCurrent() to zero.
See Feature Description for details on register programming.
26
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.5 Programming
The charger supports battery-charger commands that use either Write-Word or Read-Word protocols, as
summarized in SMBus Write-Word and Read-Word Protocols. The SMBUS address is 12h (0001001_X), where
X is the read/write bit. The ManufacturerID and DeviceID registers are assigned identify the charger device. The
ManufacturerID register command always returns 40h.
8.5.1 SMBus Interface
The bq25700 device operates as a slave, receiving control inputs from the embedded controller host through the
SMBus interface. The bq25700 device uses a simplified subset of the commands documented in System
Management Bus Specification V1.1, which can be downloaded from www.smbus.org. The bq25700 device uses
the SMBus read-word and write-word protocols (shown in Table 4 and Table 5) to communicate with the smart
battery. The bq25700 device performs only as a SMBus slave device with address 0b00010010 (0x12H) and
does not initiate communication on the bus. In addition, the bq25700 device has two identification registers, a 16bit device ID register (0xFFH) and a 16-bit manufacturer ID register (0xFEH).
SMBus communication starts when VCC is above V(UVLO).
The data (SDA) and clock (SCL) pins have Schmitt-trigger inputs that can accommodate slow edges. Choose
pullup resistors (10 kΩ) for SDA and SCL to achieve rise times according to the SMBus specifications.
Communication starts when the master signals a start condition, which is a high-to-low transition on SDA, while
SCL is high. When the master has finished communicating, the master issues a stop condition, which is a low-tohigh transition on SDA, while SCL is high. The bus is then free for another transmission. Figure 11 and Figure 12
show the timing diagram for signals on the SMBus interface. The address byte, command byte, and data bytes
are transmitted between the start and stop conditions. The SDA state changes only while SCL is low, except for
the start and stop conditions. Data is transmitted in 8-bit bytes and is sampled on the rising edge of SCL. Nine
clock cycles are required to transfer each byte in or out of the bq25708 device because either the master or the
slave acknowledges the receipt of the correct byte during the ninth clock cycle. The bq25708 supports the
charger commands listed in Table 4.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
27
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Programming (continued)
8.5.1.1 SMBus Write-Word and Read-Word Protocols
Table 4. Write-Word Format
S
(1) (2)
(1)
(2)
(3)
(4)
(5)
(6)
SLAVE
ADDRESS (1)
(1) (3)
W
ACK
COMMAND
BYTE (1)
ACK
7 bits
1b
MSB LSB
0
1b
8 bits
0
MSB LSB
(4) (5)
LOW DATA
BYTE (1)
ACK
1b
8 bits
0
MSB LSB
(4) (5)
HIGH DATA
BYTE (1)
ACK
1b
8 bits
1b
0
MSB LSB
0
(4) (5)
P
(4) (5)
(1) (6)
Master to slave
S = Start condition or repeated start condition
W = Write bit (logic-low)
Slave to master (shaded gray)
ACK = Acknowledge (logic-low)
P = Stop condition
Table 5. Read-Word Format
S (1)
(2)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
W
ACK COMMAND ACK S (1)
SLAVE
R (1) ACK LOW DATA ACK
(4) (5)
(4) (5)
(2)
(1) (5)
BYTE (1)
ADDRESS (1) (6) (4) (5)
BYTE (4)
SLAVE
ADDRESS (1)
(1) (3)
7 bits
1b
1b
8 bits
1b
7 bits
1b
1b
8 bits
MSB LSB
0
0
MSB LSB
0
MSB LSB
1
0
MSB LSB
HIGH DATA
BYTE (4)
NACK
1b
8 bits
1b
0
MSB LSB
1
(1) (7)
P
(1) (8)
Master to slave
S = Start condition or repeated start condition
W = Write bit (logic-low)
Slave to master (shaded gray)
ACK = Acknowledge (logic-low)
R = Read bit (logic-high)
NACK = Not acknowledge (logic-high)
P = Stop condition
8.5.1.2 Timing Diagrams
A
B
C
D
E
F
G
H
I J
K
L
M
tLOW tHIGH
SMBCLK
SMBDATA
tSU:STA tHD:STA
tSU:DAT tHD:DAT
tHD:DAT
tSU:STO tBUF
A = Start condition
H = LSB of data clocked into slave
B = MSB of address clocked into slave
I = Slave pulls SMBDATA line low
C = LSB of address clocked into slave
J = Acknowledge clocked into master
D = R/W bit clocked into slave
K = Acknowledge clock pulse
E = Slave pulls SMBDATA line low
L = Stop condition, data executed by slave
F = ACKNOWLEDGE bit clocked into master
M = New start condition
G = MSB of data clocked into slave
Figure 11. SMBus Write Timing
28
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
A
B
C
D
E
F
G
H
I
J
K
tLOW tHIGH
SMBCLK
SMBDATA
tSU:STA tHD:STA
tHD:DAT
tSU:DAT
A = START CONDITION
tSU:DAT
E = SLAVE PULLS SMBDATA LINE LOW
tSU:STO tBUF
I = ACKNOWLEDGE CLOCK PULSE
A = Start condition
G = MSB of data clocked into master
B = MSB of address clocked into slave
H = LSB of data clocked into master
C = LSB of address clocked into slave
I = Acknowledge clock pulse
D = R/W bit clocked into slave
J = Stop condition
E = Slave pulls SMBDATA line low
K = New start condition
F = ACKNOWLEDGE bit clocked into master
Figure 12. SMBus Read Timing
8.6 Register Map
Table 6. Charger Command Summary
SMBus
ADDR
REGISTER NAME
TYPE
DESCRIPTION
LINKS
12h
ChargeOption0()
R/W
Charge Option 0
Go
14h
ChargeCurrent()
R/W
7-bit charge current setting
LSB 64 mA, Range 8128 mA
Go
15h
MaxChargeVoltage()
R/W
11-bit charge voltage setting
LSB 16 mV, Default: 1S-4192mV, 2S-8400mV,
3S-12592mV, 4S-16800mV
Go
30h
ChargeOption1()
R/W
Charge Option 1
Go
31h
ChargeOption2()
R/W
Charge Option 2
Go
32h
ChargeOption3()
R/W
Charge Option 3
Go
33h
ProchotOption0()
R/W
PROCHOT Option 0
Go
34h
ProchotOption1()
R/W
PROCHOT Option 1
Go
35h
ADCOption()
R/W
ADC Option
Go
20h
ChargerStatus()
R
Charger Status
Go
21h
ProchotStatus()
R
Prochot Status
Go
22h
IIN_DPM()
R
7-bit input current limit in use
LSB: 50mA, Range: 50mA-6400mA
Go
23h
ADCVBUS/PSYS()
R
8-bit digital output of input voltage,
8-bit digital output of system power
PSYS: Full range: 3.06V, LSB: 12mV
VBUS: Full range: 3.2V-19.52V, LSB 64mV
Go
24h
ADCIBAT()
R
8-bit digital output of battery charge current,
8-bit digital output of battery discharge current
ICHG: Full range 8.128A, LSB 64mA
IDCHG: Full range: 32.512A, LSB: 256mA
Go
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
29
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Register Map (continued)
Table 6. Charger Command Summary (continued)
SMBus
ADDR
REGISTER NAME
TYPE
DESCRIPTION
LINKS
25h
ADCIINCMPIN()
R
8-bit digital output of input current,
8-bit digital output of CMPIN voltage
POR State - IIN: Full range: 12.75A, LSB 50mA
CMPIN: Full range 3.06V, LSB: 12mV
Go
26h
ADCVSYSVBAT()
R
8-bit digital output of system voltage,
8-bit digital output of battery voltage
VSYS: Full range: 2.88V-19.2V, LSB: 64mV
VBAT: Full range : 2.88V-19.2V, LSB 64mV
Go
3Bh
Reserved
R/W
3Ch
Reserved
R/W
3Dh
InputVoltage()
R/W
8-bit input voltage setting
LSB 64mV, Range: 3200 mV – 19520 mV
Go
3Eh
MinSystemVoltage()
R/W
6-Bit minimum system voltage setting
LSB: 256mV, Range: 1024mV-16182mV
Default: 1S-3.584V, 2S-6.144V, 3S-9.216V, 4S12.288V
Go
3Fh
IIN_HOST()
R/W
6-bit Input current limit set by host
LSB: 50mA, Range: 50mA-6400mA
Go
FEh
ManufacturerID()
R
Manufacturer ID - 0x0040H
Go
FFh
DeviceID()
R
Device ID
Go
30
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.1 Setting Charge and PROCHOT Options
8.6.1.1 ChargeOption0 Register (SMBus address = 12h) [reset = E20Eh]
Figure 13. ChargeOption0 Register (SMBus address = 12h) [reset = E20Eh]
15
EN_LWPWR
14
13
12
IDPM_AUTO_
DISABLE
R/W
11
Reserved
10
EN_OOA
9
PWM_FREQ
8
Reserved
R/W
R/W
R/W
R/W
5
EN_LEARN
R/W
4
IADPT_GAIN
R/W
3
IBAT_GAIN
R/W
2
EN_LDO
R/W
1
EN_IDPM
R/W
0
CHRG_INHIBIT
R/W
WDTMR_ADJ
R/W
R/W
7
6
Reserved
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 7. ChargeOption0 Register (SMBus address = 12h) Field Descriptions
SMBus
BIT
15
FIELD
TYPE
RESET
DESCRIPTION
EN_LWPWR
R/W
1b
Low Power Mode Enable
0b: Disable Low Power Mode. Device in performance mode with battery only.
The PROCHOT, current/power monitor buffer and comparator follow register
setting.
1b: Enable Low Power Mode. Device in low power mode with battery only for
lowest quiescent current. /PROCHOT, discharge current monitor buffer, power
monitor buffer and independent comparator are disabled. Independent
comparator can be enabled by setting either REG0X30()[14] or [13] to 1.
<default at POR>
14-13
WDTMR_ADJ
R/W
11b
WATCHDOG Timer Adjust
Set maximum delay between consecutive SMBus write of charge voltage or
charge current command.
If device does not receive a write on the REG0x15() or the REG0x14() within
the watchdog time period, the charger will be suspended by setting the
REG0x14() to 0 mA.
After expiration, the timer will resume upon the write of REG0x14(),
REG0x15() or REG0x12[14:13]. The charger will resume if the values are
valid.
00b: Disable Watchdog Timer
01b: Enabled, 5 sec
10b: Enabled, 88 sec
11b: Enable Watchdog Timer, 175 sec <default at POR>
12
IDPM_AUTO_
DISABLE
R/W
0b
IDPM Auto Disable
When CELL_BATPRESZ pin is LOW, the charger automatically disables the
IDPM function by setting EN_IDPM (REG0x12[1]) to 0. The host can enable
IDPM function later by writing EN_IDPM bit (REG0x12[1]) to 1.
0b: Disable this function. IDPM is not disabled when CELL_BATPRESZ goes
LOW. <default at POR>
1b: Enable this function. IDPM is disabled when CELL_BATPRESZ goes
LOW.
11
Reserved
R/W
10
EN_OOA
R/W
Reserved
0b
Out-of-Audio Enable
0b: No limit of PFM burst frequency <default at POR>
1b: Set minimum PFM burst frequency to above 25 kHz to avoid audio noise
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
31
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Table 7. ChargeOption0 Register (SMBus address = 12h) Field Descriptions (continued)
SMBus
BIT
9
FIELD
TYPE
RESET
DESCRIPTION
PWM_FREQ
R/W
1b
Switching Frequency
Two converter switching frequencies. One for small inductor and the other for
big inductor.
Currently, customer uses 800 kHz with 2.2 µH or 3.3 µH, and 1.2 MHz with 1
µH or 1.5 µH.
0b: 1.2 MHz
1b: 800 kHz <default at POR>
8
Reserved
R/W
0b
Reserved
Table 8. ChargeOption0 Register (SMBus address = 12h) Field Descriptions
SMBus
BIT
7-6
5
FIELD
TYPE
RESET
DESCRIPTION
Reserved
R/W
00b
Reserved
EN_LEARN
R/W
0b
LEARN function allows the battery to discharge while the adapter is present. It
calibrates the battery gas gauge over a complete discharge/charge cycle.
When the battery voltage is below battery depletion threshold, the system
switches back to adapter input by the host. When CELL_BATPRESZ pin is
LOW, the device exits LEARN mode and this bit is set back to 0.
0b: Disable LEARN Mode <default at POR>
1b: Enable LEARN Mode
4
IADPT_GAIN
R/W
0b
IADPT Amplifier Ratio
The ratio of voltage on IADPT and voltage across ACP and ACN.
0b: 20× <default at POR>
1b: 40×
3
IBAT_GAIN
R/W
1b
IBAT Amplifier Ratio
The ratio of voltage on IBAT and voltage across SRP and SRN
0b: 8×
1b: 16× <default at POR>
2
EN_LDO
R/W
1b
LDO Mode Enable
When battery voltage is below minimum system voltage (REG0x3E()), the
charger is in pre-charge with LDO mode enabled.
0b: Disable LDO mode, BATFET fully ON. Precharge current is set by battery
pack internal resistor. The system is regulated by the MaxChargeVoltage
register.
1b: Enable LDO mode, Precharge current is set by the ChargeCurrent register
and clamped below 384 mA (2 cell – 4 cell) or 2A (1 cell). The system is
regulated by the MinSystemVoltage register. <default at POR>
1
EN_IDPM
R/W
1b
IDPM Enable
Host writes this bit to enable IDPM regulation loop. When the IDPM is disabled
by the charger (refer to IDPM_AUTO_DISABLE), this bit goes LOW.
0b: IDPM disabled
1b: IDPM enabled <default at POR>
0
CHRG_INHIBIT
R/W
0b
Charge Inhibit
When this bit is 0, battery charging will start with valid values in the
MaxChargeVoltage register and the ChargeCurrent register.
0b: Enable Charge <default at POR>
1b: Inhibit Charge
32
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.1.2 ChargeOption1 Register (SMBus address = 30h) [reset = 211h]
Figure 14. ChargeOption1 Register (SMBus address = 30h) [reset = 211h]
15
EN_IBAT
R/W
14
13
EN_PROCHOT_LPWR
R/W
7
CMP_REF
6
CMP_POL
R/W
R/W
12
EN_PSYS
R/W
11
RSNS_RAC
R/W
10
RSNS_RSR
R/W
9
PSYS_RATIO
R/W
8
Reserved
R/W
4
3
FORCE_
LATCHOFF
R/W
2
Reserved
1
EN_SHIP_
DCHG
R/W
0
AUTO_
WAKEUP_EN
R/W
5
CMP_DEG
R/W
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 9. ChargeOption1 Register (SMBus address = 30h) Field Descriptions
SMBus
FIELD
BIT
15
EN_IBAT
TYPE
RESET
DESCRIPTION
R/W
0b
IBAT Enable
Enable the IBAT output buffer. In low power mode (REG0x12[15] = 1), IBAT
buffer is always disabled regardless of this bit value.
0b Turn off IBAT buffer to minimize Iq <default at POR>
1b: Turn on IBAT buffer
14-13
EN_PROCHOT
_LPWR
R/W
00b
Enable PROCHOT during battery only low power mode
With battery only, enable IDCHG or VSYS in PROCHOT with low power
consumption. Do not enable this function with adapter present. Refer to
PROCHOT During Low Power Mode for more details.
00b: Disable low power PROCHOT <default at POR>
01b: Enable IDCHG low power PROCHOT
10b: Enable VSYS low power PROCHOT
11b: Reserved
12
EN_PSYS
R/W
0b
PSYS Enable
Enable PSYS sensing circuit and output buffer (whole PSYS circuit). In low
power mode (REG0x12[15] = 1), PSYS sensing and buffer are always disabled
regardless of this bit value.
0b: Turn off PSYS buffer to minimize Iq <default at POR>
1b: Turn on PSYS buffer
11
RSNS_RAC
R/W
0b
Input sense resistor RAC
0b: 10 mΩ <default at POR>
1b: 20 mΩ
10
RSNS_RSR
R/W
0b
Charge sense resistor RSR
0b: 10 mΩ <default at POR>
1b: 20 mΩ
9
PSYS_RATIO
R/W
1b
PSYS Gain
Ratio of PSYS output current vs total input and battery power with 10-mΩ sense
resistor.
0b: 0.25 µA/W
1b: 1 µA/W <default at POR>
8
Reserved
R/W
0b
Reserved
Table 10. ChargeOption1 Register (SMBus address = 30h) Field Descriptions
SMBus
FIELD
BIT
7
CMP_REF
TYPE
RESET
DESCRIPTION
R/W
0b
Independent Comparator Internal Reference
0b: 2.3 V <default at POR>
1b: 1.2 V
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
33
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Table 10. ChargeOption1 Register (SMBus address = 30h) Field Descriptions (continued)
SMBus
FIELD
BIT
6
CMP_POL
TYPE
RESET
DESCRIPTION
R/W
0b
Independent Comparator Output Polarity
0b: When CMPIN is above internal threshold, CMPOUT is LOW (internal
hysteresis) <default at POR>
1b: When CMPIN is below internal threshold, CMPOUT is LOW (external
hysteresis)
5-4
CMP_DEG
R/W
01b
Independent Comparator Deglitch Time, only applied to the falling edge of
CMPOUT (HIGH → LOW).
00b: Independent comparator is disabled
01b: Independent comparator is enabled with output deglitch time 1 µs <default
at POR>
10b: Independent comparator is enabled with output deglitch time of 2 ms
11b: Independent comparator is enabled with output deglitch time of 5 sec
3
FORCE_LATCHOFF
R/W
0b
Force Power Path Off
When the independent comparator triggers, charger turns off Q1 and Q4 (same
as disable converter) so that the system is disconnected from the input source.
At the same time, CHRG_OK signal goes to LOW to notify the system.
0b: Disable this function <default at POR>
1b: Enable this function
2
Reserved
R/W
0b
Reserved
1
EN_SHIP_DCHG
R/W
0b
Discharge SRN for Shipping Mode
When this bit is 1, discharge SRN pin down below 3.8 V in 140 ms. When 140
ms is over, this bit is reset to 0.
0b: Disable shipping mode <default at POR>
1b: Enable shipping mode
0
AUTO_WAKEUP_EN
R/W
1b
Auto Wakeup Enable
When this bit is HIGH, if the battery is below minimum system voltage
(REG0x3E()), the device will automatically enable 128 mA charging current for
30 mins. When the battery is charged up above minimum system voltage, charge
will terminate and the bit is reset to LOW.
0b: Disable
1b: Enable <default at POR>
34
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.1.3 ChargeOption2 Register (SMBus address = 31h) [reset = 2B7]
Figure 15. ChargeOption2 Register (SMBus address = 31h) [reset = 2B7]
15
14
PKPWR_TOVLD_DEG
R/W
7
EN_EXTILIM
R/W
6
EN_ICHG
_IDCHG
R/W
13
EN_PKPWR
_IDPM
R/W
12
EN_PKPWR
_VSYS
R/W
11
PKPWR_
OVLD_STAT
R/W
10
PKPWR_
RELAX_STAT
R/W
9
8
PKPWR_TMAX[1:0]
5
Q2_OCP
4
ACX_OCP
3
EN_ACOC
2
ACOC_VTH
1
EN_BATOC
0
BATOC_VTH
R/W
R/W
R/W
R/W
R/W
R/W
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 11. ChargeOption2 Register (SMBus address = 31h) Field Descriptions
SMBus
BIT
15-14
FIELD
TYPE
RESET
DESCRIPTION
PKPWR_
TOVLD_DEG
R/W
00b
Input Overload time in Peak Power Mode
00b: 1 ms <default at POR>
01b: 2 ms
10b: 10 ms
11b: 20 ms
13
EN_PKPWR_IDPM
R/W
0b
Enable Peak Power Mode triggered by input current overshoot
If REG0x31[13:12] are 00b, peak power mode is disabled. Upon
adapter removal, the bits are reset to 00b.
0b: Disable peak power mode triggered by input current overshoot
<default at POR>
1b: Enable peak power mode triggered by input current overshoot.
12
EN_PKPWR_VSYS
R/W
0b
Enable Peak Power Mode triggered by system voltage under-shoot
If REG0x31[13:12] are 00b, peak power mode is disabled. Upon
adapter removal, the bits are reset to 00b.
0b: Disable peak power mode triggered by system voltage under-shoot
<default at POR>
1b: Enable peak power mode triggered by system voltage under-shoot.
11
PKPWR_
OVLD_STAT
R/W
0b
Indicator that the device is in overloading cycle. Write 0 to get out of
overloading cycle.
0b: Not in peak power mode. <default at POR>
1b: In peak power mode.
10
PKPWR_
RELAX_STAT
R/W
0b
Indicator that the device is in relaxation cycle. Write 0 to get out of
relaxation cycle.
0b: Not in relaxation cycle. <default at POR>
1b: In relaxation mode.
9-8
PKPWR_
TMAX[1:0]
R/W
10b
Peak power mode overload and relax cycle time.
When REG0x31[15:14] is programmed longer than REG0x31[9:8],
there is no relax time.
00b: 5 ms
01b: 10 ms
10b: 20 ms <default at POR>
11b: 40 ms
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
35
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Table 12. ChargeOption2 Register (SMBus address = 31h) Field Descriptions
SMBus
BIT
7
FIELD
TYPE
RESET
DESCRIPTION
EN_EXTILIM
R/W
1b
Enable ILIM_HIZ pin to set input current limit
0b: Input current limit is set by REG0x3F.
1b: Input current limit is set by the lower value of ILIM_HIZ pin and
REG0x3F. <default at POR>
6
EN_ICHG
_IDCHG
R/W
0b
5
Q2_OCP
R/W
1b
0b: IBAT pin as discharge current. <default at POR>
1b: IBAT pin as charge current.
Q2 OCP threshold by sensing Q2 VDS
0b: 300 mV
1b: 500 mV <default at POR>
4
ACX_OCP
R/W
1b
Input current OCP threshold by sensing ACP-ACN.
0b: 150 mV
1b: 280 mV <default at POR>
3
EN_ACOC
R/W
0b
ACOC Enable
Input overcurrent (ACOC) protection by sensing the voltage across
ACP and ACN. Upon ACOC (after 100-µs blank-out time), converter is
disabled.
0b: Disable ACOC <default at POR>
1b: ACOC threshold 125% or 200% ICRIT
2
ACOC_VTH
R/W
1b
ACOC Limit
Set MOSFET OCP threshold as percentage of IDPM with current
sensed from RAC.
0b: 125% of ICRIT
1b: 200% of ICRIT <default at POR>
1
EN_BATOC
R/W
1b
BATOC Enable
Battery discharge overcurrent (BATOC) protection by sensing the
voltage across SRN and SRP. Upon BATOC, converter is disabled.
0b: Disable BATOC
1b: BATOC threshold 125% or 200% PROCHOT IDCHG <default at
POR>
0
BATOC_VTH
R/W
1b
Set battery discharge overcurrent threshold
PROCHOT battery discharge current limit.
as
percentage
of
0b: 125% of PROCHOT IDCHG
1b: 200% of PROCHOT IDCHG <default at POR>
36
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.1.4 ChargeOption3 Register (SMBus address = 32h) [reset = 0h]
Figure 16. ChargeOption3 Register (SMBus address = 32h) [reset = 0h]
15
EN_HIZ
14
RESET_REG
12
Reserved
R/W
13
RESET_
VINDPM
R/W
R/W
7
10
R/W
11
EN_ICO_MOD
E
R/W
6
5
4
3
2
9
Reserved
8
R/W
1
BATFETOFF_
HIZ
R/W
Reserved
R/W
0
Reserved
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 13. ChargeOption3 Register (SMBus address = 32h) Field Descriptions
SMBus
FIELD
BIT
15
EN_HIZ
TYPE
RESET
DESCRIPTION
R/W
0b
Device Hi-Z Mode Enable
When the charger is in Hi-Z mode, the device draws minimal quiescent
current. With VBUS above UVLO. REGN LDO stays on, and system
powers from battery.
0b: Device not in Hi-Z mode <default at POR>
1b: Device in Hi-Z mode
14
RESET_REG
R/W
0b
Reset Registers
All the registers go back to the default setting except the VINDPM
register.
0b: Idle <default at POR>
1b: Reset all the registers to default values. After reset, this bit goes back
to 0.
13
RESET_VINDPM
R/W
0b
Reset VINDPM Threshold
0b: Idle
1b: Converter is disabled to measure VINDPM threshold. After VINDPM
measurement is done, this bit goes back to 0 and converter starts.
12
Reserved
R/W
11
EN_ICO_MODE
R/W
Reserved
0b
Enable ICO Algorithm
0b: Disable ICO algorithm. <default at POR>
1b: Enable ICO algorithm.
10-8
Reserved
R/W
000b
Reserved
Table 14. ChargeOption3 Register (SMBus address = 32h) Field Descriptions
SMBus
FIELD
BIT
7-2
1
TYPE
RESET
DESCRIPTION
Reserved
R/W
000000b
Reserved
BATFETOFF_
HIZ
R/W
0b
Control BATFET during HIZ mode.
0b: BATFET on during Hi-Z <default at POR>
1b: BATFET off during Hi-Z
0
Reserved
R/W
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
37
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.1.5 ProchotOption0 Register (SMBus address = 33h) [reset = 04A54h]
Figure 17. ProchotOption0 Register (SMBus address = 33h) [reset = 04A54h]
15-11
ILIM2_VTH
R/W
7-6
VSYS_VTH
R/W
5
EN_PROCHOT
_EXT
R/W
10-9
ICRIT_DEG
R/W
4-3
PROCHOT_WIDTH
R/W
2
PROCHOT_
CLEAR
R/W
8
Reserved
R/W
1
INOM_DEG
0
Reserved
R/W
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 15. ProchotOption0 Register (SMBus address = 33h) Field Descriptions
SMBus
FIELD
BIT
15-11
ILIM2_VTH
TYPE
RESET
DESCRIPTION
R/W
01001b
ILIM2 Threshold
5 bits, percentage of IDPM in 0x3FH. Measure current between ACP and ACN.
Trigger when the current is above this threshold:
00001b - 11001b: 110% - 230%, step 5%
11010b - 11110b: 250% - 450%, step 50%
11111b: Out of Range (Ignored)
Default 150%, or 01001
10-9
ICRIT_DEG
R/W
01b
ICRIT Deglitch time
ICRIT threshold is set to be 110% of
ILIM2.
Typical ICRIT deglitch time to trigger PROCHOT.
00b: 15 µs
01b: 100 µs <default at POR>
10b: 400 µs (max 500 us)
11b: 800 µs (max 1 ms)
8
Reserved
R/W
0b
Reserved
Table 16. ProchotOption0 Register (SMBus address = 33h) Field Descriptions
SMBus
FIELD
BIT
7-6
VSYS_VTH
TYPE
RESET
DESCRIPTION
R/W
01b
VSYS Threshold
Measure on VSYS with fixed 20-µs deglitch time. Trigger when SYS pin voltage is
below the threshold.
00b: 5.75 V (2-4 s) or 2.85 V (1 s)
01b: 6 V (2-4 s) or 3.1 V (1 s) <default at POR>
10b: 6.25 V (2-4 s) or 3.35 V (1 s)
11b: 6.5 V (2-4 s) or 3.6 V (1 s)
5
EN_PROCHOT
_EXT
R/W
0b
PROCHOT Pulse Extension Enable
When pulse extension is enabled, keep the PROCHOT pin voltage LOW until host
writes 0x33[2] = 0.
0b: Disable pulse extension <default at POR>
1b: Enable pulse extension
4-3
PROCHOT
_WIDTH
R/W
10b
PROCHOT Pulse Width
Minimum PROCHOT pulse width when REG0x33[5] = 0
00b: 100 µs
01b: 1 ms
10b: 10 ms <default at POR>
11b: 5 ms
38
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Table 16. ProchotOption0 Register (SMBus address = 33h) Field Descriptions (continued)
SMBus
FIELD
BIT
2
PROCHOT
_CLEAR
TYPE
RESET
DESCRIPTION
R/W
1b
PROCHOT Pulse Clear
Clear PROCHOT pulse when 0x3C[5] = 1.
0b: Clear PROCHOT pulse and drive PROCHOT pin HIGH.
1b: Idle <default at POR>
1
INOM_DEG
R/W
0b
INOM Deglitch Time
INOM is always 10% above IDPM in 0x3FH. Measure current between ACP and
ACN.
Trigger when the current is above this threshold.
0b: 1 ms (must be max) <default at POR>
1b: 50 ms (max 60 ms)
0
Reserved
R/W
0b
Reserved
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
39
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.1.6 ProchotOption1 Register (SMBus address = 34h) [reset = 8120h]
Figure 18. ProchotOption1 Register (SMBus address = 34h) [reset = 8120h]
15-10
IDCHG_VTH
R/W
7
Reserved
R/W
6
PROCHOT_PR
OFILE_IC
R/W
9-8
IDCHG_DEG
R/W
5
PP_ICRIT
4
PP_INOM
3
PP_IDCHG
2
PP_VSYS
1
PP_BATPRES
0
PP_ACOK
R/W
R/W
R/W
R/W
R/W
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 17. ProchotOption1 Register (SMBus address = 34h) Field Descriptions
SMBus
BIT
15-10
FIELD
TYPE
RESET
DESCRIPTION
IDCHG_VTH
R/W
000000b
IDCHG Threshold
6 bit, range, range 0 A to 32256 mA, step 512 mA. There is a 128 mA offset
measured current between SRN and SRP.
Trigger when the discharge current is above the threshold.
If the value is programmed to 000000b, PROCHOT is always triggered.
Default: 16384 mA or 100000
9-8
IDCHG_DEG
R/W
01b
IDCHG Deglitch Time
00b: 1.6 ms
01b: 100 µs <default at POR>
10b: 6 ms
11b: 12 ms
Table 18. ProchotOption1 Register (SMBus address = 34h) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
Reserved
R/W
0b
Reserved
6
PROCHOT
_PROFILE_COMP
R/W
0b
PROCHOT Profile
When all the REG0x34[6:0] bits are 0, PROCHOT function is disabled.
Bit6 Independent comparator
0b: disable <default at POR>
1b: enable
5
PROCHOT
_PROFILE_ICRIT
R/W
1b
4
PROCHOT
_PROFILE_INOM
R/W
0b
3
PROCHOT
_PROFILE_IDCHG
R/W
0b
2
PROCHOT
_PROFILE_VSYS
R/W
0b
1
PROCHOT
_PROFILE_BATPRES
R/W
0b
0b: disable
1b: enable <default at POR>
0b: disable <default at POR>
1b: enable
0b: disable <default at POR>
1b: enable
0b: disable <default at POR>
1b: enable
0b: disable <default at POR>
1b: enable (one-shot falling edge triggered)
If BATPRES is enabled in PROCHOT after the battery is removed, it will
immediately send out one-shot PROCHOT pulse.
40
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Table 18. ProchotOption1 Register (SMBus address = 34h) Field Descriptions (continued)
SMBus
BIT
0
FIELD
TYPE
RESET
DESCRIPTION
PROCHOT
_PROFILE_ACOK
R/W
0b
0b: disable <default at POR>
1b: enable (one-shot falling edge triggered)
ChargeOption0[15] = 0 to pull PROCHOT low after adapter removal.
If BATPRES is enabled in PROCHOT after the battery is removed, it will
immediately send out one-shot PROCHOT pulse.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
41
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.1.7 ADCOption Register (SMBus address = 35h) [reset = 2000h]
Figure 19. ADCOption Register (SMBus address = 35h) [reset = 2000h]
15
ADC_CONV
14
ADC_START
R/W
R/W
13
ADC_
FULLSCALE
R/W
7
EN_ADC_
CMPIN
R/W
6
EN_ADC_
VBUS
R/W
5
EN_ADC_
PSYS
R/W
12-8
Reserved
R/W
4
EN_ADC_
IIN
R/W
3
EN_ADC_
IDCHG
R/W
2
EN_ADC_
ICHG
R/W
1
EN_ADC_
VSYS
R/W
0
EN_ADC_
VBAT
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 19. ADCOption Register (SMBus address = 35h) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
15
ADC_CONV
R/W
0b
Typical ADC conversion time is 10 ms.
0b: One-shot update. Do one set of conversion updates to registers
REG0x23(), REG0x24(), REG0x25(), and REG0x26() after ADC_START =
1.
1b: Continuous update. Do a set of conversion updates to registers
REG0x23(), REG0x24(), REG0x25(), and REG0x26() every 1 sec.
14
ADC_START
R/W
0b
0b: No ADC conversion
1b: Start ADC conversion. After the one-shot update is complete, this bit
automatically resets to zero
13
ADC_
FULLSCALE
R/W
1b
ADC input voltage range. When input voltage is below 5V, or battery is 1S,
full scale 2.04V is recommended.
0b: 2.04 V
1b: 3.06 V <default at POR>
12-8
Reserved
R/W
00000b
Reserved
Table 20. ADCOption Register (SMBus address = 35h) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
EN_ADC_CMPIN
R/W
0b
0b: Disable <default at POR>
6
EN_ADC_VBUS
R/W
0b
5
EN_ADC_PSYS
R/W
0b
4
EN_ADC_IIN
R/W
0b
3
EN_ADC_IDCHG
R/W
0b
2
EN_ADC_ICHG
R/W
0b
1
EN_ADC_VSYS
R/W
0b
1b: Enable
0b: Disable <default at POR>
1b: Enable
0b: Disable <default at POR>
1b: Enable
0b: Disable <default at POR>
1b: Enable
0b: Disable <default at POR>
1b: Enable
0b: Disable <default at POR>
1b: Enable
0b: Disable <default at POR>
1b: Enable
0
EN_ADC_VBAT
R/W
0b
0b: Disable <default at POR>
1b: Enable
42
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.2 Charge and PROCHOT Status
8.6.2.1 ChargerStatus Register (SMBus address = 20h) [reset = 0000h]
Figure 20. ChargerStatus Register (SMBus address = 20h) [reset = 0000h]
15
AC_STAT
R
14
ICO_DONE
R
13
Reserved
R
12
IN_VINDPM
R
11
IN_IINDPM
R
10
IN_FCHRG
R
9
IN_PCHRG
R
8
Reserved
R
7
Fault ACOV
6
Fault BATOC
5
Fault ACOC
3
Reserved
2
Fault Latchoff
1
Reserved
0
Reserved
R
R
R
4
SYSOVP_
STAT
R
R
R
R
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 21. ChargerStatus Register (SMBus address = 20h) Field Descriptions
SMBus
BIT
15
FIELD
TYPE
RESET
DESCRIPTION
AC_STAT
R
0b
Input source status, same as CHRG_OK pin
0b: Input not present
1b: Input is present
14
ICO_DONE
R
0b
After the ICO routine is successfully executed, the bit goes 1.
0b: ICO is not complete
1b: ICO is complete
13
Reserved
R
0b
Reserved
12
IN_VINDPM
R
0b
0b: Charger is not in VINDPM during forward mode
11
IN_IINDPM
R
0b
1b: Charger is in VINDPM during forward mode
0b: Charger is not in IINDPM
1b: Charger is in IINDPM
10
IN_FCHRG
R
0b
0b: Charger is not in fast charge
1b: Charger is in fast charger
9
IN_PCHRG
R
0b
0b: Charger is not in pre-charge
1b: Charger is in pre-charge
8
Reserved
R
Reserved
Table 22. ChargerStatus Register (SMBus address = 20h) Field Descriptions
SMBus
BIT
7
FIELD
TYPE
RESET
DESCRIPTION
Fault ACOV
R
0b
The faults are latched until a read from host.
0b: No fault
1b: ACOV
6
Fault BATOC
R
0b
The faults are latched until a read from host.
0b: No fault
1b: BATOC
5
Fault ACOC
R
0b
The faults are latched until a read from host.
0b: No fault
1b: ACOC
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
43
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
Table 22. ChargerStatus Register (SMBus address = 20h) Field Descriptions (continued)
SMBus
BIT
4
FIELD
TYPE
RESET
DESCRIPTION
SYSOVP_STAT
R
0b
SYSOVP Status and Clear
When the SYSOVP occurs, this bit is HIGH. During the SYSOVP,
the converter is disabled.
After the SYSOVP is removed, the user must write a 0 to this bit or
unplug the adapter to clear the SYSOVP condition to enable the
converter again.
0b: Not in SYSOVP <default at POR>
1b: In SYSOVP. When SYSOVP is removed, write 0 to clear the
SYSOVP latch.
3
Reserved
R
0b
Reserved
2
Fault Latchoff
R
0b
The faults are latched until a read from host.
0b: No fault
1b: Latch off (REG0x30[3])
44
1
Reserved
R
Reserved
0
Reserved
R
Reserved
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.2.2 ProchotStatus Register (SMBus address = 21h) [reset = 0h]
Figure 21. ProchotStatus Register (SMBus address = 21h) [reset = 0h]
15-8
Reserved
R
7
Reserved
6
STAT_COMP
5
STAT_ICRIT
4
STAT_INOM
3
STAT_IDCHG
2
STAT_VSYS
R
R
R
R
R
R
1
STAT_Battery_
Removal
R
0
STAT_Adapter
_Removal
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 23. ProchotStatus Register (SMBus address = 21h) Field Descriptions
SMBus
BIT
15-8
FIELD
TYPE
RESET
DESCRIPTION
Reserved
R
0000000
0b
Reserved
Table 24. ProchotStatus Register (SMBus address = 21h) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
Reserved
R
0b
Reserved
6
STAT_COMP
R
0b
0b: Not triggered
1b: Triggered
5
STAT_ICRIT
R
0b
4
STAT_INOM
R
0b
3
STAT_IDCHG
R
0b
2
STAT_VSYS
R
0b
1
STAT_Battery_Removal
R
0b
0
STAT_Adapter_Removal
R
0b
0b: Not triggered
1b: Triggered
0b: Not triggered
1b: Triggered
0b: Not triggered
1b: Triggered
0b: Not triggered
1b: Triggered
0b: Not triggered
1b: Triggered
0b: Not triggered
1b: Triggered
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
45
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.3 ChargeCurrent Register (SMBus address = 14h) [reset = 0h]
To set the charge current, write a 16-bit ChargeCurrent() command (REG0x14()) using the data format listed in
Figure 22
With 10-mΩ sense resistor, the charger provides charge current range of 64 mA to 8.128 A, with a 64-mA step
resolution. Upon POR, ChargeCurrent() is 0 A when auto wakeup is not active. Any conditions for CHRG_OK low
except ACOV will reset ChargeCurrent() to zero. CELL_BATPRESZ going LOW (battery removal) will reset the
ChargeCurrent() register to 0 A.
Charge current is not reset in ACOC, TSHUT, power path latch off (REG0x30[1]), and SYSOVP.
A 0.1-µF capacitor between SRP and SRN for differential mode filtering is recommended; an optional 0.1-µF
capacitor between SRN and ground, and an optional 0.1-µF capacitor between SRP and ground for common
mode filtering. Meanwhile, the capacitance on SRP should not be higher than 0.1 µF in order to properly sense
the voltage across SRP and SRN for cycle-by-cycle current detection.
The SRP and SRN pins are used to sense voltage drop across RSR with default value of 10 mΩ. However,
resistors of other values can also be used. For a larger sense resistor, a larger sense voltage is given, and a
higher regulation accuracy; but, at the expense of higher conduction loss. A current sensing resistor value no
more than 20 mΩ is suggested.
Figure 22. ChargeCurrent Register With 10-mΩ Sense Resistor (SMBus address = 14h) [reset = 0h]
15
14
Reserved
13
12
Charge
Current, bit 6
R/W
11
Charge
Current, bit 5
R/W
10
Charge
Current, bit 4
R/W
9
Charge
Current, bit 3
R/W
8
Charge
Current, bit 2
R/W
5
Reserved
4
3
2
Reserved
1
0
R/W
7
Charge
Current, bit 1
R/W
6
Charge
Current, bit 0
R/W
R/W
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 25. Charge Current Register (14h) With 10-mΩ Sense Resistor (SMBus address = 14h) Field
Descriptions
SMBus
BIT
15-13
12
FIELD
TYPE
RESET
DESCRIPTION
Reserved
R/W
000b
Not used. 1 = invalid write.
Charge Current, bit 6
R/W
0b
0 = Adds 0 mA of charger current.
1 = Adds 4096 mA of charger current.
11
Charge Current, bit 5
R/W
0b
0 = Adds 0 mA of charger current.
1 = Adds 2048 mA of charger current.
10
Charge Current, bit 4
R/W
0b
0 = Adds 0 mA of charger current.
1 = Adds 1024 mA of charger current.
9
Charge Current, bit 3
R/W
0b
8
Charge Current, bit 2
R/W
0b
0 = Adds 0 mA of charger current.
1 = Adds 512 mA of charger current.
0 = Adds 0 mA of charger current.
1 = Adds 256 mA of charger current.
46
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Table 26. Charge Current Register (14h) With 10-mΩ Sense Resistor (SMBus address = 14h) Field
Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
Charge Current, bit 1
R/W
0b
0 = Adds 0 mA of charger current.
6
Charge Current, bit 0
R/W
0b
Reserved
R/W
000000b
1 = Adds 128 mA of charger current.
0 = Adds 0 mA of charger current.
1 = Adds 64 mA of charger current.
5-0
8.6.3.1
Not used. Value Ignored.
Battery Pre-Charge Current Clamp
During pre-charge, BATFET works in linear mode or LDO mode (default REG0x12[2] = 1). For 2-4 cell battery,
the system is regulated at minimum system voltage in REG0x3E() and the pre-charge current is clamped at 384
mA. For 1 cell battery, the pre-charge to fast charge threshold is 3V, and the pre-charge current is clamped at
384mA. However, the BATFET stays in LDO mode operation till battery voltage is above minimum system
voltage (~3.6V). During battery voltage from 3V to 3.6V, the fast charge current is clamped at 2A.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
47
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.4 MaxChargeVoltage Register (SMBus address = 15h) [reset value based on CELL_BATPRESZ pin
setting]
To set the output charge voltage, write a 16-bit ChargeVoltage register command (REG0x15()) using the data
format listed in Figure 23. The charger provides charge voltage range from 1.024 V to 19.200 V, with 16-mV step
resolution. Any write below 1.024 V or above 19.200 V is ignored.
Upon POR, REG0x15() is by default set as 4192 mV for 1 s, 8400 mV for 2 s, 12592 mV for 3 s or 16800 mV for
4 s. After CHRG_OK, if host writes REG0x14() before REG0x15(), the charge will start after the write to
REG0x14().If the battery is different from 4.2 V/cell, the host has to write to REG0x15() before REG0x14() for
correct battery voltage setting. Writing REG0x15() to 0 will set REG0x15() to default value on CELL_BATPRESZ
pin, and force REG0x14() to zero to disable charge.
The SRN pin is used to sense the battery voltage for voltage regulation and should be connected as close to the
battery as possible, and directly place a decoupling capacitor (0.1-µF recommended) as close to the device as
possible to decouple high frequency noise.
Figure 23. MaxChargeVoltage Register (SMBus address = 15h) [reset value based on CELL_BATPRESZ
pin setting]
15
14
13
12
11
10
9
8
Reserved
R/W
Max Charge
Voltage, bit 10
R/W
Max Charge
Voltage, bit 9
R/W
Max Charge
Voltage, bit 8
R/W
Max Charge
Voltage, bit 7
R/W
Max Charge
Voltage, bit 6
R/W
Max Charge
Voltage, bit 5
R/W
Max Charge
Voltage, bit 4
R/W
7
Max Charge
Voltage, bit 3
R/W
6
Max Charge
Voltage, bit 2
R/W
5
Max Charge
Voltage, bit 1
R/W
4
Max Charge
Voltage, bit 0
R/W
3
2
1
0
Reserved
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 27. MaxChargeVoltage Register (SMBus address = 15h) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
15
Reserved
R/W
0b
Not used. 1 = invalid write.
14
Max Charge Voltage, bit 10
R/W
0b
0 = Adds 0 mV of charger voltage.
13
Max Charge Voltage, bit 9
R/W
0b
12
Max Charge Voltage, bit 8
R/W
0b
11
Max Charge Voltage, bit 7
R/W
0b
10
Max Charge Voltage, bit 6
R/W
0b
1 = Adds 16384 mV of charger voltage.
0 = Adds 0 mV of charger voltage.
1 = Adds 8192 mV of charger voltage
0 = Adds 0 mV of charger voltage.
1 = Adds 4096 mV of charger voltage.
0 = Adds 0 mV of charger voltage.
1 = Adds 2048 mV of charger voltage.
0 = Adds 0 mV of charger voltage.
1 = Adds 1024 mV of charger voltage.
9
Max Charge Voltage, bit 5
R/W
0b
0 = Adds 0 mV of charger voltage.
1 = Adds 512 mV of charger voltage.
8
Max Charge Voltage, bit 4
R/W
0b
0 = Adds 0 mV of charger voltage.
1 = Adds 256 mV of charger voltage.
48
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Table 28. MaxChargeVoltage Register (SMBus address = 15h) Field Descriptions
SMBus
BIT
7
FIELD
TYPE
RESET
DESCRIPTION
Max Charge Voltage, bit 3
R/W
0b
0 = Adds 0 mV of charger voltage.
1 = Adds 128 mV of charger voltage.
6
Max Charge Voltage, bit 2
R/W
0b
0 = Adds 0 mV of charger voltage.
1 = Adds 64 mV of charger voltage.
5
Max Charge Voltage, bit 1
R/W
0b
0 = Adds 0 mV of charger voltage.
1 = Adds 32 mV of charger voltage.
4
Max Charge Voltage, bit 0
R/W
0b
Reserved
R/W
0000b
0 = Adds 0 mV of charger voltage.
1 = Adds 16 mV of charger voltage.
3-0
Not used. Value Ignored.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
49
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.5 MinSystemVoltage Register (SMBus address = 3Eh) [reset value based on CELL_BATPRESZ pin
setting]
To set the minimum system voltage, write a 16-bit MinSystemVoltage register command (REG0x3E()) using the
data format listed in Figure 25. The charger provides minimum system voltage range from 1.024 V to 16.128 V,
with 256-mV step resolution. Any write below 1.024 V or above 16.128 V is ignored. Upon POR, the
MinSystemVoltage register is 3.584 V for 1 S, 6.144 V for 2 S and 9.216 V for 3 S, and 12.288 V for 4 S.
Figure 24. MinSystemVoltage Register (SMBus address = 3Eh) [reset value based on CELL_BATPRESZ
pin setting]
15
14
13
Min System
Voltage, bit 5
R/W
12
Min System
Voltage, bit 4
R/W
11
Min System
Voltage, bit 3
R/W
10
Min System
Voltage, bit 2
R/W
9
Min System
Voltage, bit 1
R/W
8
Min System
Voltage, bit 0
R/W
6
5
4
3
2
1
0
Reserved
R/W
7
Reserved
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 29. MinSystemVoltage Register (SMBus address = 3Eh) Field Descriptions
SMBus
BIT
15-14
13
FIELD
TYPE
RESET
DESCRIPTION
Reserved
R/W
00b
Not used. 1 = invalid write.
Min System Voltage, bit 5
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 8192 mV of system voltage.
12
Min System Voltage, bit 4
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 4096mV of system voltage.
11
Min System Voltage, bit 3
R/W
0b
10
Min System Voltage, bit 2
R/W
0b
9
Min System Voltage, bit 1
R/W
0b
8
Min System Voltage, bit 0
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 2048 mV of system voltage.
0 = Adds 0 mV of system voltage.
1 = Adds 1024 mV of system voltage.
0 = Adds 0 mV of system voltage.
1 = Adds 512 mV of system voltage.
0 = Adds 0 mV of system voltage.
1 = Adds 256 mV of system voltage.
Table 30. MinSystemVoltage Register (SMBus address = 3Eh) Field Descriptions
SMBus
BIT
7-0
50
FIELD
TYPE
RESET
DESCRIPTION
Reserved
R/W
0000000
0b
Not used. Value Ignored.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.5.1 System Voltage Regulation
The device employs Narrow VDC architecture (NVDC) with BATFET separating system from battery. The
minimum system voltage is set by REG0x3E(). Even with a deeply depleted battery, the system is regulated
above the minimum system voltage with BATFET.
When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode),
and the system is regulated above the minimum system voltage setting. As the battery voltage rises above the
minimum system voltage, BATFET is fully on when charging or in supplement mode and the voltage difference
between the system and battery is the VDS of BATFET. System voltage is regulated 160mV above battery
voltage when BATFET is off (no charging or no supplement current).
When BATFET is removed, the system node VSYS is shorted to SRP. Before the converter starts operation,
LDO mode needs to be disabled. The following sequence is required to configure charger without BATFET.
1. Before adapter plugs in, put the charger into HIZ mode. (either pull pin 6 ILIM_HIZ to ground, or set
REG0x32[15] to 1)
2. Set 0x12[2] to 0 to disable LDO mode.
3. Set 0x30[0] to 0 to disable auto-wakeup mode.
4. Check if battery voltage is properly programmed (REG0x15)
5. Set pre-charge/charge current (REG0x14)
6. Put the device out of HIZ mode. (Release ILIM_HIZ from ground and set REG0x32[15]=0).
In order to prevent any accidental SW mistakes, the host sets low input current limit (a few hundred milliamps)
when device is out of HIZ.
8.6.6 Input Current and Input Voltage Registers for Dynamic Power Management
The charger supports Dynamic Power Management (DPM). Normally, the input power source provides power for
the system load or to charge the battery. When the input current exceeds the input current setting, or the input
voltage falls below the input voltage setting, the charger decreases the charge current to provide priority to the
system load. As the system current rises, the available charge current drops accordingly towards zero. If the
system load keeps increasing after the charge current drops down to zero, the system voltage starts to drop. As
the system voltage drops below the battery voltage, the battery will discharge to supply the heavy system load.
8.6.6.1 Input Current Registers
To set the maximum input current limit, write a 16-bit IIN_HOST register command (REG0x3F()) using the data
format listed in Figure 25. When using a 10-mΩ sense resistor, the charger provides an input-current limit range
of 50 mA to 6400 mA, with 50-mA resolution. The default current limit is 3.3 A. Due to the USB current setting
requirement, the register setting specifies the maximum current instead of the typical current. Upon adapter
removal, the input current limit is reset to the default value of 3.3 A. The register setting is clamped at 50mA.
With code 00h and 01h, the input current limit settings are both 50mA.
The ACP and ACN pins are used to sense RAC with the default value of 10 mΩ. For a 20 mΩ sense resistor, a
larger sense voltage is given and a higher regulation accuracy, but at the expense of higher conduction loss.
Instead of using the internal DPM loop, the user can build up an external input current regulation loop and have
the feedback signal on the ILIM_HIZ pin.
VILIM _ HIZ = 1V + 40 ´ (VACP - VACN ) = 1 + 40 ´ IDPM ´ R AC
(2)
In order to disable ILIM_HIZ pin, the host can write to 0x31[7] to disable ILIM_HIZ pin, or pull ILIM_HIZ pin above
4 V.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
51
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.6.1.1 IIN_HOST Register With 10-mΩ Sense Resistor (SMBus address = 3Fh) [reset = 4000h]
Figure 25. IIN_HOST Register With 10-mΩ Sense Resistor (SMBus address = 3Fh) [reset = 4100h]
15
Reserved
R/W
14
Input Current
set by host, bit
6
R/W
13
Input Current
set by host, bit
5
R/W
12
Input Current
set by host, bit
4
R/W
11
Input Current
set by host, bit
3
R/W
10
Input Current
set by host, bit
2
R/W
9
Input Current
set by host, bit
1
R/W
8
Input Current
set by host, bit
0
R/W
7
6
5
4
3
2
1
0
Reserved
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 31. IIN_HOST Register With 10-mΩ Sense Resistor (SMBus address = 3Fh) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
15
Reserved
R
0b
Not used. 1 = invalid write.
14
Input Current set by host, bit 6
R
1b
0 = Adds 0 mA of input current.
1 = Adds 3200 mA of input current.
13
Input Current set by host, bit 5
R
0b
0 = Adds 0 mA of input current.
1 = Adds 1600 mA of input current.
12
Input Current set by host, bit 4
R
0b
11
Input Current set by host, bit 3
R
0b
10
Input Current set by host, bit 2
R
0b
9
Input Current set by host, bit 1
R
0b
8
Input Current set by host, bit 0
R
0b
0 = Adds 0 mA of input current.
1 = Adds 800 mA of input current.
0 = Adds 0 mA of input current.
1 = Adds 400 mA of input current.
0 = Adds 0 mA of input current.
1 = Adds 200 mA of input current.
0 = Adds 0 mA of input current.
1 = Adds 100 mA of input current.
0 = Adds 0 mA of input current.
1 = Adds 50 mA of input current.
Table 32. IIN_HOST Register With 10-mΩ Sense Resistor (SMBus address = 3Fh) Field Descriptions
SMBus
BIT
7-0
52
FIELD
TYPE
RESET
DESCRIPTION
Reserved
R
0000000
0b
Not used. Value Ignored.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.6.1.2 IIN_DPM Register With 10-mΩ Sense Resistor (SMBus address = 022h) [reset = 0h]
IIN_DPM register reflects the actual input current limit programmed in the register, either from host or from ICO.
After ICO, the current limit used by DPM regulation may differ from the IIN_HOST register settings. The actual
DPM limit is reported in REG0x22().
Figure 26. IIN_DPM Register With 10-mΩ Sense Resistor (SMBus address = 022h) [reset = 0h]
15
Reserved
R
14
13
12
11
10
9
8
Input Current in Input Current in Input Current in Input Current in Input Current in Input Current in Input Current in
DPM, bit 6
DPM, bit 5
DPM, bit 4
DPM, bit 3
DPM, bit 2
DPM, bit 1
DPM, bit 0
R
R
R
R
R
R
R
7
6
5
4
3
2
1
0
Reserved
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 33. IIN_DPM Register With 10-mΩ Sense Resistor (SMBus address = 022h) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
15
Reserved
R
0b
Not used. 1 = invalid write.
14
Input Current in DPM, bit 6
R
0b
0 = Adds 0 mA of input current.
13
Input Current in DPM, bit 5
R
0b
12
Input Current in DPM, bit 4
R
0b
11
Input Current in DPM, bit 3
R
0b
10
Input Current in DPM, bit 2
R
0b
1 = Adds 3200 mA of input current.
0 = Adds 0 mA of input current.
1 = Adds 1600 mA of input current.
0 = Adds 0 mA of input current.
1 = Adds 800mA of input current
0 = Adds 0 mA of input current.
1 = Adds 400 mA of input current.
0 = Adds 0 mA of input current.
1 = Adds 200 mA of input current.
9
Input Current in DPM, bit 1
R
0b
0 = Adds 0 mA of input current.
1 = Adds 100 mA of input current.
8
Input Current in DPM, bit 0
R
0b
0 = Adds 0 mA of input current.
1 = Adds 50 mA of input current.
Table 34. IIN_DPM Register With 10-mΩ Sense Resistor (SMBus address = 022h) Field Descriptions
SMBus
BIT
7-0
FIELD
TYPE
RESET
DESCRIPTION
Reserved
R
00000000b
Not used. Value Ignored.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
53
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.6.1.3 InputVoltage Register (SMBus address = 3Dh) [reset = VBUS-1.28V]
To set the input voltage limit, write a 16-bit InputVoltage register command (REG0x3D()) using the data format
listed in Figure 27.
If the input voltage drops more than the InputVoltage register allows, the device enters DPM and reduces the
charge current. The default offset voltage is 1.28 V below the no-load VBUS voltage. The DC offset is 3.2 V
(0000000).
Figure 27. InputVoltage Register (SMBus address = 3Dh) [reset = VBUS-1.28V]
15
14
13
Input Voltage,
bit 7
R/W
12
Input Voltage,
bit 6
R/W
11
Input Voltage,
bit 5
R/W
10
Input Voltage,
bit 4
R/W
9
Input Voltage,
bit 3
R/W
8
Input Voltage,
bit 2
R/W
6
Input Voltage,
bit 0
R/W
5
4
3
2
1
0
Reserved
R/W
7
Input Voltage,
bit 1
R/W
Reserved
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 35. InputVoltage Register (SMBus address = 3Dh) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
Reserved
R/W
00b
Not used. 1 = invalid write.
13
Input Voltage, bit 7
R/W
0b
0 = Adds 0 mV of input voltage.
12
Input Voltage, bit 6
R/W
0b
11
Input Voltage, bit 5
R/W
0b
10
Input Voltage, bit 4
R/W
0b
9
Input Voltage, bit 3
R/W
0b
8
Input Voltage, bit 2
R/W
0b
15-14
1 = Adds 8192 mV of input voltage.
0 = Adds 0 mV of input voltage.
1 = Adds 4096mV of input voltage.
0 = Adds 0 mV of input voltage.
1 = Adds 2048 mV of input voltage.
0 = Adds 0 mV of input voltage.
1 = Adds 1024 mV of input voltage.
0 = Adds 0 mV of input voltage.
1 = Adds 512 mV of input voltage.
0 = Adds 0 mV of input voltage.
1 = Adds 256 mV of input voltage.
Table 36. InputVoltage Register (SMBus address = 3Dh) Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION
7
Input Voltage, bit 1
R/W
0b
0 = Adds 0 mV of input voltage.
6
Input Voltage, bit 0
R/W
0b
Reserved
R/W
000000b
1 = Adds 128 mV of input voltage.
0 = Adds 0 mV of input voltage.
1 = Adds 64 mV of input voltage
5-0
54
Not used. Value Ignored.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.7 ADCVBUS/PSYS Register (SMBus address = 23h)
• PSYS: Full range: 3.06 V, LSB: 12 mV
• VBUS: Full range: 3200 mV to 19520 mV, LSB: 64 mV
Figure 28. ADCVBUS/PSYS Register (SMBus address = 23h)
15
14
13
12
11
10
9
8
R
R
R
R
R
R
R
R
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 37. ADCVBUS/PSYS Register Field Descriptions
BIT
FIELD
TYPE
RESET
DESCRIPTION
15-8
R
8-bit Digital Output of Input Voltage
7-0
R
8-bit Digital Output of System Power
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
55
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.8 ADCIBAT Register (SMBus address = 24h)
• ICHG: Full range: 8.128 A, LSB 64: mA
• IDCHG: Full range: 32.512 A, LSB: 256 mA
Figure 29. ADCIBAT Register (SMBus address = 24h)
15
14
13
12
11
10
9
8
Reserved
R
R
R
R
R
R
R
7
6
5
4
3
2
1
0
Reserved
R
R
R
R
R
R
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 38. ADCIBAT Register Field Descriptions
BIT
FIELD
TYPE
15
Reserved
R
Not used. Value ignored.
R
7-bit Digital Output of Battery Charge Current
R
Not used. Value ignored.
R
7-bit Digital Output of Battery Discharge Current
14-8
7
Reserved
6-0
56
RESET
DESCRIPTION
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.9 ADCIINCMPIN Register (SMBus address = 25h)
• IIN: Full range: 12.75 A, LSB: 50 mA
• CMPIN: Full range: 3.06 V, LSB: 12 mV
Figure 30. ADCIINCMPIN Register (SMBus address = 25h)
15
14
13
12
11
10
9
8
R
R
R
R
R
R
R
R
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 39. ADCIINCMPIN Register Field Descriptions
BIT
FIELD
TYPE
RESET
DESCRIPTION
15-8
R
8-bit Digital Output of Input Current
7-0
R
8-bit Digital Output of CMPIN voltage
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
57
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
8.6.10 ADCVSYSVBAT Register (SMBus address = 26h) (reset = )
• VSYS: Full range: 2.88 V to 19.2 V, LSB: 64 mV
• VBAT: Full range: 2.88 V to 19.2 V, LSB: 64 mV
Figure 31. ADCVSYSVBAT Register (SMBus address = 26h) (reset = )
15
14
13
12
11
10
9
8
R
R
R
R
R
R
R
R
7
6
5
4
3
2
1
0
R
R
R
R
R
R
R
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 40. ADCVSYSVBAT Register Field Descriptions
BIT
58
FIELD
TYPE
RESET
DESCRIPTION
15-8
R
8-bit Digital Output of System Voltage
7-0
R
8-bit Digital Output of Battery Voltage
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
8.6.11 ID Registers
8.6.11.1 ManufactureID Register (SMBus address = FEh) [reset = 0040h]
Figure 32. ManufactureID Register (SMBus address = FEh) [reset = 0040h]
15-0
MANUFACTURE_ID
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 41. ManufactureID Register Field Descriptions
SMBus
BIT
15-0
FIELD
TYPE
MANUFACTURE_ID
R
RESET
DESCRIPTION (READ ONLY)
40h
8.6.11.2 Device ID (DeviceAddress) Register (SMBus address = FFh) [reset = 0h]
Figure 33. Device ID (DeviceAddress) Register (SMBus address = FFh) [reset = 0h]
15-8
Reserved
R
7-0
DEVICE_ID
R
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 42. Device ID (DeviceAddress) Register Field Descriptions
SMBus
BIT
FIELD
TYPE
RESET
DESCRIPTION (READ ONLY)
15-8
Reserved
R
0b
Reserved
7-0
DEVICE_ID
R
0b
SMBus: 7Ch
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
59
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The bq2570xEVM-732 evaluation module (EVM) is a complete charger module for evaluating the bq25708. The
application curves were taken using the bq2570xEVM-732. Refer to the EVM user's guide (SLUUBG6) for EVM
information.
9.2 Typical Application
VSYS
6x10PF
2.2uH
RAC=10m:
RSR=10m:
ADAPTER
:
6x10PF
10nF
1PF
Optional
snubber
10:
Q1
Q2
Q3
47nF
10:
BATT
Q4
47nF
1:
15nF
15nF
HIDRV1
SW1 BTST1 BTST2 SW2
HIDRV2
LODRV2
VBUS LODRV1
SYS
470nF
/BATDRV
ACN
SRP
ACP
10:
REGN
SRN
REGN
VDDA
ILIM_HIZ
1uF
2.2±3.3uF
GND
bq25708
VDDA
350k:
CELL_BATPRESZ
250k:
COMP1
COMP2
IADPT
IBAT
PSYS
CHRG_OK
50:
/PROCHOT SDA SCL
1.05V
30k:
100pF
100pF
100k:
CMPOUT
CMPIN
10k:
To CPU
10k:
3.3V or 1.8V
10k:
10k:
Host
(SMBus)
Copyright © 2017, Texas Instruments Incorporated
Figure 34. Application Diagram
9.2.1 Design Requirements
DESIGN PARAMETER
Input Voltage
Input Current Limit
(1)
(2)
60
EXAMPLE VALUE
(1)
3.5V < Adapter Voltage < 24V
(1)
3.2A for 65W adapter
Battery Charge Voltage (2)
8400mV for 2s battery
Battery Charge Current (2)
3072mA for 2s battery
Refer to adapter specification for settings for Input Voltage and Input Current Limit.
Refer to battery specification for settings.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
Typical Application (continued)
DESIGN PARAMETER
EXAMPLE VALUE
Minimum System Voltage (2)
6144mV for 2s battery
9.2.2 Detailed Design Procedure
The parameters are configurable using the evaluation software. The simplified application circuit (see Figure 39,
as the application diagram) shows the minimum component requirements. Inductor, capacitor, and MOSFET
selection are explained in the rest of this section. Refer to the EVM user's guide (SLUUBG6) for the complete
application schematic.
9.2.2.1 ACP-ACN Input Filter
The bq25708 has average current mode control. The input current sensing through ACP/ACN is critical to
recover inductor current ripple. Parasitic inductance on board will generate high frequency ringing on ACP-ACN
which overwhelms converter sensed inductor current information, so it is difficult to manage parasitic inductance
created based on different PCB layout. Bigger parasitic inductance will generate bigger sense current ringing
which will cause the average current control loop to go into oscillation.
For real system board condition, we suggest to use below circuit design to get best result and filter noise induced
from different PCB parasitic factor. With time constant of filter from 47nsec to 200nsec, the filtering on ringing is
effective and in the meantime, the delay of on the sensed signal is small and therefore poses no concern for
average current mode control.
RAC
4~6x10uF
(0805)
Q1
1nF+10nF
(0402)
RACN
10 :
RACP
10 :
CDIFF
Open
CACP
15nF
ACP
CACN
15nF
ACN
HIDRV1
bq25708
Copyright © 2017, Texas Instruments Incorporated
Figure 35. ACN-ACP Input Filter
9.2.2.2 Inductor Selection
The bq25708 has two selectable fixed switching frequency. Higher switching frequency allows the use of smaller
inductor and capacitor values. Inductor saturation current should be higher than the charging current (ICHG) plus
half the ripple current (IRIPPLE):
ISAT ³ ICHG + (1/2) IRIPPLE
(3)
The inductor ripple current in buck operation depends on input voltage (VIN), duty cycle (DBUCK = VOUT/VIN),
switching frequency (fS) and inductance (L):
V ´ D ´ (1 - D)
IRIPPLE_BUCK = IN
fS ´ L
(4)
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
61
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
During boost operation, the duty cycle is:
DBOOST = 1 – (VBAT/VIN)
and the ripple current is:
IRIPPLE_BOOST = DBOOST x fS x VBAT/LBOOST
The maximum inductor ripple current happens with D = 0.5 or close to 0.5. For example, the battery charging
voltage range is from 9 V to 12.6 V for 3-cell battery pack. For 20 V adapter voltage, 10 V battery voltage gives
the maximum inductor ripple current. Another example is 4-cell battery, the battery voltage range is from 12 V to
16.8 V, and 12 V battery voltage gives the maximum inductor ripple current.
Usually inductor ripple is designed in the range of (20-40%) maximum charging current as a trade-off between
inductor size and efficiency for a practical design.
9.2.2.3 Input Capacitor
Bulk input capacitors should be locate in front of input current sensing resistor. Do not recommend to put bulk
input capacitors between input sensing resistor and switching MOSFET. Input capacitor should have enough
ripple current rating to absorb input switching ripple current. The worst case RMS ripple current is half of the
charging current when duty cycle is 0.5 in buck mode. If the converter does not operate at 50% duty cycle, then
the worst case capacitor RMS current occurs where the duty cycle is closest to 50% and can be estimated by
Equation 5:
ICIN = ICHG ´
D × (1 - D)
(5)
Low ESR ceramic capacitor such as X7R or X5R is preferred for input decoupling capacitor and should be
placed to the drain of the high side MOSFET and source of the low side MOSFET as close as possible. Voltage
rating of the capacitor must be higher than normal input voltage level. 25 V rating or higher capacitor is preferred
for 19-20 V input voltage. Minimum 10uF effective capacitance (7 pcs of 10uF 0805 size capacitor) is suggested
for 45 W-65 W adapter.
Ceramic capacitors show a dc-bias effect. This effect reduces the effective capacitance when a dc-bias voltage is
applied across a ceramic capacitor, as on the input capacitor of a charger. The effect may lead to a significant
capacitance drop, especially for high input voltages and small capacitor packages. See the manufacturer's
datasheet about the performance with a dc bias voltage applied. It may be necessary to choose a higher voltage
rating or nominal capacitance value in order to get the required value at the operating point.
9.2.2.4 Output Capacitor
Output capacitor also should have enough ripple current rating to absorb output switching ripple current. In buck
mode the output capacitor RMS current is given:
To get good loop stability, the resonant frequency of the output inductor and output capacitor should be designed
between 10 kHz and 20 kHz. The preferred ceramic capacitor is 25V X7R or X5R for output capacitor. Minimum
10uF effective capacitance (7 pcs of 10uF 0805 size capacitor) is suggested to be placed after the Q4 drain, and
50uF effective distributed capacitance on Vsys output. Place minimum 10uF after the charge current sense
resistor for best stability.
Ceramic capacitors show a dc-bias effect. This effect reduces the effective capacitance when a dc-bias voltage is
applied across a ceramic capacitor, as on the output capacitor of a charger. The effect may lead to a significant
capacitance drop, especially for high output voltages and small capacitor packages. See the manufacturer's data
sheet about the performance with a dc bias voltage applied. It may be necessary to choose a higher voltage
rating or nominal capacitance value in order to get the required value at the operating point.
9.2.2.5 Power MOSFETs Selection
Four external N-channel MOSFETs are used for a synchronous switching battery charger. The gate drivers are
internally integrated into the IC with 6V of gate drive voltage. 30 V or higher voltage rating MOSFETs are
preferred for 19-20 V input voltage.
Figure-of-merit (FOM) is usually used for selecting proper MOSFET based on a tradeoff between the conduction
loss and switching loss. For the top side MOSFET, FOM is defined as the product of a MOSFET's on-resistance,
RDS(ON), and the gate-to-drain charge, QGD. For the bottom side MOSFET, FOM is defined as the product of the
MOSFET's on-resistance, RDS(ON), and the total gate charge, QG.
FOMtop = RDS(on) x QGD; FOMbottom = RDS(on) x QG
62
Submit Documentation Feedback
(6)
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
The lower the FOM value, the lower the total power loss. Usually lower RDS(ON) has higher cost with the same
package size.
The top-side MOSFET loss includes conduction loss and switching loss. It is a function of duty cycle
(D=VOUT/VIN), charging current (ICHG), MOSFET's on-resistance (RDS(ON)), input voltage (VIN), switching frequency
(fS), turn on time (ton) and turn off time (toff):
1
Ptop = D ´ ICHG2 ´ RDS(on) +
´ VIN ´ ICHG ´ (t on + t off ) ´ f s
2
(7)
The first item represents the conduction loss. Usually MOSFET RDS(ON) increases by 50% with 100°C junction
temperature rise. The second term represents the switching loss. The MOSFET turn-on and turn-off times are
given by:
Q
Q
t on = SW , t off = SW
Ion
Ioff
(8)
where Qsw is the switching charge, Ion is the turn-on gate driving current and Ioff is the turn-off gate driving
current. If the switching charge is not given in MOSFET datasheet, it can be estimated by gate-to-drain charge
(QGD) and gate-to-source charge (QGS):
1
QSW = QGD +
´ QGS
2
(9)
Gate driving current can be estimated by REGN voltage (VREGN), MOSFET plateau voltage (Vplt), total turn-on
gate resistance (Ron) and turn-off gate resistance (Roff) of the gate driver:
VREGN - Vplt
Vplt
Ion =
, Ioff =
Ron
Roff
(10)
The conduction loss of the bottom-side MOSFET is calculated with the following equation when it operates in
synchronous continuous conduction mode:
Pbottom = (1 - D) x ICHG 2 x RDS(on)
(11)
When charger operates in non-synchronous mode, the bottom-side MOSFET is off. As a result all the
freewheeling current goes through the body-diode of the bottom-side MOSFET. The body diode power loss
depends on its forward voltage drop (VF), non-synchronous mode charging current (INONSYNC), and duty cycle (D).
PD = VF x INONSYNC x (1 - D)
(12)
The maximum charging current in non-synchronous mode can be up to 0.25 A for a 10 mΩ charging current
sensing resistor or 0.5 A if battery voltage is below 2.5 V. The minimum duty cycle happens at lowest battery
voltage. Choose the bottom-side MOSFET with either an internal Schottky or body diode capable of carrying the
maximum non-synchronous mode charging current.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
63
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
9.2.3 Application Curves
CH1: VBUS
CH1: VBUS
CH2: VDDA
CH2: VDDA
CH3: CHRG_OK
CH3: CHRG_OK
CH4: VSYS
CH4: VSYS
2-cell without battery
2-cell without battery
Figure 36. Power Up from 20 V
Figure 37. Power Up from 5 V
CH1: VBUS
CH1: VBUS
CH2: SW1
CH2: SW1
CH3: SW2
CH3: SW2
CH4: VSYS with 9Vos
CH4: IL
3-cell VBAT = 10 V
VBUS 5 V to 20 V
Figure 38. Power Off from 12 V
CH2: SW1
Figure 39. System Regulation
CH1: HIDRV1
CH2: SW1
CH3: LODRV1
CH3: SW2
CH1: IL
CH4: IL
VBUS = 20 V, VSYS = 10 V, ISYS = 200 mA
Figure 40. PFM Operation
64
Figure 41. PWM Operation
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
CH2: SW2
CH2: SW1
CH1: HIDRV2
CH3: SW2
CH3: LODRV2
CH4: IL
CH4: IL
VBUS = 5 V, VBAT = 10 V
VBUS = 12 V, VBAT = 12 V
Figure 42. Switching During Boost Mode
Figure 43. Switching During Buck Boost Mode
CH1: VSYS
CH1: VSYS
CH2: IIN
CH2: IIN
CH3: ISYS
CH3: ISYS
VBUS = 12 V/3.3 A, 3-cell, VSYS = 9 V, Without battery
Figure 44. System Regulation in Buck Mode
CH1: VSYS
VBUS = 9 V/3.3 A, 3-cell, VSYS = 9 V, Without battery
Figure 45. System Regulation in Buck Boost Mode
CH2: IIN
CH2: IIN
CH3: ISYS
CH4: IBAT
CH3: ISYS
VBUS = 5 V/3.3 A, 3-cell, VSYS = 9 V, Without battery
Figure 46. System Regulation in Boost Mode
VBUS = 20 V/3.3 V, VBAT = 7.5 V
Figure 47. Input Current Regulation in Buck Mode
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
65
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
CH2:IIN
CH3:ISYS
CH4:IBAT
VBUS = 5 V/3.3 V, VBAT = 7.5 V
Figure 48. Input Current in Boost Mode
10 Power Supply Recommendations
The valid adapter range is from 3.5V (VBUS_UVLOZ) to 24V (ACOV) with at least 500mA current rating. When
CHRG_OK goes HIGH, the system is powered from adapter through the charger. When adapter is removed, the
system is connected to battery through BATFET. Typically the battery depletion threshold should be greater than
the minimum system voltage so that the battery capacity can be fully utilized for maximum battery life.
66
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
11 Layout
11.1 Layout Guidelines
The switching node rise and fall times should be minimized for minimum switching loss. Proper layout of the
components to minimize high frequency current path loop (see Layout Example section) is important to prevent
electrical and magnetic field radiation and high frequency resonant problems. Here is a PCB layout priority list for
proper layout. Layout PCB according to this specific order is essential.
1. Place the input capacitor as close as possible to the supply of the switching MOSFET and ground
connections. Use a short copper trace connection. These parts must be placed on the same layer of PCB
using vias to make this connection.
2. The device must be placed close to the gate pins of the switching MOSFET. Keep the gate drive signal
traces short for a clean MOSFET drive. The device can be placed on the other side of the PCB of switching
MOSFETs.
3. Place an inductor input pin as close as possible to the output pin of the switching MOSFET. Minimize the
copper area of this trace to lower electrical and magnetic field radiation but make the trace wide enough to
carry the charging current. Do not use multiple layers in parallel for this connection. Minimize parasitic
capacitance from this area to any other trace or plane.
4. The charging current sensing resistor should be placed right next to the inductor output. Route the sense
leads connected across the sensing resistor back to the device in same layer, close to each other (minimize
loop area) and do not route the sense leads through a high-current path (see Figure 50 for Kelvin connection
for best current accuracy). Place a decoupling capacitor on these traces next to the device.
5. Place an output capacitor next to the sensing resistor output and ground.
6. Output capacitor ground connections must be tied to the same copper that connects to the input capacitor
ground before connecting to system ground.
7. Use a single ground connection to tie the charger power ground to the charger analog ground. Just beneath
the device, use analog ground copper pour but avoid power pins to reduce inductive and capacitive noise
coupling.
8. Route analog ground separately from power ground. Connect analog ground and connect power ground
separately. Connect analog ground and power ground together using power pad as the single ground
connection point. Or using a 0-Ω resistor to tie analog ground to power ground (power pad should tie to
analog ground in this case if possible).
9. Decoupling capacitors must be placed next to the device pins. Make trace connection as short as possible.
10. It is critical that the exposed power pad on the backside of the device package be soldered to the PCB
ground.
11. The via size and number should be enough for a given current path. See the EVM design (SLUUBG6) for
the recommended component placement with trace and via locations. For the WQFN information, see
SLUA271.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
67
bq25708
SLUSCU2 – NOVEMBER 2017
www.ti.com
11.2 Layout Example
11.2.1 Layout Consideration of Current Path
L1
PHASE
VIN
C1
High
Frequency
Current
Path
R1
VBAT
BAT
GND
C2
Figure 49. High Frequency Current Path
11.2.2 Layout Consideration of Short Circuit Protection
Charge Current Direction
R SNS
To Inductor
To Capacitor and battery
Current Sensing Direction
To SRP and SRN pin
Figure 50. Sensing Resistor PCB Layout
68
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
bq25708
www.ti.com
SLUSCU2 – NOVEMBER 2017
12 Device and Documentation Support
12.1 Device Support
12.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
12.2 Documentation Support
12.2.1 Related Documentation
For related documentation see the following:
• Semiconductor and IC Package Thermal Metrics Application Report (SPRA953)
• bq25700 Evaluation Module User's Guide (SLUUBG6)
• QFN/SON PCB Attachment Application Report (SLUA271)
12.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.5 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
Submit Documentation Feedback
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: bq25708
69
PACKAGE OPTION ADDENDUM
www.ti.com
12-Dec-2017
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
BQ25708RSNR
ACTIVE
QFN
RSN
32
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
BQ25708
BQ25708RSNT
ACTIVE
QFN
RSN
32
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
BQ25708
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
12-Dec-2017
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
9-Dec-2017
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
BQ25708RSNR
QFN
RSN
32
3000
330.0
12.4
4.25
4.25
1.15
8.0
12.0
Q2
BQ25708RSNT
QFN
RSN
32
250
180.0
12.4
4.25
4.25
1.15
8.0
12.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
9-Dec-2017
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
BQ25708RSNR
QFN
RSN
32
3000
367.0
367.0
35.0
BQ25708RSNT
QFN
RSN
32
250
210.0
185.0
35.0
Pack Materials-Page 2
IMPORTANT NOTICE
Texas Instruments Incorporated (TI) reserves the right to make corrections, enhancements, improvements and other changes to its
semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers
should obtain the latest relevant information before placing orders and should verify that such information is current and complete.
TI’s published terms of sale for semiconductor products (http://www.ti.com/sc/docs/stdterms.htm) apply to the sale of packaged integrated
circuit products that TI has qualified and released to market. Additional terms may apply to the use or sale of other types of TI products and
services.
Reproduction of significant portions of TI information in TI data sheets is permissible only if reproduction is without alteration and is
accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such reproduced
documentation. Information of third parties may be subject to additional restrictions. Resale of TI products or services with statements
different from or beyond the parameters stated by TI for that product or service voids all express and any implied warranties for the
associated TI product or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements.
Buyers and others who are developing systems that incorporate TI products (collectively, “Designers”) understand and agree that Designers
remain responsible for using their independent analysis, evaluation and judgment in designing their applications and that Designers have
full and exclusive responsibility to assure the safety of Designers' applications and compliance of their applications (and of all TI products
used in or for Designers’ applications) with all applicable regulations, laws and other applicable requirements. Designer represents that, with
respect to their applications, Designer has all the necessary expertise to create and implement safeguards that (1) anticipate dangerous
consequences of failures, (2) monitor failures and their consequences, and (3) lessen the likelihood of failures that might cause harm and
take appropriate actions. Designer agrees that prior to using or distributing any applications that include TI products, Designer will
thoroughly test such applications and the functionality of such TI products as used in such applications.
TI’s provision of technical, application or other design advice, quality characterization, reliability data or other services or information,
including, but not limited to, reference designs and materials relating to evaluation modules, (collectively, “TI Resources”) are intended to
assist designers who are developing applications that incorporate TI products; by downloading, accessing or using TI Resources in any
way, Designer (individually or, if Designer is acting on behalf of a company, Designer’s company) agrees to use any particular TI Resource
solely for this purpose and subject to the terms of this Notice.
TI’s provision of TI Resources does not expand or otherwise alter TI’s applicable published warranties or warranty disclaimers for TI
products, and no additional obligations or liabilities arise from TI providing such TI Resources. TI reserves the right to make corrections,
enhancements, improvements and other changes to its TI Resources. TI has not conducted any testing other than that specifically
described in the published documentation for a particular TI Resource.
Designer is authorized to use, copy and modify any individual TI Resource only in connection with the development of applications that
include the TI product(s) identified in such TI Resource. NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE
TO ANY OTHER TI INTELLECTUAL PROPERTY RIGHT, AND NO LICENSE TO ANY TECHNOLOGY OR INTELLECTUAL PROPERTY
RIGHT OF TI OR ANY THIRD PARTY IS GRANTED HEREIN, including but not limited to any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
regarding or referencing third-party products or services does not constitute a license to use such products or services, or a warranty or
endorsement thereof. Use of TI Resources may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
TI RESOURCES ARE PROVIDED “AS IS” AND WITH ALL FAULTS. TI DISCLAIMS ALL OTHER WARRANTIES OR
REPRESENTATIONS, EXPRESS OR IMPLIED, REGARDING RESOURCES OR USE THEREOF, INCLUDING BUT NOT LIMITED TO
ACCURACY OR COMPLETENESS, TITLE, ANY EPIDEMIC FAILURE WARRANTY AND ANY IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF ANY THIRD PARTY INTELLECTUAL
PROPERTY RIGHTS. TI SHALL NOT BE LIABLE FOR AND SHALL NOT DEFEND OR INDEMNIFY DESIGNER AGAINST ANY CLAIM,
INCLUDING BUT NOT LIMITED TO ANY INFRINGEMENT CLAIM THAT RELATES TO OR IS BASED ON ANY COMBINATION OF
PRODUCTS EVEN IF DESCRIBED IN TI RESOURCES OR OTHERWISE. IN NO EVENT SHALL TI BE LIABLE FOR ANY ACTUAL,
DIRECT, SPECIAL, COLLATERAL, INDIRECT, PUNITIVE, INCIDENTAL, CONSEQUENTIAL OR EXEMPLARY DAMAGES IN
CONNECTION WITH OR ARISING OUT OF TI RESOURCES OR USE THEREOF, AND REGARDLESS OF WHETHER TI HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
Unless TI has explicitly designated an individual product as meeting the requirements of a particular industry standard (e.g., ISO/TS 16949
and ISO 26262), TI is not responsible for any failure to meet such industry standard requirements.
Where TI specifically promotes products as facilitating functional safety or as compliant with industry functional safety standards, such
products are intended to help enable customers to design and create their own applications that meet applicable functional safety standards
and requirements. Using products in an application does not by itself establish any safety features in the application. Designers must
ensure compliance with safety-related requirements and standards applicable to their applications. Designer may not use any TI products in
life-critical medical equipment unless authorized officers of the parties have executed a special contract specifically governing such use.
Life-critical medical equipment is medical equipment where failure of such equipment would cause serious bodily injury or death (e.g., life
support, pacemakers, defibrillators, heart pumps, neurostimulators, and implantables). Such equipment includes, without limitation, all
medical devices identified by the U.S. Food and Drug Administration as Class III devices and equivalent classifications outside the U.S.
TI may expressly designate certain products as completing a particular qualification (e.g., Q100, Military Grade, or Enhanced Product).
Designers agree that it has the necessary expertise to select the product with the appropriate qualification designation for their applications
and that proper product selection is at Designers’ own risk. Designers are solely responsible for compliance with all legal and regulatory
requirements in connection with such selection.
Designer will fully indemnify TI and its representatives against any damages, costs, losses, and/or liabilities arising out of Designer’s noncompliance with the terms and provisions of this Notice.
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2017, Texas Instruments Incorporated