DATASHEET

SMBus Level 2 Battery Charger
ISL88731C
Features
The ISL88731C is a highly integrated Lithium-ion battery
charger controller, programmable over the SMBus system
management bus (SMBus). The ISL88731C is intended to be
used in a smart battery charger (SBC) within a smart battery
system (SBS) that throttles the charge power such that the
current from the AC-adapter is automatically limited. High
efficiency is achieved with a DC/DC synchronous-rectifier buck
converter, equipped with diode emulation for enhanced light
load efficiency and system bus boosting prevention. The
ISL88731C charges one to four Lithium-ion series cells, and
delivers up to 8A charge current. Integrated MOSFET drivers
and bootstrap diode result in fewer components and smaller
implementation area. Low offset current-sense amplifiers
provide high accuracy with 10mΩ sense resistors. The
ISL88731C provides 0.5% end-of-charge battery voltage
accuracy.
• 0.5% Battery Voltage Accuracy
• 3% Adapter Current Limit Accuracy
• 3% Charge Current Accuracy
• SMBus 2-Wire Serial Interface
• Battery Short Circuit Protection
• Fast Response for Pulse-Charging
• Fast System-Load Transient Response
• Monitor Outputs
- Adapter Current (3% Accuracy)
- AC-Adapter Detection
• 11-Bit Battery Voltage Setting
• 6 Bit Charge Current/Adapter Current Setting
The ISL88731C provides a digital output that indicates the
presence of the AC adapter as well as an analog output which
indicates the adapter current within 4% accuracy.
• 8A Maximum Battery Charger Current
• 11A Maximum Adapter Current
• +8V to +26V Adapter Voltage Range
The ISL88731C is available in a small 5mmx5mm 28 Ld Thin
(0.8mm) QFN package. An evaluation kit is available to reduce
design time. The ISL88731C is available in Pb-Free packages.
• Pb-Free (RoHS Compliant)
Related Literature
• Notebook Computers
• Tablet PCs
• See AN1404 for “ISL88731EVAL2Z and ISL88731CEVAL2Z
Evaluation Boards Setup Procedure”
100
3.0
VCHG (V)
2.0
11.5
1.5
11.0
1.0
10.5
20
40
60
16.8V BATTERY
90
12.6V BATTERY
8.4V BATTERY
85
4.2V BATTERY
80
100
120
140
0.0
160
FIGURE 1. TYPICAL CHARGING VOLTAGE AND CURRENT
1
80
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
IOUT (A)
CHARGE TIME (MINUTES)
June 8, 2011
FN6978.3
95
0.5
ICHG (A)
0
BATTERY CURRENT
2.5
12.0
EFFICIENCY (%)
12.5
BATTERY VOLTAGE
• Portable Equipment with Rechargeable Batteries
3.5
13.0
10.0
Applications
FIGURE 2. EFFICIENCY vs CHARGE CURRENT AND BATTERY
VOLTAGE
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas Inc. 2010, 2011. All Rights Reserved
Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
All other trademarks mentioned are the property of their respective owners.
ISL88731C
VCC
DCIN
VDDSMB
SDA
SMBUS
11
DACV
DACV
6
DACS
DACS
DACI
DACI
6
SCL
LINEAR
REGULATOR
REFERENCE
VDDP
3.2V
VREF
ACOK
+
-
EN
ACIN
ICM
BUFF
CSSP
CSSN
LEVEL
SHIFTER
20x
DACS
EN
GMS
+
BOOT
ICOMP
CSOP
CSON
CSO
LEVEL
SHIFTER
20x
DACI
UGATE
GMI
PHASE
DC/DC
CONVERTER
+
LVB
+
DACV
VDDP
LVB
GMV
LGATE
VFB
500k
100k
PGND
EN
CSSP
GND
VCOMP
FIGURE 3. FUNCTIONAL BLOCK DIAGRAM
AC ADAPTER
TO SYSTEM
RS1
CSSP
ACIN
DCIN
CSSN
UGATE
PHASE
RS2
TO BATTERY
ISL88731C
BOOT
LGATE
ICOMP
VCOMP
VDDP
VREF
VCC
CSOP
CSON
VFB
PGND
ACOK
ICM
SDA
SCL
VDDSMB
PGND
HOST
AGND
GND
AGND
FIGURE 4. TYPICAL APPLICATION CIRCUIT
2
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June 8, 2011
ISL88731C
Pin Configuration
CSSP
CSSN
VCC
BOOT
UGATE
PHASE
DCIN
ISL88731C
(28 LD TQFN)
TOP VIEW
28
27
26
25
24
23
22
NC
1
21
VDDP
ACIN
2
20
LGATE
VREF
3
19
PGND
ICOMP
4
18
CSOP
NC
5
17
CSON
VCOMP
6
16
NC
NC
7
15
VFB
8
9
10
11
12
13
14
ICM
SDA
SCL
VDDSMB
GND
ACOK
NC
PD
Functional Pin Descriptions
PIN NUMBER
SYMBOL
DESCRIPTION
2
ACIN
AC Adapter Detection Input. Connect to a resistor divider from the AC adapter output. Range zero to 5.5V.
3
VREF
Reference Voltage output. Range 3.168V to 3.232V. It is internally compensated. Do not connect a decoupling capacitor.
4
ICOMP
Compensation Point for the charging current and adapter current regulation Loop. Connect 0.01µF to GND. See
“Voltage Control Loop” on page 21 for details on selecting the ICOMP capacitor. Range zero to 5.5V.
6
VCOMP
Compensation Point for the voltage regulation loop. Connect 4.7kΩ in series with 0.01µF to GND. See “Voltage Control
Loop” on page 21 for details on selecting VCOMP components. Range zero to 5.5V.
8
ICM
Input Current Monitor Output. ICM voltage equals 20 x (VCSSP - VCSSN). Range zero to 3V.
9
SDA
SMBus Data I/O. Open-drain Output. Connect an external pull-up resistor according to SMBus specifications. Range
zero to 5.5V.
10
SCL
SMBus Clock Input. Connect an external pull-up resistor according to SMBus specifications. Range zero to 5.5V.
11
VDDSMB
12
GND
Analog Ground. Connect directly to the backside paddle. Connect to the backside paddle and PGND at one point close
to (under) the IC.
13
ACOK
AC Detect Output. This open drain output is high impedance when ACIN is greater than 3.2V. The ACOK output remains low
when the ISL88731C is powered down. Connect a 10k pull-up resistor from ACOK to VDDSMB. Range 3.3V to 5.5V.
15
VFB
17
CSON
Charge Current-Sense Negative Input. Range 1V to 19V.
18
CSOP
Charge Current-Sense Positive Input. Range 1V to 19V.
19
PGND
Power Ground. Connect PGND to the source of the low side MOSFET and the negative side of capacitors to the charger output
and the drain of the upper switching FET. Connect this area to the Backside paddle at one location very near (under) the IC.
20
LGATE
Low-Side Power MOSFET Driver Output. Connect to low-side N channel MOSFET. LGATE drives between VDDP and
PGND. Range is -0.3V to 5.23V.
SMBus interface Supply Voltage Input. Bypass with a 0.1µF capacitor to GND. Range 3.3V to 5.5V.
Feedback for the Battery Voltage. Range 1V to 19V.
3
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June 8, 2011
ISL88731C
Functional Pin Descriptions (Continued)
PIN NUMBER
SYMBOL
DESCRIPTION
21
VDDP
Linear Regulator Output. VDDP is the output of the 5.2V linear regulator supplied from DCIN. VDDP also directly
supplies the LGATE driver and the BOOT strap diode. Bypass with a 1µF ceramic capacitor from VDDP to PGND. Range
is 5.0V to 5.23V.
22
DCIN
Charger Bias Supply Input. Bypass DCIN with a 0.1µF capacitor to GND. Range 8V to +26V.
23
PHASE
High-Side Power MOSFET Driver Source Connection. Connect to the source of the high-side N-Channel MOSFET. Range
-2V to +26V.
24
UGATE
High-Side Power MOSFET Driver Output. Connect to the high-side N-channel MOSFET gate. Range -2V to +33V.
25
BOOT
High-Side Power MOSFET Driver Power-Supply Connection. Connect a 0.1µF capacitor from BOOT-to-PHASE. Range
-2V to +33V.
26
VCC
27
CSSN
Input Current-Sense Negative Input. Range 8V to 26V.
28
CSSP
Input Current-Sense Positive Input. Range 8V to 26V.
1, 5, 7, 14, 16
Power input for internal analog circuits. Connect a 4.7Ω resistor from VCC to VDDP and a 1µF ceramic capacitor from VCC
to ground. Range 4V to 5.23V.
PD
Connect the backside paddle to GND. This pad has the lowest thermal resistance to the die. It should be connected to
a large area of ground with 3 to 5 vias for good thermal performance. The recommended potential of the thermal pad
is zero (0) Volts.
NC
No Connect. Pins are not connected internally.
Ordering Information
PART NUMBER
(Notes 1, 2, 3)
PART
MARKING
ISL88731CHRTZ
88731C HRTZ
ISL88731CEVAL2Z
Evaluation Board
TEMP RANGE
(°C)
-10 to +100
PACKAGE
(Pb-Free)
28 Ld 5x5 TQFN
PKG.
DWG. #
L28.5x5B
NOTES:
1. Add “-T*” suffix for tape and reel. Please refer to TB347 for details on reel specifications.
2. These Intersil Pb-free plastic packaged products employ special Pb-free material sets, molding compounds/die attach materials, and 100% matte
tin plate plus anneal (e3 termination finish, which is RoHS compliant and compatible with both SnPb and Pb-free soldering operations). Intersil
Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.
3. For Moisture Sensitivity Level (MSL), please see device information page for ISL88731C. For more information on MSL please see tech brief TB363.
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FN6978.3
June 8, 2011
ISL88731C
Table of Contents
Absolute Maximum Ratings ...................................................6
Writing to the Internal Registers .........................................17
Thermal Information ...............................................................6
Reading from the Internal Registers...................................17
Electrical Specifications ........................................................6
Application Information .......................................................17
SMBus Timing Specifications.................................................8
Inductor Selection ....................................................................... 17
Output Capacitor Selection ........................................................ 18
MOSFET Selection ....................................................................... 18
Snubber Design ........................................................................... 19
Input Capacitor Selection........................................................... 19
Loop Compensation Design....................................................... 19
Transconductance Amplifiers GMV, GMI and GMS ................ 19
PWM Gain Fm .............................................................................. 19
Charge Current Control Loop ..................................................... 20
Adapter Current Limit Control Loop.......................................... 20
Voltage Control Loop................................................................... 21
Output LC Filter Transfer Functions .......................................... 21
Compensation Break Frequency Equations ............................ 22
Typical Operating Performance ...................................................9
Theory of Operation ............................................................. 11
Introduction ..................................................................................11
PWM Control.................................................................................11
AC-Adapter Detection..................................................................11
Current Measurement.................................................................11
VDDP Regulator ...........................................................................11
VDDSMB Supply ...........................................................................11
Short Circuit Protection and 0V Battery Charging ..................11
Undervoltage Detect and Battery Trickle Charging ................11
Over-Temperature Protection ....................................................12
Overvoltage Protection ...............................................................12
The System Management Bus...................................................12
General SMBus Architecture......................................................12
Data Validity .................................................................................12
START and STOP Conditions..............................................................12
Acknowledge.........................................................................................13
SMBus Transactions............................................................................13
PCB Layout Considerations................................................. 22
Setting Charge Voltage........................................................ 14
Power and Signal Layers Placement on the PCB ................... 22
Component Placement............................................................... 22
Signal Ground and Power Ground Connection........................ 22
GND and VCC Pin......................................................................... 22
LGATE Pin ..................................................................................... 22
PGND Pin ...................................................................................... 22
PHASE Pin .................................................................................... 23
UGATE Pin..................................................................................... 23
BOOT Pin....................................................................................... 23
CSOP, CSON, CSSP and CSSN Pins .......................................... 23
DCIN Pin........................................................................................ 23
Copper Size for the Phase Node ............................................... 23
Identify the Power and Signal Ground ..................................... 23
Clamping Capacitor for Switching MOSFET............................. 23
Setting Charge Current ........................................................ 15
Revision History ................................................................... 24
Setting Input-Current Limit.................................................. 16
Products................................................................................ 24
Charger Timeout ....................................................................17
Package Outline Drawing .................................................... 25
Byte Format .......................................................................... 13
ISL88731C and SMBus ......................................................... 13
Battery Charger Registers................................................... 14
Enabling and Disabling Charging........................................ 14
ISL88731C Data Byte Order..................................................17
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June 8, 2011
ISL88731C
Absolute Maximum Ratings
Thermal Information
DCIN, CSSP, CSSN, CSOP, CSON, VFB . . . . . . . . . . . . . . . . . . . -0.3V to +28V
CSSP-CSSN, CSOP-CSON, PGND-GND . . . . . . . . . . . . . . . . . . -0.3V to +0.3V
PHASE to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -6V to +30V
BOOT to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +33V
BOOT to PHASE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V
UGATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PHASE - 0.3V to BOOT + 0.3V
LGATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PGND - 0.3V to VDDP + 0.3V
ICOMP, VCOMP, VREF, to GND . . . . . . . . . . . . . . . . . . . . . -0.3V to VCC + 0.3V
VDDSMB, SCL, SDA, ACIN, ACOK . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V
VDDP, ICM, VCC to GND, VDDP to PGND . . . . . . . . . . . . . . . . . . -0.3V to +6V
Thermal Resistance (Typical)
θJA (°C/W) θJC (°C/W)
28 Ld TQFN Package (Notes 4, 5) . . . . . . .
38
6.5
Junction Temperature Range . . . . . . . . . . . . . . . . . . . . . . . -55°C to +150°C
Operating Temperature Range . . . . . . . . . . . . . . . . . . . . . . -10°C to +100°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65°C to +150°C
Pb-Free Reflow Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product
reliability and result in failures not covered by warranty.
NOTES:
4. θJA is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. See Tech
Brief TB379.
5. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside.
Electrical Specifications DCIN = CSSP = CSSN = 18V, CSOP = CSON = 12V, VDDP = 5V, BOOT-PHASE = 5.0V, GND = PGND = 0V,
CVDDP = 1µF, IVDDP = 0mA, TA = -10°C to +100°C. Boldface limits apply over the operating temperature range, -10°C to +100°C.
PARAMETER
CONDITIONS
MIN
(Note 7)
TYP
MAX
(Note 7)
UNITS
16.716
16.8
16.884
V
0.5
%
12.655
V
0.5
%
8.450
V
0.6
%
4.221
V
0.7
%
CHARGE VOLTAGE REGULATION
Battery Full Charge Voltage and Accuracy
ChargeVoltage = 0x41A0
-0.5
ChargeVoltage = 0x3130
12.529
12.592
-0.5
ChargeVoltage = 0x20D0
8.350
8.4
-0.6
ChargeVoltage = 0x1060
4.163
4.192
-0.7
Battery Undervoltage Lockout Trip Point for
Trickle Charge
VFB rising
2.55
2.7
2.85
V
100
250
400
mV
78.22
80.64
83.06
mV
RS2 = 10mΩ (see Figure 4)
ChargingCurrent = 0x1f80
7.822
8.064
8.306
A
3
%
RS2 = 10mΩ (see Figure 4)
ChargingCurrent = 0x0f80
3.809
RS2 = 10mΩ (see Figure 4)
ChargingCurrent = 0x0080
64
Based on charge current = 128mA and 8.064A
Battery Undervoltage Lockout Trip Point
Hysteresis
CHARGE CURRENT REGULATION
CSOP to CSON Full-Scale
Current-Sense Voltage
Charge Current and Accuracy
Charge Current Gain Error
CSOP/CSON Input Voltage Range
6
-3
3.968
4.126
A
4
%
220
mA
-1.6
1.4
%
0
19
V
-4
128
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June 8, 2011
ISL88731C
Electrical Specifications DCIN = CSSP = CSSN = 18V, CSOP = CSON = 12V, VDDP = 5V, BOOT-PHASE = 5.0V, GND = PGND = 0V,
CVDDP = 1µF, IVDDP = 0mA, TA = -10°C to +100°C. Boldface limits apply over the operating temperature range, -10°C to +100°C. (Continued)
PARAMETER
CONDITIONS
Battery Quiescent Current
MIN
(Note 7)
Adapter present, not charging,
ICSOP + ICSON + IPHASE + ICSSP + ICSSN + IFB
VPHASE = VCSON = VCSOP = VDCIN = 19V,
VACIN = 5V
Adapter Absent
ICSOP + ICSON + IPHASE + ICSSP + ICSSN + IFB
VPHASE = VCSON = VCSOP = 19V, VDCIN = 0V
Adapter Quiescent Current
-1
IDCIN + ICSSP + ICSSN
Vadapter = 8V to 26V, Vbattery 4V to 16.8V
TYP
MAX
(Note 7)
UNITS
135
200
µA
0.2
2
µA
3
5
mA
110
113.3
mV
INPUT CURRENT REGULATION
CSSP to CSSN Full-Scale Current-Sense
Voltage
CSSP = 19V
Input Current Accuracy
RS1 = 10mΩ (see Figure 4)
Adapter Current = 11004mA or 3584mA
-3
3
%
RS1 = 10mΩ (see Figure 4)
Adapter Current = 2048mA
-5
5
%
-1.5
1.5
%
Input Current Limit Offset
-1
1
mV
CSSP/CSSN Input Voltage Range
8
26
V
Input Current Limit Gain Error
Based on InputCurrent = 1024mA and 11004mA
ICM Gain
VCSSP-CSSN = 110mV
ICM Accuracy
VCSSP-CSSN = 110mV
ICM Max Output Current
106.7
20
V/V
-2.5
2.5
%
VCSSP-CSSN = 55mV or 35mV
-4
4
%
VCSSP-CSSN = 20mV
-8
8
%
500
µA
26
V
5.1
5.23
V
35
100
mV
5.5
V
VCSSP-CSSN = 0.1V
SUPPLY AND LINEAR REGULATOR
DCIN, Input Voltage Range
8
VDDP Output Voltage
8.0V < VDCIN < 28V, no load
VDDP Load Regulation
0 < IVDDP < 30mA
5.0
VDDSMB Range
2.7
VDDSMB UVLO Rising
2.4
2.5
2.6
V
VDDSMB UVLO Hysteresis
40
100
150
mV
20
27
µA
3.168
3.2
3.232
V
2
8
VDDSMB Quiescent Current
VDDP = SCL = SDA = 5.5V
V REFERENCE
VREF Output Voltage
0 < IVREF < 300µA
ACOK
ACOK Sink Current
VACOK = 0.4V, ACIN = 1.5V
ACOK Leakage Current
VACOK = 5.5V, ACIN = 3.7V
mA
1
µA
ACIN
ACIN rising Threshold
3.15
3.2
3.25
V
ACIN Threshold Hysteresis
40
60
90
mV
ACIN Input Bias Current
-1
1
µA
7
FN6978.3
June 8, 2011
ISL88731C
Electrical Specifications DCIN = CSSP = CSSN = 18V, CSOP = CSON = 12V, VDDP = 5V, BOOT-PHASE = 5.0V, GND = PGND = 0V,
CVDDP = 1µF, IVDDP = 0mA, TA = -10°C to +100°C. Boldface limits apply over the operating temperature range, -10°C to +100°C. (Continued)
PARAMETER
CONDITIONS
MIN
(Note 7)
TYP
MAX
(Note 7)
UNITS
330
400
440
kHz
170
290
400
µA
0
2
µA
SWITCHING REGULATOR
Frequency
BOOT Supply Current
UGATE High
PHASE Input Bias Current
VDCON = 28V, VCSON = VPHASE = 20V
UGATE On-Resistance Low
IUGATE = -100mA
0.9
1.6
Ω
UGATE On-Resistance High
IUGATE = 10mA
1.4
2.5
Ω
LGATE On-Resistance High
ILGATE = +10mA
1.4
2.5
Ω
LGATE On-Resistance Low
ILGATE = -100mA
0.9
1.6
Ω
Dead Time
Falling UGATE to rising LGATE or
falling LGATE to rising UGATE
35
50
80
ns
GMV Amplifier Transconductance
200
250
300
µA/V
GMI Amplifier Transconductance
40
50
60
µA/V
GMS Amplifier Transconductance
40
50
60
µA/V
GMI/GMS Saturation Current
15
21
25
µA
GMV Saturation Current
10
17
30
µA
200
300
400
mV
0.8
V
ERROR AMPLIFIERS
ICOMP, VCOMP Clamp Voltage
0.25V < VICOMP, VCOMP < 3.5V
LOGIC LEVELS
SDA/SCL Input Low Voltage
VDDSMB = 2.7V to 5.5V
SDA/SCL Input High Voltage
VDDSMB = 2.7V to 5.5V
2
SDA/SCL Input Bias Current
VDDSMB = 2.7V to 5.5V
-1
SDA, Output Sink Current
VSDA = 0.4V
7
SMBus Timing Specifications
V
1
15
µA
mA
VDDSMB = 2.7V to 5.5V.
PARAMETER
SMBus Frequency
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
100
kHz
FSMB
10
tBUF
4.7
µs
tHD:STA
4
µs
Start Condition Setup Time from SCL
tSU:STA
4.7
µs
Stop Condition Setup Time from SCL
tSU:STO
4
µs
SDA Hold Time from SCL
tHD:DAT
300
ns
SDA Setup Time from SCL
tSU:DAT
250
ns
SCL Low Timeout (Note 6)
Bus Free Time
Start Condition Hold Time from SCL
tTIMEOUT
22
SCL Low Period
tLOW
4.7
µs
SCL High Period
tHIGH
4
µs
Maximum Charging Period without an SMBus Write to
ChargeVoltage or ChargeCurrent Register
140
25
180
30
220
ms
s
NOTES:
6. If SCL is low for longer than the specified time, the charger is disabled.
7. Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature limits established by characterization
and are not production tested.
8
FN6978.3
June 8, 2011
ISL88731C
Typical Operating Performance
DCIN = 20V, 3S2P Li-Battery, TA = +25°C, unless otherwise noted.
5.15
3.23
5.10
3.22
5.05
3.21
1.0%
VREF (V)
VDDP (V)
0.5%
5.00
0.0%
3.20
4.95
3.19
4.90
3.18
-0.5%
4.85
0
20
40
60
80
VDDP LOAD CURRENT (mA)
3.17
0
100
100
I VREF (µA)
-1.0%
200
150
FIGURE 6. VREF LOAD REGULATION
FIGURE 5. VDD LOAD REGULATION
13.0
10
12.5
BATTERY VOLTAGE
15
5
0
-5
3.5
3.0
2.5
12.0
VCHG (V)
2.0
11.5
1.5
11.0
1.0
10.5
-10
0.5
ICHG (A)
-15
1
2
3
4
5
6
7
8
10.0
0
20
40
BATTERY CURRENT
ICM ACCURACY (%)
50
60
80
100
120
140
0.0
160
TIME (MINUTES)
AC-ADAPTER CURRENT (A)
FIGURE 7. ICM ACCURACY vs AC-ADAPTER CURRENT
VCOMP
ICOMP
FIGURE 8. TYPICAL CHARGING VOLTAGE AND CURRENT
ICOMP
VCOMP
CHARGE
CURRENT
CHARGE
CURRENT
INDUCTOR
CURRENT
FIGURE 9. CHARGE ENABLE
9
INDUCTOR
CURRENT
FIGURE 10. CHARGE DISABLE
FN6978.3
June 8, 2011
ISL88731C
Typical Operating Performance
UGATE
DCIN = 20V, 3S2P Li-Battery, TA = +25°C, unless otherwise noted. (Continued)
UGATE
LGATE
INDUCTOR
CURRENT
PHASE
LGATE
INDUCTOR
CURRENT
PHASE
FIGURE 11. SWITCHING WAVEFORMS AT DIODE EMULATION
FIGURE 12. SWITCHING WAVEFORMS IN CC MODE
CSON/
V BATTERY
CSON/
V BATTERY
BATTERY
CURRENT
BATTERY
CURRENT
FIGURE 13. BATTERY REMOVAL
FIGURE 14. BATTERY INSERTION
100
SYSTEM
LOAD
CHARGE
CURRENT
EFFICIENCY (%)
BATTERY
VOLTAGE
95
16.8V BATTERY
90
12.6V BATTERY
8.4V BATTERY
85
ADAPTER
CURRENT
4.2V BATTERY
80
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
IOUT (A)
FIGURE 15. LOAD TRANSIENT RESPONSE
10
FIGURE 16. EFFICIENCY vs CHARGE CURRENT AND BATTERY
VOLTAGE
FN6978.3
June 8, 2011
ISL88731C
Theory of Operation
Introduction
The ISL88731C includes all of the functions necessary to charge
1 to 4 cell Li-Ion and Li-polymer batteries. A high efficiency
synchronous buck converter is used to control the charging
voltage up to 19.2V and charging current up to 8A. The
ISL88731C also has input current limiting up to 11A. The Input
current limit, charge current limit and charge voltage limit are set
by internal registers written with SMBus. The ISL88731C “Typical
Application Circuit” is shown in Figure 4.
The ISL88731C charges the battery with constant charge current,
set by the ChargeCurrent register, until the battery voltage rises to
a voltage set by the ChargeVoltage register. The charger will then
operate at a constant voltage. The adapter current is monitored
and if the adapter current rises to the limit set by the InputCurrent
register, battery charge current is reduced so the charger does not
reduce the adapter current available to the system.
The ISL88731C features a voltage regulation loop (VCOMP) and 2
current regulation loops (ICOMP). The VCOMP voltage regulation
loop monitors VFB to limit the battery charge voltage. The ICOMP
current regulation loop limits the battery charging current
delivered to the battery to ensure that it never exceeds the
current set by the ChargeCurrent register. The ICOMP current
regulation loop also limits the input current drawn from the
AC-adapter to ensure that it never exceeds the limit set by the
InputCurrent register, and to prevent a system crash and
AC-adapter overload.
PWM Control
The ISL88731C employs a fixed frequency PWM control
architecture with a feed-forward function. The feed-forward
function maintains a constant modulator gain of 11 to achieve fast
line regulation as the input voltage changes.
The duty cycle of the buck regulator is controlled by the lower of
the voltages on ICOMP and VCOMP. The voltage on ICOMP and
VCOMP are inputs to a Lower Voltage Buffer (LVB) who’s output is
the lower of the 2 inputs. The output of the LVB is compared to an
internal 400kHz ramp to produce the Pulse Width Modulated
signal that controls the UGATE and LGATE drivers. An internal
clamp holds the higher of the 2 voltages (0.3V) above the lower
voltage. This speeds the transition from voltage loop control to
current loop control or vice versa.
The ISL88731C can operate up to 99.6% duty cycle if the input
voltage drops close to or below the battery charge voltage (drop
out mode). The DC/DC converter has a timer to prevent the
frequency from dropping into the audible frequency range.
To prevent boosting of the system bus voltage, the battery
charger drives the lower FET in a way that prevents negative
inductor current.
An adaptive gate drive scheme is used to control the dead time
between two switches. The dead time control circuit monitors the
LGATE output and prevents the upper side MOSFET from turning
on until 20ns after LGATE falls below 1V VGS, preventing
cross-conduction and shoot-through. The same occurs for LGATE
turn on. In order for the deadtime circuit to work properly, there
must be a low resistance, low inductance path from the LGATE
11
driver to MOSFET gate, and from the source of MOSFET to PGND.
An internal Schottky diode between the VDDP pin and BOOT pin
keeps the bootstrap capacitor charged.
AC-Adapter Detection
Connect the AC-adapter voltage through a resistor divider to ACIN
to detect when AC power is available, as shown in Figure 4. ACOK
is an open-drain output and is active low when ACIN is less than
Vth,fall, and high when ACIN is above Vth,rise. The ACIN rising
threshold is 3.2V (typ) with 60mV hysteresis.
Current Measurement
Use ICM to monitor the adapter current being sensed across
CSSP and CSSN. The output voltage range is 0V to 2.5V. The
voltage of ICM is proportional to the voltage drop across CSSP
and CSSN, and is given by Equation 1:
(EQ. 1)
ICM = 20 ⋅ IINPUT ⋅ R S1
where Iadapter is the DC current drawn from the AC adapter. It is
recommended to have an RC filter at the ICM output for
minimizing the switching noise.
VDDP Regulator
VDDP provides a 5.1V supply voltage from the internal LDO
regulator from DCIN and can deliver up to 30mA of continuous
current. The MOSFET drivers are powered by VDDP. VDDP also
supplies power to VCC through a low pass filter as shown in
“TYPICAL APPLICATION CIRCUIT” on page 2. Bypass VDDP and
VCC with a 1µF capacitor.
VDDSMB Supply
The VDDSMB input provides power to the SMBus interface. Connect
VDDSMB to VCC, or apply an external supply to VDDSMB. Bypass
VDDSMB to GND with a 0.1µF or greater ceramic capacitor.
The typical application connects VDDSMB to the same power source
as the SMBus master. This supply should be active and greater than
2.5V when either the adapter or the battery is present.
ISL88731C does not function when VDDSMB is below its
specified Under Voltage Lockout (UVLO) voltage. All of the SMBus
registers in ISL88731C are powered by VDDSMB and are set to
zero when it is below the UVLO threshold. Other functions are
unpredictable when VDDSMB is below the UVLO threshold.
Short Circuit Protection and 0V Battery
Charging
Since the battery charger will regulate the charge current to the
limit set by the ChargeCurrent register, it automatically has short
circuit protection and is able to provide the charge current to
wake up an extremely discharged battery. Undervoltage trickle
charge folds back current if there is a short circuit on the output.
Undervoltage Detect and Battery Trickle
Charging
If the voltage at CSON falls below 2.5V ISL88731C reduces the
charge current limit to 128mA to trickle charge the battery. When
the voltage rises above 2.7V, the charge current reverts to the
programmed value in the ChargeCurrent register.
FN6978.3
June 8, 2011
ISL88731C
Over-Temperature Protection
General SMBus Architecture
If the die temp exceeds +150°C, it stops charging. Once the die
temp drops below +125°C, charging will start up again.
VDDSMB
SMBUS SLAVE
Overvoltage Protection
INPUT
SMBUS MASTER
SCL
CONTROL
INPUT
INPUT
MACHINE,
REGISTERS,
MEMORY,
SDA
ETC
OUTPUT CONTROL
OUTPUT
CPU
SDA
CONTROL
INPUT
OUTPUT
SMBUS SLAVE
INPUT
OUTPUT
SDA
CL
INPUT
S
ISL88731C has an Overvoltage Protection circuit that limits the
output voltage when the battery is removed or disconnected by a
pulse charging circuit. If CSON exceeds the output voltage set
point in the charge voltage register by more than 300mV, an
internal comparator pulls VCOMP down and turns off both upper
and lower FETs of the buck as in Figure 17. There is a delay of
approximately 1µs between VOUT exceeding the OVP trip point
and pulling VCOMP, LGATE and UGATE low. After UGATE and
LGATE are turned OFF, inductor current continues to flow through
the body diode of the lower FET and VOUT continues to rise until
inductor current reaches zero.
STATE
SCL
OUTPUT CONTROL
OUTPUT
SCL
STATE
CONTROL
MACHINE,
REGISTERS,
SDA
MEMORY,
CONTROL
ETC
TO OTHER
SLAVE DEVICES
VOUT
INDUCTOR CURRENT
Data Validity
The data on the SDA line must be stable during the HIGH period
of the SCL, unless generating a START or STOP condition. The
HIGH or LOW state of the data line can only change when the
clock signal on the SCL line is LOW. Refer to Figure 18.
SDA
SCL
PHASE
DATA LINE CHANGE
STABLE
OF DATA
DATA VALID ALLOWED
BATTERY CURRENT
FIGURE 18. DATA VALIDITY
FIGURE 17. OVERVOLTAGE PROTECTION IN ISL88731C
START and STOP Conditions
The System Management Bus
As shown in Figure 19, START condition is a HIGH-to-LOW
transition of the SDA line while SCL is HIGH.
The System Management Bus (SMBus) is a 2-wire bus that
supports bidirectional communications. The protocol is described
briefly here. More detail is available from www.smbus.org.
The STOP condition is a LOW-to-HIGH transition on the SDA line
while SCL is HIGH. A STOP condition must be sent before each
START condition.
SDA
SCL
S
P
START
CONDITION
STOP
CONDITION
FIGURE 19. START AND STOP WAVEFORMS
12
FN6978.3
June 8, 2011
ISL88731C
Acknowledge
Once the control byte is sent, and the ISL88731C acknowledges
it, the 2nd byte sent by the master must be a register address
byte such as 0x14 for the ChargeCurrent register. The register
address byte tells the ISL88731C which register the master will
write or read. See Table 1 for details of the registers. Once the
ISL88731C receives a register address byte it responds with an
acknowledge.
Each address and data transmission uses 9-clock pulses. The
ninth pulse is the acknowledge bit (ACK). After the start
condition, the master sends 7-slave address bits and a R/W bit
during the next 8-clock pulses. During the ninth clock pulse, the
device that recognizes its own address holds the data line low
to acknowledge. The acknowledge bit is also used by both the
master and the slave to acknowledge receipt of register
addresses and data (see Figure 20).
Byte Format
Every byte put on the SDA line must be eight bits long and must
be followed by an acknowledge bit. Data is transferred with the
most significant bit first (MSB) and the least significant bit last
(LSB).
SCL
2
1
8
9
SDA
ISL88731C and SMBus
MSB
START
ACKNOWLEDGE
FROM SLAVE
The ISL88731C receives control inputs from the SMBus
interface. The serial interface complies with the SMBus protocols
as documented in the System Management Bus Specification
V1.1, which can be downloaded from www.smbus.org. The
ISL88731C uses the SMBus Read-Word and Write-Word
protocols (Figure 21) to communicate with the smart battery. The
ISL88731C is an SMBus slave device and does not initiate
communication on the bus. It responds to the 7-bit address
0b0001001_ (0x12).
FIGURE 20. ACKNOWLEDGE ON THE I2C BUS
SMBus Transactions
All transactions start with a control byte sent from the SMBus master
device. The control byte begins with a Start condition, followed by 7-bits
of slave address (0001001 for the ISL88731C) followed by the R/W bit.
The R/W bit is 0 for a write or 1 for a read. If any slave devices on the
SMBus bus recognize their address, they will Acknowledge by pulling
the serial data (SDA) line low for the last clock cycle in the control byte. If
no slaves exist at that address or are not ready to communicate, the
data line will be 1, indicating a Not Acknowledge condition.
Read address = 0b00010011 and
Write address = 0b00010010.
In addition, the ISL88731C has two identification (ID) registers: a
16-bit device ID register and a 16-bit manufacturer ID register.
TABLE 1. BATTERY CHARGER REGISTER SUMMARY
REGISTER
ADDRESS
REGISTER NAME
READ/WRITE
0x14
ChargeCurrent
Read or Write
6-bit Charge Current Setting
0x0000
0x15
ChargeVoltage
Read or Write
11-bit Charge Voltage Setting
0x0000
0x3F
InputCurrent
Read or Write
6-bit Charge Current Setting
0x0080
0xFE
ManufacturerID
Read Only
Manufacturer ID
0x0049
0xFF
DeviceID
Read Only
Device ID
0x0001
DESCRIPTION
POR STATE
Write To A Register
S
SLAVE
ADDR + W
A
REGISTER
ADDR
A
LO BYTE
DATA
A
HI BYTE
DATA
A
A
LO BYTE
DATA
P
Read From A Register
S
SLAVE
ADDR + W
A
REGISTER
ADDR
A
P
S
SLAVE
ADDR + R
A
HI BYTE
DATA
S
START
A
ACKNOWLEDGE
DRIVEN BY THE MASTER
P
STOP
N
NO ACKNOWLEDGE
DRIVEN BY ISL88731C
N
P
FIGURE 21. SMBus/ISL88731C READ AND WRITE PROTOCOL
13
FN6978.3
June 8, 2011
ISL88731C
The data (SDA) and clock (SCL) pins have Schmitt-trigger inputs
that can accommodate slow edges. Choose pull-up resistors for
SDA and SCL to achieve rise times according to the SMBus
specifications. The ISL88731C is controlled by the data written to
the registers described in Table 1.
Battery Charger Registers
The ISL88731C supports five battery-charger registers that use
either Write-Word or Read-Word protocols, as summarized in
Table 1. ManufacturerID and DeviceID are “read only” registers
and can be used to identify the ISL88731C. On the ISL88731C,
ManufacturerID always returns 0x0049 (ASCII code for “I” for
Intersil) and DeviceID always returns 0x0001.
Enabling and Disabling Charging
After applying power to ISL88731C, the internal registers contain
their POR values (see Table 1). The POR values for charge current
and charge voltage are 0x0000. These values disable charging.
To enable charging, the ChargeCurrent register must be written
with a number >0x007F and the ChargeVoltage register must be
written with a number >0x000F. Charging can be disabled by
writing 0x0000 to either of these registers.
Setting Charge Voltage
Charge voltage is set by writing a valid 16-bit number to the
ChargeVoltage register. This 16-bit number translates to a
65.535V full-scale voltage. The ISL88731C ignores the first 4
LSBs and uses the next 11 bits to set the voltage DAC. The
charge voltage range of the ISL88731C is 1.024V to 19.200V.
Numbers requesting charge voltage greater than 19.200V result
in a ChargeVoltage of 19.200V. All numbers requesting charge
voltage below 1.024V result in a voltage set point of zero, which
terminates charging. Upon initial power-up or reset, the
ChargeVoltage and ChargeCurrent registers are reset to 0 and
the charger remains shut down until valid numbers are sent to
the ChargeVoltage and ChargeCurrent registers. Use the WriteWord protocol (Figure 21) to write to the ChargeVoltage register.
The register address for ChargeVoltage is 0x15. The 16-bit binary
number formed by D15–D0 represents the charge voltage set
point in mV. However, the resolution of the ISL88731C is 16mV
because the D0–D3 bits are ignored as shown in Table 2. The
D15 bit is also ignored because it is not needed to span the
1.024V to 19.2V range. Table 2 shows the mapping between the
charge-voltage set point and the 16-bit number written to the
ChargeVoltage register. The ChargeVoltage register can be read
back to verify its contents.
TABLE 2. CHARGEVOLTAGE (REGISTER 0x15)
BIT
BIT NAME
DESCRIPTION
0
Not used.
1
Not used.
2
Not used.
3
Not used.
4
Charge Voltage, DACV 0
0 = Adds 0mV of charger voltage, 1024mV min.
1 = Adds 16mV of charger voltage.
5
Charge Voltage, DACV 1
0 = Adds 0mV of charger voltage, 1024mV min.
1 = Adds 32mV of charger voltage.
6
Charge Voltage, DACV 2
0 = Adds 0mV of charger voltage, 1024mV min.
1 = Adds 64mV of charger voltage.
7
Charge Voltage, DACV 3
0 = Adds 0mV of charger voltage, 1024mV min.
1 = Adds 128mV of charger voltage.
8
Charge Voltage, DACV 4
0 = Adds 0mV of charger voltage, 1024mV min.
1 = Adds 256mV of charger voltage.
9
Charge Voltage, DACV 5
0 = Adds 0mV of charger voltage, 1024mV min.
1 = Adds 512mV of charger voltage.
10
Charge Voltage, DACV 6
0 = Adds 0mA of charger voltage.
1 = Adds 1024mV of charger voltage.
11
Charge Voltage, DACV 7
0 = Adds 0mV of charger voltage.
1 = Adds 2048mV of charger voltage.
12
Charge Voltage, DACV 8
0 = Adds 0mV of charger voltage.
1 = Adds 4096mV of charger voltage.
13
Charge Voltage, DACV 9
0 = Adds 0mV of charger voltage.
1 = Adds 8192mV of charger voltage.
14
Charge Voltage, DACV 10
0 = Adds 0mV of charger voltage.
1 = Adds 16384mV of charger voltage, 19200mV max.
15
Not used. Normally a 32768mV weight.
14
FN6978.3
June 8, 2011
ISL88731C
Setting Charge Current
ISL88731C has a 16-bit ChargeCurrent register that sets the
battery charging current. ISL88731C controls the charge current
by controlling the CSOP-CSON voltage. The register’s LSB
translates to 10µV at CSON-CSOP. With a 10mΩ charge current
Rsense resistor (RS2 in ”Typical Application Circuit” on page 2),
the LSB translates to 1mA charge current. The ISL88731C
ignores the first 7 LSBs and uses the next 6 bits to control the
current DAC. The charge-current range of the ISL88731C is 0A to
8.064A (using a 10mΩ current-sense resistor). All numbers
requesting charge current above 8.064A result in a current
setting of 8.064A. All numbers requesting charge current
between 0mA to 128mA result in a current setting of 0mA. The
default charge current setting at Power-On Reset (POR) is 0mA.
To stop charging, set ChargeCurrent to 0. Upon initial power up,
the ChargeVoltage and ChargeCurrent registers are reset to 0
and the charger is disabled. To start the charger, write valid
numbers to the ChargeVoltage and ChargeCurrent registers. The
ChargeCurrent register uses the Write-Word protocol (Figure 21).
The register code for ChargeCurrent is 0x14 (0b00010100).
Table 3 shows the mapping between the charge current set point
and the ChargeCurrent number. The ChargeCurrent register can
be read back to verify its contents.
The ISL88731C includes a fault limiter for low battery conditions.
If the battery voltage is less than 2.5V, the charge current is
temporarily set to 128mA. The ChargeCurrent register is
preserved and becomes active again when the battery voltage is
higher than 2.7V. This function effectively provides a foldback
current limit, which protects the charger during short circuit and
overload.
TABLE 3. CHARGE CURRENT (REGISTER 0x14) (10mΩ SENSE RESISTOR, RS2)
BIT
BIT NAME
DESCRIPTION
0
Not used.
1
Not used.
2
Not used.
3
Not used.
4
Not used.
5
Not used.
6
Not used.
7
Charge Current, DACI 0
0 = Adds 0mA of charger current.
1 = Adds 128mA of charger current.
8
Charge Current, DACI 1
0 = Adds 0mA of charger current.
1 = Adds 256mA of charger current.
9
Charge Current, DACI 2
0 = Adds 0mA of charger current.
1 = Adds 512mA of charger current.
10
Charge Current, DACI 3
0 = Adds 0mA of charger current.
1 = Adds 1024mA of charger current.
11
Charge Current, DACI 4
0 = Adds 0mA of charger current.
1 = Adds 2048mA of charger current.
12
Charge Current, DACI 5
0 = Adds 0mA of charger current.
1 = Adds 4096mA of charger current, 8064mA max.
13
Not used.
14
Not used.
15
Not used.
15
FN6978.3
June 8, 2011
ISL88731C
Setting Input-Current Limit
The total power from an AC adapter is the sum of the power
supplied to the system and the power into the charger and battery.
When the input current exceeds the set input current limit, the
ISL88731C decreases the charge current to provide priority to
system load current. As the system load rises, the available charge
current drops linearly to zero. Thereafter, the total input current
can increase to the limit of the AC adapter.
The internal amplifier compares the differential voltage between
CSSP and CSSN to a scaled voltage set by the InputCurrent
register. The total input current is the sum of the device supply
current, the charger input current, and the system load current.
The total input current can be estimated as shown in Equation 2.
I INPUT = I SYSTEM + [ ( I CHARGE × V BATTERY ) ⁄ ( V IN × η ) ]
(EQ. 2)
Where η is the efficiency of the DC/DC converter (typically 85%
to 95%).
The ISL88731C has a 16-bit InputCurrent register that translates
to a 2mA LSB and a 131.071A full scale current using a 10mΩ
current-sense resistor (RS1 in Figure 4). Equivalently, the 16-bit
InputCurrent number sets the voltage across CSSP and CSSN
inputs in 20µV per LSB increments. To set the input current limit
use the SMBus to write a 16-bit InputCurrent register using the
data format listed in Table 4. The InputCurrent register uses the
Write-Word protocol (see Figure 21). The register code for
InputCurrent is 0x3F (0b00111111). The InputCurrent register
can be read back to verify its contents.
The ISL88731C ignores the first 7 LSBs and uses the next 6 bits
to control the input-current DAC. The input-current range of the
ISL88731C is from 256mA to 11.004A. All 16-bit numbers
requesting input current above 11.004A result in an inputcurrent setting of 11.004A. All 16-bit numbers requesting input
current between 0mA to 256mA result in an input-current setting
of 0mA. The default input-current-limit setting at POR is 256mA.
When choosing the current-sense resistor RS1, carefully
calculate its power rating. Take into account variations in the
system’s load current and the overall accuracy of the sense
amplifier. Note that the voltage drop across RS1 contributes
additional power loss, which reduces efficiency. System currents
normally fluctuate as portions of the system are powered up or
put to sleep. Without input current regulation, the input source
must be able to deliver the maximum system current and the
maximum charger-input current. By using the input-current-limit
circuit, the output-current capability of the AC wall adapter can
be lowered, reducing system cost.
TABLE 4. INPUT CURRENT (REGISTER 0x3F) (10mΩ SENSE RESISTOR, RS1)
BIT
BIT NAME
DESCRIPTION
0
Not used.
1
Not used.
2
Not used.
3
Not used.
4
Not used.
5
Not used.
6
Not used.
7
Input Current, DACS 0
0 = Adds 0mA of input current.
1 = Adds 256mA of input current.
8
Input Current, DACS 1
0 = Adds 0mA of input current.
1 = Adds 512mA of input current.
9
Input Current, DACS 2
0 = Adds 0mA of input current.
1 = Adds 1024mA of input current.
10
Input Current, DACS 3
0 = Adds 0mA of input current.
1 = Adds 2048mA of input current.
11
Input Current, DACS 4
0 = Adds 0mA of input current.
1 = Adds 4096mA of input current.
12
Input Current, DACS 5
0 = Adds 0mA of input current.
1 = Adds 8192mA of input current, 11004mA max.
13
Not used.
14
Not used.
15
Not used.
16
FN6978.3
June 8, 2011
ISL88731C
Charger Timeout
The ISL88731C includes 2 timers to insure the SMBus master is
active and to prevent overcharging the battery. ISL88731C will
terminate charging if the charger has not received a write to the
ChargeVoltage or ChargeCurrent register within 175s or if the
SCL line is low for more than 25ms. If a time-out occurs, either
ChargeVoltage or ChargeCurrent registers must be written to reenable charging.
ISL88731C Data Byte Order
Each register in ISL88731C contains 16-bits or 2, 8 bit bytes. All
data sent on the SMBus is in 8-bit bytes and 2 bytes must be
written or read from each register in ISL88731C. The order in
which these bytes are transmitted appears reversed from the
way they are normally written. The LOW byte is sent first and the
HI byte is sent second. For example, when writing 0x41A0, 0xA0
is written first and 0x41 is sent second.
Writing to the Internal Registers
In order to set the charge current, charge voltage or input current,
valid 16-bit numbers must be written to ISL88731C’s internal
registers via the SMBus.
To write to a register in the ISL88731C, the master sends a
control byte with the R/W bit set to 0, indicating a write. If it
receives an Acknowledge from the ISL88731C it sends a register
address byte setting the register to be written (i.e., 0x14 for the
ChargeCurrent register). The ISL88731C will respond with an
Acknowledge. The master then sends the lower data byte to be
written into the desired register. The ISL88731C will respond with
an Acknowledge. The master then sends the higher data byte to
be written into the desired register. The ISL88731C will respond
with an Acknowledge. The master then issues a Stop condition,
indicating to the ISL88731C that the current transaction is
complete. Once this transaction completes the ISL88731C will
begin operating at the new current or voltage.
ISL88731C does not support writing more than one register per
transaction.
Reading from the Internal
Registers
The ISL88731C has the ability to read from 5 internal registers.
Prior to reading from an internal register, the master must first
select the desired register by writing to it and sending the registers
address byte. This process begins by the master sending a control
byte with the R/W bit set to 0, indicating a write. Once it receives
an Acknowledge from the ISL88731C it sends a register address
byte representing the internal register it wants to read. The
ISL88731C will respond with an Acknowledge. The master must
then respond with a Stop condition. After the Stop condition the
master follows with a new Start condition, then sends a new
control byte with the ISL88731C slave address and the R/W bit set
to 1, indicating a read. The ISL88731C will Acknowledge then send
the lower byte stored in that register. After receiving the byte, the
master Acknowledges by holding SDA low during the 9th clock
pulse. ISL88731C then sends the higher byte stored in the register.
After the second byte neither device holds SDA low (No
17
Acknowledge). The master will then produce a Stop condition to
end the read transaction.
ISL88731C does not support reading more than 1 register per
transaction.
Application Information
The following battery charger design refers to the “Typical
Application Circuit” (see Figure 4), where typical battery
configuration of 3S2P is used. This section describes how to
select the external components including the inductor, input and
output capacitors, switching MOSFETs and current sensing
resistors.
Inductor Selection
The inductor selection has trade-offs between cost, size,
crossover frequency and efficiency. For example, the lower the
inductance, the smaller the size, but ripple current is higher. This
also results in higher AC losses in the magnetic core and the
windings, which decreases the system efficiency. On the other
hand, the higher inductance results in lower ripple current and
smaller output filter capacitors, but it has higher DCR (DC
resistance of the inductor) loss, lower saturation current and has
slower transient response. So, the practical inductor design is
based on the inductor ripple current being ±15% to ±20% of the
maximum operating DC current at maximum input voltage.
Maximum ripple is at 50% duty cycle or VBAT = VIN,MAX/2. The
required inductance for ±15% ripple current can be calculated
from Equation 3:
V IN, MAX
L = ------------------------------------------------------4 ⋅ F SW ⋅ 0.3 ⋅ I L, MAX
(EQ. 3)
Where VIN,MAX is the maximum input voltage, FSW is the
switching frequency and IL,MAX is the max DC current in the
inductor.
For VIN,MAX = 20V, VBAT = 12.6V, IBAT,MAX = 4.5A, and
fs = 400kHz, the calculated inductance is 9.3µH. Choosing the
closest standard value gives L = 10µH. Ferrite cores are often the
best choice since they are optimized at 400kHz to 600kHz
operation with low core loss. The core must be large enough not
to saturate at the peak inductor current IPeak in Equation 4:
1
I PEAK = I L, MAX + --- ⋅ I RIPPLE
2
(EQ. 4)
Inductor saturation can lead to cascade failures due to very high
currents. Conservative design limits the peak and RMS current in
the inductor to less than 90% of the rated saturation current.
Crossover frequency is heavily dependent on the inductor value.
FCO should be less than 20% of the switching frequency and a
conservative design has FCO less than 10% of the switching
frequency. The highest FCO is in voltage control mode with the
battery removed and may be calculated (approximately) from
Equation 5:
5 ⋅ 11 ⋅ RS2
F CO = ------------------------------2π ⋅ L
(EQ. 5)
FN6978.3
June 8, 2011
ISL88731C
Output Capacitor Selection
The output capacitor in parallel with the battery is used to absorb
the high frequency switching ripple current and smooth the
output voltage. The RMS value of the output ripple current IRMS
is given by Equation 6:
V IN, MAX
I ( Cout ) RMS = ---------------------------------- ⋅ D ⋅ ( 1 – D )
12 ⋅ L ⋅ F SW
(EQ. 6)
Where the duty cycle D is the ratio of the output voltage (battery
voltage) over the input voltage for continuous conduction mode
which is typical operation for the battery charger. During the
battery charge period, the output voltage varies from its initial
battery voltage to the rated battery voltage. So, the duty cycle
varies from 0.53 for the minimum battery voltage of 7.5V
(2.5V/Cell) to 0.88 for the maximum battery voltage of 12.6V.
The maximum RMS value of the output ripple current occurs at
the duty cycle of 0.5 and is expressed as Equation 7:
V IN, MAX
I ( Cout ) RMS = -----------------------------------------4 ⋅ 12 ⋅ L ⋅ F SW
(EQ. 7)
For VIN,MAX = 19V, VBAT = 16.8V, L = 10µH, and fs = 400kHz, the
maximum RMS current is 0.19A. A typical 20µF ceramic
capacitor is a good choice to absorb this current and also has
very small size. Organic polymer capacitors have high
capacitance with small size and have a significant equivalent
series resistance (ESR). Although ESR adds to ripple voltage, it
also creates a high frequency zero that helps the closed loop
operation of the buck regulator.
EMI considerations usually make it desirable to minimize ripple
current in the battery leads. Beads may be added in series with
the battery pack to increase the battery impedance at 400kHz
switching frequency. Switching ripple current splits between the
battery and the output capacitor depending on the ESR of the
output capacitor and battery impedance. If the ESR of the output
capacitor is 10mΩ and battery impedance is raised to 2Ω with a
bead, then only 0.5% of the ripple current will flow in the battery.
MOSFET Selection
The Notebook battery charger synchronous buck converter has
the input voltage from the AC-adapter output. The maximum
AC-adapter output voltage does not exceed 25V. Therefore, 30V
logic MOSFET should be used.
The high-side MOSFET must be able to dissipate the conduction
losses plus the switching losses. For the battery charger
application, the input voltage of the synchronous buck converter is
equal to the AC-adapter output voltage, which is relatively
constant. The maximum efficiency is achieved by selecting a high
side MOSFET that has the conduction losses equal to the switching
losses. Switching losses in the low-side FET are very small. The
choice of low-side FET is a trade-off between conduction losses
(rDS(ON)) and cost. A good rule of thumb for the rDS(ON) of the
low-side FET is 2x the rDS(ON) of the high-side FET.
The LGATE gate driver can drive sufficient gate current to switch
most MOSFETs efficiently. However, some FETs may exhibit cross
conduction (or shoot-through) due to current injected into the
drain-to-source parasitic capacitor (Cgd) by the high dv/dt rising
edge at the phase node when the high side MOSFET turns on.
18
Although LGATE sink current (1.8A typical) is more than enough
to switch the FET off quickly, voltage drops across parasitic
impedances between LGATE and the MOSFET can allow the gate
to rise during the fast rising edge of voltage on the drain.
MOSFETs with low threshold voltage (<1.5V) and low ratio of
Cgs/Cgd (<5) and high gate resistance (>4Ω) may be turned on
for a few ns by the high dv/dt (rising edge) on their drain. This can
be avoided with higher threshold voltage and Cgs/Cgd ratio.
Another way to avoid cross conduction is slowing the turn-on
speed of the high-side MOSFET by connecting a resistor between
the BOOT pin and the bootstrap capacitor.
For the high-side MOSFET, the worst-case conduction losses
occur at the minimum input voltage, as shown in Equation 8:
V OUT
2
P Q1, conduction = ------------- ⋅ I BAT ⋅ r DS ( ON )
V IN
(EQ. 8)
The optimum efficiency occurs when the switching losses equal
the conduction losses. However, it is difficult to calculate the
switching losses in the high-side MOSFET since it must allow for
difficult-to-quantify factors that influence the turn-on and turn-off
times. These factors include the MOSFET internal gate
resistance, gate charge, threshold voltage, stray inductance and
the pull-up and pull-down resistance of the gate driver.
The following switching loss calculation (Equation 9) provides a
rough estimate.
P Q1, Switching =
⎛ Q gd ⎞ 1
⎛ Q gd ⎞
1
-⎟ + --- V IN I LP f sw ⎜ ----------------⎟ + Q rr V IN f sw
--- V IN I LV f sw ⎜ ----------------------2
⎝ I g, source⎠ 2
⎝ I g, sin k⎠
(EQ. 9)
Where the following are the peak gate-drive source/sink current
of Q1, respectively:
•
•
•
•
•
•
Qgd: drain-to-gate charge,
Qrr: total reverse recovery charge of the body-diode in low-side
MOSFET,
ILV: inductor valley current,
ILP: Inductor peak current,
Ig,sink
Ig,source
Low switching loss requires low drain-to-gate charge Qgd.
Generally, the lower the drain-to-gate charge, the higher the
ON-resistance. Therefore, there is a trade-off between the
ON-resistance and drain-to-gate charge. Good MOSFET selection
is based on the Figure of Merit (FOM), which is a product of the
total gate charge and on-resistance. Usually, the smaller the
value of FOM, the higher the efficiency for the same application.
For the low-side MOSFET, the worst-case power dissipation
occurs at minimum battery voltage and maximum input voltage
as shown in Equation 10.
V OUT⎞
⎛
2
P Q2 = ⎜ 1 – -------------⎟ ⋅ I BAT ⋅ r DS ( ON )
V IN ⎠
⎝
(EQ. 10)
Choose a low-side MOSFET that has the lowest possible
ON-resistance with a moderate-sized package (like the 8 Ld
SOIC) and is reasonably priced. The switching losses are not an
issue for the low-side MOSFET because it operates at
zero-voltage-switching.
FN6978.3
June 8, 2011
ISL88731C
Ensure that the required total gate drive current for the selected
MOSFETs should be less than 24mA. Thus, the total gate charge
for the high-side and low-side MOSFETs is limited by Equation 11:
I GATE
Q GATE ≤ -------------F SW
(EQ. 11)
Where IGATE is the total gate drive current and should be less
than 24mA. Substituting IGATE = 24mA and fs = 400kHz into
Equation 11 yields that the total gate charge should be less than
80nC. Therefore, the ISL88731C easily drives the battery charge
current up to 8A.
Snubber Design
ISL88731C's buck regulator operates in discontinuous current
mode (DCM) when the load current is less than half the
peak-to-peak current in the inductor. After the low-side FET turns
off, the phase voltage rings due to the high impedance with both
FETs off. This can be seen in Figure 11. Adding a snubber
(resistor in series with a capacitor) from the phase node to
ground can greatly reduce the ringing. In some situations, a
snubber can improve output ripple and regulation.
The snubber capacitor should be approximately twice the
parasitic capacitance on the phase node. This can be estimated
by operating at very low load current (100mA) and measuring the
ringing frequency.
CSNUB and RSNUB can be calculated from Equations 12 and 13:
2
C SNUB = -----------------------------------2
( 2πF ring ) ⋅ L
Transconductance Amplifiers GMV, GMI and
GMS
ISL88731C uses several transconductance amplifiers (also
known as gm amps). Most commercially available op amps are
voltage controlled voltage sources with gain expressed as
A = VOUT/VIN. gm amps are voltage controlled current sources
with gain expressed as gm = IOUT/VIN. gm will appear in some of
the equations for poles and zeros in the compensation.
PWM Gain Fm
The Pulse Width Modulator in the ISL88731C converts voltage at
VCOMP to a duty cycle by comparing VCOMP to a triangle wave
(duty = VCOMP/VP-P RAMP). The low-pass filter formed by L and
CO convert the duty cycle to a DC output voltage
(Vo = VDCIN*duty). In ISL88731C, the triangle wave amplitude is
proportional to VDCIN. Making the ramp amplitude proportional
to DCIN makes the gain from VCOMP to the PHASE output a
constant 11 and is independent of DCIN. For small signal AC
analysis, the battery is modeled by its internal resistance. The
total output resistance is the sum of the sense resistor and the
internal resistance of the MOSFETs, inductor and capacitor.
Figure 22 shows the small signal model of the pulse width
modulator (PWM), power stage, output filter and battery.
VADAPTER
2⋅L
----------------C SNUB
(EQ. 13)
RAMP GEN
VRAMP = VADAPTER/11
-
Input Capacitor Selection
The input capacitor absorbs the ripple current from the
synchronous buck converter, which is given by Equation 14:
V OUT ( V IN – V OUT )
I RMS = I BAT -------------------------------------------------V IN
+
L
DRIVERS
R SNUB =
(EQ. 12)
controls the output is determined by the minimum current buffer
and the minimum voltage buffer shown in the “FUNCTIONAL
BLOCK DIAGRAM” on page 2. These three loops will be described
separately.
CO
PWM
INPUT
(EQ. 14)
This RMS ripple current must be smaller than the rated RMS
current in the capacitor data sheet. Non-tantalum chemistries
(ceramic, aluminum, or OSCON) are preferred due to their
resistance to power-up surge currents when the AC-adapter is
plugged into the battery charger. For Notebook battery charger
applications, it is recommended that ceramic capacitors or
polymer capacitors from Sanyo be used due to their small size
and reasonable cost.
PWM
GAIN = 11
L
RS2
11
RFET_RDSON
RL_DCR
PWM
INPUT
CO
RBAT
RESR
Loop Compensation Design
ISL88731C has three closed loop control modes. One controls
the output voltage when the battery is fully charged or absent. A
second controls the current into the battery when charging and
the third limits current drawn from the adapter. The charge
current and input current control loops are compensated by a
single capacitor on the ICOMP pin. The voltage control loop is
compensated by a network on the VCOMP pin. Descriptions of
these control loops and guidelines for selecting compensation
components will be given in the following sections. Which loop
19
FIGURE 22. SMALL SIGNAL AC MODEL
In most cases the Battery resistance is very small (<200mΩ)
resulting in a very low Q in the output filter. This results in a
frequency response from the input of the PWM to the inductor
current with a single pole at the frequency calculated in
Equation 15:
( RS2 + r DS ( ON ) + R DCR + R BAT )
F POLE1 = ------------------------------------------------------------------------------------2π ⋅ L
(EQ. 15)
FN6978.3
June 8, 2011
ISL88731C
The output capacitor creates a pole at a very high frequency due
to the small resistance in parallel with it. The frequency of this
pole is calculated in Equation 16:
11 ⋅ RS2
A DC = ------------------------------------------------------------------------------------( RS2 + r DS ( ON ) + R DCR + R BAT )
(EQ. 20)
1
F POLE2 = -----------------------------------2π ⋅ C o ⋅ R BAT
11 ⋅ RS2
F CO = A DC ⋅ F POLE = ----------------------2π ⋅ L
(EQ. 21)
(EQ. 16)
Charge Current Control Loop
When the battery is less than the fully charged, the voltage error
amplifier goes to it’s maximum output (limited to 0.3V above
ICOMP) and the ICOMP voltage controls the loop through the
minimum voltage buffer. Figure 24 shows the charge current
control loop.
The compensation capacitor (CICOMP) gives the error amplifier
(GMI) a pole at a very low frequency (<<1Hz) and a zero at FZ1.
FZ1 is created by the 0.25*CA2 output added to ICOMP. The
frequency can be calculated from Equation 17:
(EQ. 17)
gm2 = 50μA ⁄ V
Adapter Current Limit Control Loop
If the combined battery charge current and system load current
draws current that equals the adapter current limit set by the
InputCurrent register, ISL88731C will reduce the current to the
battery and/or reduce the output voltage to hold the adapter
current at the limit. Above the adapter current limit the minimum
current buffer equals the output of GMS and ICOMP controls the
charger output. Figure 25 shows the adapter current limit control
loop.
60
Placing this zero at a frequency equal to the pole calculated in
Equation 16 will result in maximum gain at low frequencies and
phase margin near 90°. If the zero is at a higher frequency
(smaller CICOMP), the DC gain will be higher but the phase
margin will be lower. Use a capacitor on ICOMP that is equal to or
greater than the value calculated in Equation 18. The factor of
1.5 is to ensure the zero is at a frequency lower than the pole
including tolerance variations.
20
0
FPOLE1
-20
L
PHASE
FZERO
40
GAIN (dB)
4 ⋅ gm2
F ZERO = ------------------------------------( 2π ⋅ C ICOMP )
The Bode plot of the loop gain, the compensator gain and the
power stage gain is shown in Figure 24.
FFILTER
11
COMPENSATOR
-40
RL_DCR
RFET_RDSON
MODULATOR
FPOLE2
LOOP
Σ
+
ΣS
CA2
+
0.25
-
GMI
ICOMP
+
RF2
CSOP
20X
-
-60
0.01k
CF2
RS2
CSON
DACI
CICOMP
CO
0.1k
1k
DCIN
RFET_RDSON
RF1
(EQ. 18)
A filter should be added between RS2 and CSOP and CSON to
reduce switching noise. The filter roll-off frequency should be
between the crossover frequency and the switching frequency
(~100kHz). RF2 should be small (<10Ω) to minimize offsets due
to leakage current into CSOP. The filter cutoff frequency is
calculated using Equation 19:
(EQ. 19)
The crossover frequency is determined by the DC gain of the
modulator and output filter and the pole in Equation 16. The DC
gain is calculated in Equation 20 and the cross over frequency is
calculated with Equation 21:
L
PHASE
11
FIGURE 23. CHARGE CURRENT LIMIT LOOP
20
1M
FIGURE 24. CHARGE CURRENT LOOP BODE PLOTS
RS1
1
F FILTER = ----------------------------------------( 2π ⋅ C F2 ⋅ R F2 )
100k
RBAT
RESR
1.5 ⋅ 4 ⋅ ( 50μA ⁄ V ) ⋅ L
C ICOMP = ------------------------------------------------------------------------------------( RS2 + r DS ( ON ) + R DCR + R BAT )
10k
FREQUENCY (Hz)
CF1
ΣS
CSSN
CSSP
+
0.25
-
CA2
+
20X
-
- 20
+
RF2
CSOP
CF2
CO
RBAT
RESR
-
+
RS2
CSON
CA1
GMS
ICOMP
RL_DCR
DACS
CICOMP
FIGURE 25. ADAPTER CURRENT LIMIT LOOP
FN6978.3
June 8, 2011
ISL88731C
The loop response equations, bode plots and the selection of
CICOMP are the same as the charge current control loop with loop
gain reduced by the duty cycle and the ratio of RS1/RS2. In other
words, if RS1 = RS2 and the duty cycle D = 50%, the loop gain will
be 6dB lower than the loop gain in Figure 25. This gives lower
crossover frequency and higher phase margin in this mode. If
RS1/RS2 = 2 and the duty cycle is 50% then the adapter current
loop gain will be identical to the gain in Figure 25.
A filter should be added between RS1 and CSIP and CSIN to reduce
switching noise. The filter roll off frequency should be between the
cross over frequency and the switching frequency (~100kHz).
When the battery is charged to the voltage set by ChargeVoltage
register, the voltage error amplifier (GMV) takes control of the
output (assuming that the adapter current is below the limit set
by ACLIM). The voltage error amplifier (GMV) discharges the cap
on VCOMP to limit the output voltage. The current to the battery
decreases as the cells charge to the fixed voltage and the voltage
across the internal battery resistance decreases. As battery
current decreases the 2 current error amplifiers (GMI and GMS)
output their maximum current and charge the capacitor on
ICOMP to its maximum voltage (limited to 0.3V above VCOMP).
With high voltage on ICOMP, the minimum voltage buffer output
equals the voltage on VCOMP.
The voltage control loop is shown in Figure 26.
L
11
RL_DCR
RFET_RDSON
CA2
+
20x
-
CF2
R3
-
CO
GMV
+
R4
CVCOMP
1
ω LC = ----------------------( L ⋅ Co )
L
Q = R o ⋅ -----Co
(EQ. 22)
The resistance RO is a combination of MOSFET rDS(ON), inductor
DCR, RSENSE and the internal resistance of the battery (normally
between 50mΩ and 200mΩ) The worst case for voltage mode
control is when the battery is absent. This results in the highest Q
of the LC filter and the lowest phase margin.
The compensation network consists of the voltage error amplifier
GMV and the compensation network RVCOMP, CVCOMP which give
the loop very high DC gain, a very low frequency pole and a zero
at FZERO1. Inductor current information is added to the feedback
to create a second zero FZERO2. The low pass filter RF2, CF2
between RS2 and ISL88731C add a pole at FFILTER. R3 and R4
are internal divider resistors that set the DC output voltage. For a
3-cell battery, R3 = 500kΩ and R4 = 100kΩ. The following
equations relate the compensation network’s poles, zeros and
gain to the components in Figure 26. Figure shows an asymptotic
Bode plot of the DC/DC converter’s gain vs. frequency. It is
strongly recommended that FZERO1 is approximately 30% of FLC
and FZERO2 is approximately 70% of FLC.
RF2
CSOP
RS2
CSON
VCOMP
s ⎞
⎛ 1 – ------------⎝
ω ESR⎠
A LC = --------------------------------------------------------⎛ s2
⎞
s
⎜ ----------- + ----------------------- + 1⎟
ω
ω
(
⋅
Q
)
⎝ DP
⎠
LC
RBAT
NO BATTERY
GAIN (dB)
PHASE
ΣS
The gain from the phase node to the system output and battery
depend entirely on external components. Typical output LC filter
response is shown in Figure 27. Transfer function ALC(s) is shown
in Equation 22:
1
ω ESR = ----------------------------( R ESR ⋅ C o )
Voltage Control Loop
+
0.25
-
Output LC Filter Transfer Functions
RESR
RBATTERY = 200mΩ
RBATTERY = 50mΩ
DACV
RVCOMP
PHASE (°)
FIGURE 26. VOLTAGE CONTROL LOOP
FREQUENCY (Hz)
FIGURE 27. FREQUENCY RESPONSE OF THE LC OUTPUT FILTER
21
FN6978.3
June 8, 2011
ISL88731C
60
PCB Layout Considerations
COMPENSATOR
Power and Signal Layers Placement on the
PCB
MODULATOR
40
LOOP
FLC
FPOLE1
As a general rule, power layers should be close together, either
on the top or bottom of the board, with signal layers on the
opposite side of the board. As an example, layer arrangement on
a 4-layer board is shown in the following:
GAIN (dB)
20
0
FFILTER
1. Top Layer: signal lines, or half board for signal lines and the
other half board for power lines
-20
FZERO1
2. Signal Ground
FZERO2
-40
3. Power Layers: Power Ground
FESR
-60
0.1k
1k
10k
100k
4. Bottom Layer: Power MOSFET, Inductors and other Power
traces
1M
FREQUENCY (Hz)
FIGURE 28. ASYMPTOTIC BODE PLOT OF THE VOLTAGE CONTROL
LOOP GAIN
Compensation Break Frequency Equations
1
F ZERO1 = ----------------------------------------------------------------( 2π ⋅ C VCOMP ⋅ R VCOMP )
⎛ R VCOMP ⎞ ⎛ R 4 ⎞ gm1
F ZERO2 = ⎜ ----------------------------------⎟ ⋅ ⎜ --------------------⎟ ⋅ ⎛ ------------⎞
⎝ 2π ⋅ RS2 ⋅ C o⎠ ⎝ R 4 + R 3⎠ ⎝ 5 ⎠
(EQ. 23)
Separate the power voltage and current flowing path from the
control and logic level signal path. The controller IC will stay on
the signal layer, which is isolated by the signal ground to the
power signal traces.
Component Placement
The power MOSFET should be close to the IC so that the gate drive
signal, the LGATE, UGATE, PHASE, and BOOT, traces can be short.
Place the components in such a way that the area under the IC
has less noise traces with high dv/dt and di/dt, such as gate
signals and phase node signals.
(EQ. 24)
Signal Ground and Power Ground Connection
At minimum, a reasonably large area of copper, which will shield
other noise couplings through the IC, should be used as signal
ground beneath the IC. The best tie-point between the signal
ground and the power ground is at the negative side of the output
capacitor on each side, where there is little noise; a noisy trace
beneath the IC is not recommended.
1
F LC = -----------------------------( 2π L ⋅ C o )
(EQ. 25)
1
F FILTER = ----------------------------------------( 2π ⋅ R F2 ⋅ C F2 )
(EQ. 26)
1
F POLE1 = --------------------------------------( 2π ⋅ RS2 ⋅ C o )
(EQ. 27)
GND and VCC Pin
1
F ESR = ----------------------------------------( 2π ⋅ C o ⋅ R ESR )
(EQ. 28)
At least one high quality ceramic decoupling capacitor should be
used to cross these two pins. The decoupling capacitor can be
put close to the IC.
Choose RVCOMP equal or lower than the value calculated from
Equation 29.
⎛ R 3 + R 4⎞
5
R VCOMP = ( 0.7 ⋅ F LC ) ⋅ ( 2π ⋅ C o ⋅ RS2 ) ⋅ ⎛ ------------⎞ ⋅ ⎜ --------------------⎟
⎝ gm1⎠ ⎝ R
4 ⎠
(EQ. 29)
Next, choose CVCOMP equal or higher than the value calculated
from Equation 30.
1
C VCOMP = ---------------------------------------------------------------------( 0.3 ⋅ F LC ) ⋅ ( 2π ⋅ R VCOMP )
22
(EQ. 30)
LGATE Pin
This is the gate drive signal for the bottom MOSFET of the buck
converter. The signal going through this trace has both high dv/dt
and high di/dt, and the peak charging and discharging current is
very high. These two traces should be short, wide, and away from
other traces. There should be no other traces in parallel with
these traces on any layer.
PGND Pin
PGND pin should be laid out to the negative side of the relevant
output capacitor with separate traces. The negative side of the
output capacitor must be close to the source node of the bottom
MOSFET. This trace is the return path of LGATE.
FN6978.3
June 8, 2011
ISL88731C
PHASE Pin
This trace should be short, and positioned away from other weak
signal traces. This node has a very high dv/dt with a voltage
swing from the input voltage to ground. No trace should be in
parallel with it. This trace is also the return path for UGATE.
Connect this pin to the high-side MOSFET source.
UGATE Pin
This pin has a square shape waveform with high dv/dt. It
provides the gate drive current to charge and discharge the top
MOSFET with high di/dt. This trace should be wide, short, and
away from other traces, similar to the LGATE.
BOOT Pin
This pin’s di/dt is as high as the UGATE; therefore, this trace
should be as short as possible.
H IG H
CU RRENT
TR AC E
SENSE
R E S IS T O R
H IG H
CU RR ENT
TRAC E
K E L V IN C O N N E C T IO N T R A C E S
T O T H E L O W P A S S F IL T E R A N D
C SO P AN D CSO N
FIGURE 29. CURRENT SENSE RESISTOR LAYOUT
resistor should start at the pads of the sense resistor and should
be routed close together, through the low pass filter and to the
CSOP and CSON pins (see Figure 29). The CSON pin is also used
as the battery voltage feedback. The traces should be routed
away from the high dv/dt and di/dt pins like PHASE, BOOT pins.
In general, the current sense resistor should be close to the IC.
These guidelines should also be followed for the adapter current
sense resistor and CSSP and CSSN. Other layout arrangements
should be adjusted accordingly.
DCIN Pin
This pin connects to AC-adapter output voltage, and should be
less noise sensitive.
Copper Size for the Phase Node
The capacitance of PHASE should be kept very low to minimize
ringing. It would be best to limit the size of the PHASE node
copper in strict accordance with the current and thermal
management of the application.
Identify the Power and Signal Ground
The input and output capacitors of the converters, the source
terminal of the bottom switching MOSFET PGND should connect
to the power ground. The other components should connect to
signal ground. Signal and power ground are tied together at one
point.
CSOP, CSON, CSSP and CSSN Pins
Clamping Capacitor for Switching MOSFET
Accurate charge current and adapter current sensing is critical
for good performance. The current sense resistor connects to the
CSON and the CSOP pins through a low pass filter with the filter
capacitor very near the IC (see Figure 4). Traces from the sense
It is recommended that ceramic capacitors be used closely
connected to the drain of the high-side MOSFET, and the source
of the low-side MOSFET. This capacitor reduces the noise and the
power loss of the MOSFET.
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Intersil products are manufactured, assembled and tested utilizing ISO9000 quality systems as noted
in the quality certifications found at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time
without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be
accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third
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23
FN6978.3
June 8, 2011
ISL88731C
Revision History
The revision history provided is for informational purposes only and is believed to be accurate, but not warranted. Please go to web to make
sure you have the latest Rev.
DATE
REVISION
CHANGE
5/25/11
FN6978.3
Removed ICM OFFSET spec line from EC table
Removed upper and lower ICM gain limits
Changed Elect Specs Note 7, from: "Compliance to datasheet limits is assured by one or more methods:
production test, characterization and/or design” to:
Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature
limits established by characterization and are not production tested.
1/14/11
FN6978.2
Revised “VDDSMB Supply” on page 11 from:
“The VDDSMB input provides power to the SMBus interface. Connect VDDSMB to VCC, or apply an external
supply to VDDSMB to keep the SMBus interface active while the supply to DCIN is removed. When VDDSMB is
biased the internal registers are maintained. Bypass VDDSMB to GND with a 0.1µF or greater ceramic
capacitor.”
to:
“The VDDSMB input provides power to the SMBus interface. Connect VDDSMB to VCC, or apply an external
supply to VDDSMB. Bypass VDDSMB to GND with a 0.1µF or greater ceramic capacitor.
The typical application connects VDDSMB to the same power source as the SMBus master. This supply should
be active and greater than 2.5V when either the adapter or the battery is present.
ISL88731C does not function when VDDSMB is below its specified Under Voltage Lockout (UVLO) voltage. All of
the SMBus registers in ISL88731C are powered by VDDSMB and are set to zero when it is below the UVLO
threshold. Other functions are unpredictable when VDDSMB is below the UVLO threshold.”
12/9/10
VDDSMB UVLO Hysteresis limits updated to reflect actual test results
From (100, 150, 200 mV) to (40, 100, 150mV)
Added to Pin 3 VREF Pin Description on page 3 “It is internally compensated. Do not connect a decoupling
capacitor.”
12/3/10
-Converted to New Intersil Template
-Updated Related Literature's Application Note's Title to match application note
-Changed copyright to legal's suggested verbiage
-On page 2, Figure 3, Functional Block Diagram, ACOK comparator input changed from REF to 3.2V. "REF" was
a typo.
-Added Eval board to ordering information
-ACOK Leakage Current Test condition in Electrical Spec Table on page 7 changed from
ACIN = 2.5V to 3.7V. 3.7V has always been the test condition on this part.
-Removed Note: Limits established by characterization and are not production tested (no longer an Intersil
standard) and all references to it in switching regulators UGate and Lgate
-Changed Note:
Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature
limits established by characterization and are not production tested.
to new standard note:
Compliance to datasheet limits is assured by one or more methods: production test, characterization and/or
design.
8/23/10
FN6978.1
Added “Overvoltage Protection” on page 12 and Figure 17“OVERVOLTAGE PROTECTION IN ISL88731C” to
page 12.
3/8/10
FN6978.0
Initial release.
Products
Intersil Corporation is a leader in the design and manufacture of high-performance analog semiconductors. The Company's products
address some of the industry's fastest growing markets, such as, flat panel displays, cell phones, handheld products, and notebooks.
Intersil's product families address power management and analog signal processing functions. Go to www.intersil.com/products for a
complete list of Intersil product families.
*For a complete listing of Applications, Related Documentation and Related Parts, please see the respective device information page
on intersil.com: ISL88731C
To report errors or suggestions for this datasheet, please go to www.intersil.com/askourstaff
FITs are available from our website at http://rel.intersil.com/reports/search.php
24
FN6978.3
June 8, 2011
ISL88731C
Package Outline Drawing
L28.5x5B
28 LEAD THIN QUAD FLAT NO-LEAD PLASTIC PACKAGE
Rev 1, 10/07
4X 3.0
5.00
24X 0.50
A
B
6
PIN 1
INDEX AREA
6
PIN #1 INDEX AREA
28
22
1
5.00
21
3 .25 ± 0 . 10
15
(4X)
7
0.15
8
14
TOP VIEW
0.10 M C A B
28X 0.55 ± 0.05
4 28X 0.25 ± 0.05
BOTTOM VIEW
SEE DETAIL "X"
0.10 C
0 . 75 ± 0.05
C
BASE PLANE
SEATING PLANE
0.08 C
( 4. 65 TYP )
( 24X 0 . 50)
(
SIDE VIEW
3. 25)
(28X 0 . 25 )
C
0 . 2 REF
5
0 . 00 MIN.
0 . 05 MAX.
( 28X 0 . 75)
TYPICAL RECOMMENDED LAND PATTERN
DETAIL "X"
NOTES:
1. Dimensions are in millimeters.
Dimensions in ( ) for Reference Only.
2. Dimensioning and tolerancing conform to AMSE Y14.5m-1994.
3. Unless otherwise specified, tolerance : Decimal ± 0.05
4. Dimension b applies to the metallized terminal and is measured
between 0.15mm and 0.30mm from the terminal tip.
5. Tiebar shown (if present) is a non-functional feature.
6. The configuration of the pin #1 identifier is optional, but must be
located within the zone indicated. The pin #1 identifier may be
either a mold or mark feature.
25
FN6978.3
June 8, 2011
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