bq2057
Advanced Li-Ion Linear Charge
Management IC
Features
General Description
➤ Ideal for single- and dual-cell Li-Ion
packs with coke or graphite anodes
The BENCHMARQ bq2057 series
advanced Li-Ion linear charge-management ICs are designed for
cost-sensitive and compact portable
electronics. They combine high-accuracy current and voltage regulation,
battery conditioning, temperature
monitoring, charge termination,
ch a r g e - s t a t u s i n d i c a t i o n , a n d
AutoComp charge-rate compensation in a single 8-pin IC.
➤ Dropout voltage as low as 0.3V
➤ AutoComp™ dynamic compensation of battery pack’s internal impedance
➤ Optional temperature-monitoring
before and during charge
➤ Integrated voltage and current
regulation with programmable
charge-current and high- or
low-side current sensing
➤ Integrated cell conditioning for
reviving deeply discharged cells
and minimizing heat dissipation
during initial stage of charge
➤ Better than ±1% voltage regulation accuracy
➤ Charge status output for LED or
host processor interface
➤ Automatic battery-recharge feature
➤ Charge termination by minimum
current
➤ Low-power sleep mode
The bq2057 continuously measures
battery temperature using an external thermistor. For safety reasons,
the bq2057 inhibits charge until the
battery temperature is within
user-defined thresholds. The bq2057
then charges the battery in three
phases: conditioning, constant current, and constant voltage. If the
battery voltage is below the
low-voltage threshold V MIN, the
bq2057 trickle-charges to condition
the battery. The conditioning charge
rate is set at 10% of the regulation
current. The conditioning current
also minimizes heat dissipation in
the external pass-element during
the initial stage of charge.
➤ Packaging: 8-pin SOIC, 8-pin
TSSOP
After conditioning, the bq2057 applies a constant current to the battery. An external sense-resistor sets
Pin Connections
Pin Names
SNS
1
8
COMP
BAT
2
7
CC
VCC
3
6
VSS
TS
4
5
STAT
the magnitude of the current. The
sense-resistor can be on either the
low or the high side of the battery
without additional components. The
constant-current phase continues
until the battery reaches the
charge-regulation voltage.
The bq2057 then begins the constant-voltage phase. The accuracy of
the voltage regulation is better than
±1% over the operating-temperature
and supply-voltage ranges. For single and dual cells with either coke
or graphite anodes, the bq2057 is offered in four fixed-voltage versions:
4.1V, 4.2V, 8.2V, and 8.4V. Charge
stops when the current tapers to the
ch a r g e t e r m i n a t i o n t h r e s h o l d ,
VTERM. The bq2057 automatically
restarts the charge if the battery
voltage falls below the VRCH threshold.
The designer also may use the
AutoComp feature to reduce charging time. This proprietary technique
allows safe and dynamic compensation for the internal impedance of
the battery pack during charge.
SNS
Current-sense input
STAT
Charge status output
BAT
Battery-voltage input
VSS
Ground input
VCC
Supply voltage
CC
Charge control output
TS
Temperature sense
input
COMP
Charge-rate
compensation input
8-Pin PDIP, Narrow SOIC, or TSSOP
PN-205701.eps
SLUS025A – JANUARY 2000 - REVISED MAY 2000
1
bq2057
STAT
Pin Descriptions
SNS
Charge status output
Tri-state indication of charge-in-progress,
charge-complete, and temperature fault.
Current-sense input
Battery current is sensed via the voltage developed on this pin by an external sense resistor.
BAT
VSS
Ground input
CC
Charge-control output
Battery voltage input
Source-follower output that drives an external pass-transistor for current and voltage
regulation.
Voltage sense-input tied directly to the positive side of the battery.
COMP
VCC
VCC supply input
TS
Temperature sense input
Sets the charge-rate compensation level. The
voltage-regulation output may be programmed to vary as a function of the charge
current delivered to the battery.
Input for an external battery-temperature
monitoring circuit. Connecting this input to
Vcc/2 disables this feature.
VCC
VSS
POWER
ON
RESET
BAT
COMP
Charge-rate compensation input
KCOMP
CC
VREG
VCC
CONTROL
BLOCK
SNS
VSNS
LED
STAT
STAT
TS
VTS1, VTS2
2057FBD.eps
Figure 1. Functional Block Diagram
2
bq2057
Sleep Mode
LED = Hi-Z
NO
VCC > VBAT
YES
YES
VBAT ≤ VMIN
YES
Temperature
Check
TS > VTS1
TS < VTS2
NO
Temperature
Fault
LED = Hi-Z
Conditioning
Phase
LED = High
NO
Current
Regulation
Phase
LED = High
Voltage
Regulation
Phase
LED = HIGH
NO
IBAT ≤
IREG
10
YES
Charge
Complete
LED = LOW
VBAT ≤ VRCH
YES
NO
2057OFC.eps
Figure 2. bq2057 Operational Flow Chart
serted. Charge qualification is based on battery temperature and voltage. The bq2057 suspends charge if the
battery temperature is outside the VTS1 to VTS2 range
and suspends charge until the battery temperature is
within the allowed range. The bq2057 also checks the
battery voltage. If the battery voltage is below the
low - v olt a g e t h r es h old V M I N , t h e b q 2 0 5 7 u s e s
trickle-charge to condition the battery. The conditioning
charge rate ICOND is set at 10% of the regulation current. The conditioning current also minimizes heat dis-
Functional Description
Figure 1 is a functional block diagram, Figure 2 an operational flow chart, and Figure 3 a typical charger schematic for the bq2057.
Charge Qualification and Conditioning
When power is applied, the bq2057 starts a charge-cycle
if a battery is already present or when a battery is in-
3
bq2057
RSNS
0.2Ω
DC+
Q1
FZT788B
D2
*
PACK+
C1
0.1µF
R1
1kΩ
VCC
PACKNTC
VCC
7
1
3
6
C2
0.1µF
DC-
bq2057
CC
COMP
SNS
BAT
VCC
TS
VSS
STAT
8
2
RT1
4
TEMP
5
Battery
Pack
D1
RT2
R2
2kΩ
* Optional.
2057ldc.eps
Figure 3. Low-Dropout Single- or Dual-Cell Li-Ion Charger
sipation in the external pass-element during the initial
stage of charge. See Figure 4 for a typical charge-algorithm.
either coke or graphite anodes: 4.1V, 4.2V, 8.2V, and
8.4V.
Other regulation voltages can be achieved by adding a
voltage divider between the positive and negative terminals of the battery pack. The voltage divider presents a
scaled battery pack voltage to BAT input. (See Figures 7
and 8.) The resistor values RB1 and RB2 for the voltage
divider are calculated by the following equation:
Current Regulation
The bq2057 regulates current while the battery-pack
voltage is less than the regulation voltage, VREG. The
bq2057 monitors charge current at the SNS input by the
voltage drop across a sense-resistor, RSNS, in series with
the battery pack. In high-side current sensing configuration (Figure 5), RSNS is placed between the Vcc and SNS
pins, and in low-side sensing (Figure 6) the RSNS is
placed between Vss (battery negative) and SNS (charger
ground) pins.
RB1
VCELL
= N ∗
−1
RB2
VREG
where
N = Number of cells in series
Charge-current feedback, applied through pin SNS, maintains regulation around a threshold of VSNS. The following formula calculates the value of the sense resistor:
RSNS =
VCELL = Desired regulation voltage per cell
Charge Termination and Re-Charge
VSNS
IREG
The bq2057 monitors the charging current during the
voltage-regulation phase. The bq2057 declares a “batterycomplete” condition and terminates charge when the
current tapers off to the charge termination threshold,
VTERM. A new charge cycle begins when the battery voltage falls below the VRCH threshold.
where IREG is the desired charging current.
Voltage Monitoring and Regulation
Voltage regulation feedback is through pin BAT. This input is tied directly to the positive side of the battery
pack. The bq2057 monitors the battery-pack voltage between the BAT and VSS pins. The bq2057 is offered in
four fixed-voltage versions for single- and dual-cells with
4
bq2057
Low-Current
Conditioning
Phase
Current
Regulation
Phase
Voltage Regulation Phase
(Shown with the optional AutoComp feature)
VPACK
VREG
IREG
VBAT
VMIN
IBAT
ICOND = IREG
10
IFULL = IREG
10
GR2057b.eps
Figure 4. bq2057 Typical Charge Algorithm
DC+
DC+
BAT+
RSNS
BAT+
bq2057
1
2
3
4
bq2057
1
2
3
4
DC-
SNS
BAT
VCC
TS
COMP
CC
VSS
STAT
8
7
6
5
SNS
BAT
VCC
TS
COMP
CC
VSS
STAT
8
7
6
5
DC-
BAT-
RSNS
BAT2057HSCS.eps
2057LSCS1.eps
Figure 5. High-Side Current Sensing
Figure 6. Low-Side Current Sensing
5
bq2057
DC+
DC+
BAT+
RSNS
BAT+
RB1
RB1
bq2057
DC-
bq2057
1
2
3
4
DC-
SNS
BAT
VCC
TS
1
2
3
4
COMP
CC
VSS
STAT
RB2
8
7
6
5
SNS
BAT
VCC
TS
COMP
CC
VSS
STAT
8
7
6
5
RB2
BATRSNS
BAT-
2057OVDHSC.eps
2057OVDLSC.eps
Figure 8. Optional Voltage Divider for
Non-Standard Regulation Voltage,
(Low-Side Current Sensing)
Figure 7. Optional Voltage Divider for
Non-Standard Regulation Voltage,
(High-Side Current Sensing)
The resistor values of RT1 and RT2 are calculated by the
following equations:
Temperature Monitoring
The bq2057 continuously monitors temperature by measuring the voltage between the TS and VSS pins. A negative- or a positive-temperature coefficient thermistor
(NTC, PTC) and an external voltage-divider typically develop this voltage. (See Figure 9.) The bq2057 compares
this voltage against its internal VTS1 and VTS2 thresholds
to determine if charging is allowed. (See Figure 10.) The
temperature sensing circuit is immune to any fluctuation
in the VCC, since both the external voltage divider and
the internal thresholds (VTS1 and VTS2) are referenced to
VCC.
For NTC thermistors
RT1 =
RT2 =
( 5 ∗ RTH ∗ RTC)
( 3 ∗ (RTC - RTH ))
(5 ∗
RTH ∗ RTC )
( ( 2 ∗ R ) − ( 7 ∗ R ))
TC
DC+
TH
DC+
RSNS
BAT+
BAT+
bq2057
RT1
DC-
bq2057
1
2
3
4
SNS
BAT
VCC
TS
COMP
CC
VSS
STAT
1
2
3
4
8
7
6
5
SNS
BAT
VCC
TS
COMP 8
CC 7
V
6
SS
STAT 5
RT1
Thermistor
RT2
DCRT2
BAT-
BATRSNS
Thermistor
High-Side Current Sensing
Low-Side Current Sensing
2057TSC.eps
Figure 9. Temperature Sensing Circuits
6
bq2057
Condition
V CC
STAT Pin
Battery conditioning and charging
Charge complete
Temperature fault or sleep mode
Temp Fault
High
Low
High-Z
Automatic Charge-Rate
Compensation
V TS2
Normal Temp Range
To reduce charging time, the bq2057 uses the proprietary AutoComp technique to compensate safely for internal impedance of the battery pack.
V TS1
Figure 11 outlines the major components of a single-cell
Li-Ion battery pack. The Li-Ion battery pack consists of
a cell, protection circuit, fuse, connector, current
sense-resistors, and some wiring. Each of these components contains some resistance. Total impedance of the
battery pack is the sum of the minimum resistances of
all battery-pack components. Using the minimum resistance values reduces the odds for overcompensating.
Overcompensating may activate the safety circuit of the
battery pack.
Temp Fault
V SS
2057TSIT.eps
Figure 10. bq2057 TS Input Thresholds
Compensation is through input pin COMP (Figure 12).
A portion of the current-sense voltage, presented
through this pin, is scaled by a factor of KCOMP and
summed with the regulation threshold, VREG. This process increases the output voltage to compensate for the
battery pack’s internal impedance and for undesired
voltage drops in the circuit.
For PTC thermistors
5 ∗ RTH ∗ RTC
RT1 =
( 3 ∗ (RTH - RTC ))
RT2 =
(5 ∗
RTH ∗ RTC )
( ( 2 ∗ RTH ) − ( 7 ∗ RTC))
where RTC is the cold-temperature resistance and RTH is
the hot-temperature resistance of the thermistor, as
specified by the thermistor manufacturer.
RT1 or RT2 can be omitted if only one temperature setting (Hot or Cold) is required.
R2
Terminal
Wire
BAT+
FUSE
Applying a voltage between the VTS1 and VTS2 thresholds to pin TS disables the temperature-sensing feature.
Cell
Protection
Controller
Low-Power Mode
Terminal
Wire
Wire
BAT-
The bq2057 enters the sleep mode if the VCC falls below
the voltage at the BAT input. This feature prevents
draining the battery pack during the absence of VCC.
Discharge
Wire
Charge
2057SCLIP.eps
Charge Status Display
The bq2057 reports the status of the charger on the
tri-state STAT pin. The three states include “charge in
progress, charge complete, and temperature fault.
Figure 11. Typical Components of a
Single-Cell Li-Ion Pack
7
bq2057
DC+
DC+
BAT+
BAT+
RCOMP2
1
2
3
4
RCOMP1
DCRSNS
bq2057
1 SNS
COMP
2 BAT
CC
3 V
VSS
CC
4
STAT
TS
DC8
7
6
5
bq2057
SNS
COMP
BAT
CC
VSS
VCC
STAT
TS
8
7
6
5
RCOMP1
RSNS
RCOMP2
BATHigh-Side Current Sensing
Low-Side Current Sensing
2057AC.eps
Figure 12. AutoComp Circuits
AutoComp setup requires the following information:
n
Total impedance of battery pack (ZPACK)
n
Maximum charging current (IREG)
where VCOMP is the voltage on COMP pin. This voltage
is referenced to Vcc in high-side current-sensing configuration and to Vss for low-side sensing. VPACK is the
voltage across the battery pack.
The voltage drop VZ across the internal impedance of
the battery pack can then be calculated by
The values of RCOMP1 and RCOMP2 can be calculated using the following equation:
VZ = ZPACK ∗ IREG
VCOMP
RCOMP2
=
VSNS
RCOMP1 + RCOMP2
The required compensation is then calculated using the
following equations:
VCOMP =
VZ
KCOMP
VPACK = VREG + (KCOMP ∗ VCOMP)
8
bq2057
Absolute Maximum Ratings
Symbol
Parameter
Min.
Max.
Units
VCC
VCC relative to VSS
-0.3
+18
V
VT
VCC relative to VSS
-0.3
VCC + 0.3
V
TOPR
Operating ambient temperature
-20
70
°C
TSTG
Storage temperature
-40
125
°C
PD
Power dissipation
300
mW
Notes
DC voltage applied on any pin (excluding VCC)
DC Thresholds (TA=TOPR and VCC = 4.5–15V unless otherwise specified)
Symbol
VREG
Parameter
Rating
Tolerance
Unit
4.10
±1%
V
For bq2057 only; See Note 1,2,3
4.20
±1%
V
For bq2057C only; See Note 1,2,3
8.20
±1%
V
For bq2057T only; See Note 1,2,3
8.40
±1%
V
For bq2057W only; See Note 1,2,3
-110
±10%
mV
VCC = 5V, See Note 4
-115
±10%
mV
VCC = 9V, See Note 4
-115
±15%
mV
All other VCC, See Note 4
3.0
±2%
V
For bq2057 only
3.1
±2%
V
For bq2057C only
6.0
±2%
V
For bq2057T only
6.2
±2%
V
For bq2057W only
2.2
±15%
Voltage regulation reference
VSNS
Current regulation reference
VMIN
Notes
Conditioning voltage reference
KCOMP
AutoComp gain
VTS1
Lower temperature threshold
0.3 ∗ VCC
±3% of VCC
V
Voltage at pin TS, relative to VSS
VTS2
Upper temperature threshold
0.6 ∗ VCC
±3% of VCC
V
Voltage at pin TS, relative to VSS
VRCH
Recharge threshold
VREG - 0.1
±2%
V
Voltage on BAT pin, bq2057 and
bq2057C only
VRCH
Recharge threshold
VREG - 0.2
±2%
V
Voltage on BAT pin, bq2057T
and bq2057W only
VTERM
Charge termination reference
-14
±10mV
mV
Notes:
1.
2.
3.
4.
V/V See Note 1
See Note 4
VCC = VBAT + 0.3V to 15V.
For high-side current-sensing configuration.
For low-side current-sensing, the tolerance is ±1% for TA = 25°C and ±1.2% for TA = TORR.
Voltage at pin SNS, relative to VCC for high-side sensing, and to VSS for low-side sensing,
0°C <= TA <= 50°C
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9
ABCDEFGHIJKLMNOPQRSTUVWXYZ!@#%^&*()_+{}|:"<>?~
bq2057
DC Electrical Characteristics (TA= TOPR, and VCC = 4.5 - 15V unless otherwise specified))
Symbol
Parameter
VCC
Supply voltage
ICC
Operating current
ICCS
Sleep current
Min
Typical
Max
Units
Notes
4.5
-
15
V
-
2
4
mA
Excluding external loads
-
3
6
µA
For bq2057 and bq2057C, See note
-
-
10
µA
For bq2057T and bq2057W, See note
VOL
Output-low voltage
-
0.4
0.6
V
IOL = 10mA; STAT pin
VOH
Output-high voltage
VCC - 0.5
-
-
V
IOH = 5mA; STAT pin
-
-
1
µA
BAT input, VBAT = VREG
-
-
5
µA
SNS, COMP, and TS inputs,
VSNS = VCOMP = VTS = 5V
CC pin, not to exceed PD specification
IIH
Input leakage current
ISNK
Sink current
5
-
40
mA
VOLCC
CC pin output-low
voltage
-
-
1.5
V
At ISNK (minimum)
Note: VBAT ≥ VMIN, VBAT - VCC ≥ 0.8V, +20°C ≤ TA ≤ 70°C.
8-Pin SOIC Narrow (SN)
8-Pin SN (0.150" SOIC)
Inches
10
Millimeters
Dimension
Min.
Max.
Min.
Max.
A
0.060
0.070
1.52
1.78
A1
0.004
0.010
0.10
0.25
B
0.013
0.020
0.33
0.51
C
0.007
0.010
0.18
0.25
D
0.185
0.200
4.70
5.08
E
0.150
0.160
3.81
4.06
e
0.045
0.055
1.14
1.40
H
0.225
0.245
5.72
6.22
L
0.015
0.035
0.38
0.89
bq2057
TS: 8-Pin TSSOP
Inches
Dimension
Min.
Max.
Max.
A
-
0.043
-
1.10
A1
0.002
0.006
0.05
0.15
B
0.007
0.012
0.18
0.30
C
0.004
0.007
0.09
0.18
D
0.114
0.122
2.90
3.10
E
0.169
0.176
4.30
4.48
e
H
0.0256BSC
0.246
0.256
Notes:
1. Controlling dimension: millimeters. Inches shown for reference only.
2 'D' and 'E' do not include mold flash or protrusions. Mold flash or protrusions shall not exceed 0.15mm per side
3 Each lead centerline shall be located within ±0.10mm of its exact true position.
4. Leads shall be coplanar within 0.08mm at the seating plane.
5 Dimension 'B' does not include dambar protrusion. The dambar protrusion(s) shall not cause the lead width
to exceed 'B' maximum by more than 0.08mm.
6 Dimension applies to the flat section of the lead between 0.10mm and 0.25mm from the lead tip.
7 'A1' is defined as the distance from the seating plane to the lowest point of the package body (base plane).
Ordering Information
bq2057
Package Option:
SN = 8-pin narrow SOIC
TS = 8-pin TSSOP
Device:
bq2057 Advanced Li-Ion Linear Charger for One Cell (4.1V)
bq2057C Advanced Li-Ion Linear Charger for One Cell (4.2V)
bq2057T Advanced Li-Ion Linear Charger for Two Cells (8.2V)
bq2057W Advanced Li-Ion Linear Charger for Two Cells (8.4V)
11
Millimeters
Min.
0.65BSC
6.25
6.50
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Copyright © 2000, Texas Instruments Incorporated
12