1
Features
➤Ideal for single- and dual-cell Li-Ion
packs with coke or graphite anodes
➤Dropout voltage as low as 0.3V
➤AutoComp™ dynamic compensa-
tion of battery pack’s internal im-
pedance
➤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 regula-
tion accuracy
➤Charge status output for LED or
host processor interface
➤Automatic battery-recharge feature
➤Charge termination by minimum
current
➤Low-power sleep mode
➤Packaging: 8-pin SOIC, 8-pin
TSSOP
General Description
The BENCHMARQ bq2057 series
advanced Li-Ion linear charge-man-
agement ICs are designed for
cost-sensitive and compact portable
electronics. They combine high-accu-
racy current and voltage regulation,
battery conditioning, temperature
monitoring, charge termination,
charge-status indication, and
AutoComp charge-rate compen-
sation in a single 8-pin IC.
The bq2057 continuously measures
battery temperature using an exter-
nal 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 cur-
rent, and constant voltage. If the
battery voltage is below the
low-voltage threshold VMIN, 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.
After conditioning, the bq2057 ap-
plies a constant current to the bat-
tery. An external sense-resistor sets
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 con-
stant-voltage phase. The accuracy of
the voltage regulation is better than
±1% over the operating-temperature
and supply-voltage ranges. For sin-
gle and dual cells with either coke
or graphite anodes, the bq2057 is of-
fered in four fixed-voltage versions:
4.1V, 4.2V, 8.2V, and 8.4V. Charge
stops when the current tapers to the
charge termination threshold,
VTERM. The bq2057 automatically
restarts the charge if the battery
voltage falls below the VRCH thresh-
old.
The designer also may use the
AutoComp feature to reduce charg-
ing time. This proprietary technique
allows safe and dynamic compensa-
tion for the internal impedance of
the battery pack during charge.
bq2057
Pin Connections
Advanced Li-Ion Linear Charge
Management IC
1
PN-205701.eps
8-Pin PDIP, Narrow SOIC, or TSSOP
2
3
4
8
7
6
5
SNS
BAT
V
CC
TS
COMP
CC
V
SS
STAT
Pin Names
SNS Current-sense input
BAT Battery-voltage input
VCC Supply voltage
TS Temperature sense
input
STAT Charge status output
VSS Ground input
CC Charge control output
COMP Charge-rate
compensation input
SLUS025A – JANUARY 2000 - REVISED MAY 2000
Pin Descriptions
SNS Current-sense input
Battery current is sensed via the voltage de-
veloped on this pin by an external sense re-
sistor.
BAT Battery voltage input
Voltage sense-input tied directly to the posi-
tive side of the battery.
VCC VCC supply input
TS Temperature sense input
Input for an external battery-temperature
monitoring circuit. Connecting this input to
Vcc/2 disables this feature.
STAT Charge status output
Tri-state indication of charge-in-progress,
charge-complete, and temperature fault.
VSS Ground input
CC Charge-control output
Source-follower output that drives an exter-
nal pass-transistor for current and voltage
regulation.
COMP Charge-rate compensation input
Sets the charge-rate compensation level. The
voltage-regulation output may be pro-
grammed to vary as a function of the charge
current delivered to the battery.
2
bq2057
VCC
CC
CONTROL
BLOCK
VREG
VSS VCC
COMP
BAT
POWER
RESET
ON
SNS
2057FBD.eps
TS
VTS1, VTS2
VSNS LED
STAT STAT
KCOMP
Figure 1. Functional Block Diagram
Functional Description
Figure 1 is a functional block diagram, Figure 2 an oper-
ational flow chart, and Figure 3 a typical charger sche-
matic 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-
serted. Charge qualification is based on battery temper-
ature 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-voltage threshold VMIN, the bq2057 uses
trickle-charge to condition the battery. The conditioning
charge rate ICOND is set at 10% of the regulation cur-
rent. The conditioning current also minimizes heat dis-
3
bq2057
V
CC
> V
BAT
Temperature
Check
TS > V
TS1
TS < V
TS2
V
BAT
≤ V
MIN
I
BAT
≤ V
BAT
≤ V
RCH
Sleep Mode
LED = Hi-Z NO
YES
YES
NO
NO
NO
2057OFC.eps
NO
YES
YES YES
Current
Regulation
Phase
LED = High
Voltage
Regulation
Phase
LED = HIGH
Charge
Complete
LED = LOW
Temperature
Fault
LED = Hi-Z
Conditioning
Phase
LED = High
I
REG
10
Figure 2. bq2057 Operational Flow Chart
sipation in the external pass-element during the initial
stage of charge. See Figure 4 for a typical charge-algo-
rithm.
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 configura-
tion (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.
Charge-current feedback, applied through pin SNS, main-
tains regulation around a threshold of VSNS. The follow-
ing formula calculates the value of the sense resistor:
RSNS =V
I
SNS
REG
where IREG is the desired charging current.
Voltage Monitoring and Regulation
Voltage regulation feedback is through pin BAT. This in-
put is tied directly to the positive side of the battery
pack. The bq2057 monitors the battery-pack voltage be-
tween the BAT and VSS pins. The bq2057 is offered in
four fixed-voltage versions for single- and dual-cells with
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 termi-
nals 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:
R
RNV
V
B1
B2
CELL
REG
=∗
−1
where
N = Number of cells in series
VCELL = Desired regulation voltage per cell
Charge Termination and Re-Charge
The bq2057 monitors the charging current during the
voltage-regulation phase. The bq2057 declares a “battery-
complete” condition and terminates charge when the
current tapers off to the charge termination threshold,
VTERM. A new charge cycle begins when the battery volt-
age falls below the VRCH threshold.
4
bq2057
2057ldc.eps
PACK+
Q1
FZT788B D2
bq2057
CC
Battery
Pack
V
CC
V
CC
R
T1
R
T2
NTC
C1
0.1µF
C2
0.1µF
R2
2kΩ
R
SNS
0.2Ω
R1
1kΩ
D1
SNS
VCC
VSS
COMP
BAT
TS
STAT
DC+
DC-
TEMP
PACK-
78
2
4
5
1
3
6
Figure 3. Low-Dropout Single- or Dual-Cell Li-Ion Charger
*
* Optional.
5
bq2057
BAT+
BAT-
DC+
DC-
RSNS
STAT 5
VSS 6
CC 7
COMP 8
SNS
1
BAT
2
VCC
3
TS
4
bq2057
2057HSCS.eps
Figure 5. High-Side Current Sensing
GR2057b.eps
V
BAT
I
BAT
V
PACK
V
REG
V
MIN
I
REG
Low-Current
Conditioning
Phase
Current
Regulation
Phase
Voltage Regulation Phase
(Shown with the optional AutoComp feature)
I
REG
10
I
REG
10
I
COND
= I
FULL
=
Figure 4. bq2057 Typical Charge Algorithm
STAT 5
V
SS
6
CC 7
COMP 8
SNS
1
BAT
2
V
CC
3
TS
4
bq2057
BAT+
BAT-
DC+
R
SNS
2057LSCS1.eps
DC-
Figure 6. Low-Side Current Sensing
Temperature Monitoring
The bq2057 continuously monitors temperature by mea-
suring the voltage between the TS and VSS pins. A nega-
tive- or a positive-temperature coefficient thermistor
(NTC, PTC) and an external voltage-divider typically de-
velop 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.
The resistor values of RT1 and RT2 are calculated by the
following equations:
For NTC thermistors
()
()
()
R= 5R R
3R-R
T1
TH TC
TC TH
∗∗
∗
()
()()
()
R= 5R R
2R 7R
T2
TH TC
TC TH
∗∗
∗−∗
6
bq2057
BAT+
BAT-
2057OVDHSC.eps
R
SNS
R
B1
R
B2
DC+
STAT 5
V
SS
6
CC 7
COMP 8
SNS
1
BAT
2
V
CC
3
TS
4
bq2057
DC-
Figure 7. Optional Voltage Divider for
Non-Standard Regulation Voltage,
(High-Side Current Sensing)
BAT+
BAT-
2057OVDLSC.eps
R
SNS
R
B1
R
B2
DC+
STAT 5
V
SS
6
CC 7
COMP 8
SNS
1
BAT
2
V
CC
3
TS
4
bq2057
DC-
Figure 8. Optional Voltage Divider for
Non-Standard Regulation Voltage,
(Low-Side Current Sensing)
BAT+
BAT-
Thermistor
DC+ DC+
R
SNS
RT2
RT1
STAT 5
V
SS
6
CC 7
COMP 8
SNS
1
BAT
2
V
CC
3
TS
4
bq2057
High-Side Current Sensing Low-Side Current Sensing
2057TSC.eps
STAT
5
V
SS
6
CC
7
COMP
8
SNS
1
BAT
2
V
CC
3
TS
4
bq2057
BAT+
BAT-
R
SNS
R
T2
R
T1
Thermistor
DC-
DC-
Figure 9. Temperature Sensing Circuits
For PTC thermistors
()
()
R= 5R R
3R-R
T1
TH TC
TH TC
∗∗
∗
()
()()
()
R= 5R R
2R 7R
T2
TH TC
TH TC
∗∗
∗−∗
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 set-
ting (Hot or Cold) is required.
Applying a voltage between the VTS1 and VTS2 thresh-
olds to pin TS disables the temperature-sensing feature.
Low-Power Mode
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.
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.
Condition STAT Pin
Battery conditioning and charging High
Charge complete Low
Temperature fault or sleep mode High-Z
Automatic Charge-Rate
Compensation
To reduce charging time, the bq2057 uses the propri-
etary AutoComp technique to compensate safely for in-
ternal impedance of the battery pack.
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 compo-
nents contains some resistance. Total impedance of the
battery pack is the sum of the minimum resistances of
all battery-pack components. Using the minimum resis-
tance values reduces the odds for overcompensating.
Overcompensating may activate the safety circuit of the
battery pack.
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 pro-
cess increases the output voltage to compensate for the
battery pack’s internal impedance and for undesired
voltage drops in the circuit.
7
bq2057
V
CC
V
TS2
V
TS1
Temp Fault
2057TSIT.eps
Temp Fault
Normal Temp Range
V
SS
Figure 10. bq2057 TS Input Thresholds
BAT-
BAT+
Wire
Terminal
Terminal
Discharge Charge
2057SCLIP.eps
Protection
Controller
R2
FUSE
Wire
Cell
WireWire
Figure 11. Typical Components of a
Single-Cell Li-Ion Pack
AutoComp setup requires the following information:
nTotal impedance of battery pack (ZPACK)
nMaximum charging current (IREG)
The voltage drop VZ across the internal impedance of
the battery pack can then be calculated by
VZ= ZPACK ∗IREG
The required compensation is then calculated using the
following equations:
V=
V
K
COMP
Z
COMP
VPACK = VREG + (KCOMP ∗VCOMP)
where VCOMP is the voltage on COMP pin. This voltage
is referenced to Vcc in high-side current-sensing config-
uration and to Vss for low-side sensing. VPACK is the
voltage across the battery pack.
The values of RCOMP1 and RCOMP2 can be calculated us-
ing the following equation:
V
V
R
R+R
COMP
SNS
COMP2
COMP1 COMP2
=
8
bq2057
R
COMP1
R
SNS
R
COMP2
DC+
High-Side Current Sensing
STAT 5
V
SS
6
CC 7
COMP 8
SNS
1
BAT
2
V
CC
3
TS
4
bq2057
BAT+ BAT+
BAT-
R
COMP1
STAT 5
V
SS
6
CC 7
COMP 8
SNS
1
BAT
2
V
CC
3
TS
4
bq2057
DC+
R
SNS
Low-Side Current Sensing
2057AC.eps
R
COMP2
DC-
DC-
Figure 12. AutoComp Circuits
9
bq2057
DC Thresholds (TA=TOPR and VCC = 4.5–15V unless otherwise specified)
Symbol Parameter Rating Tolerance Unit Notes
VREG Voltage regulation reference
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
VSNS Current regulation reference
-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
VMIN Conditioning voltage reference
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
KCOMP AutoComp gain 2.2 ±15% V/V See Note 1
VTS1 Lower temperature threshold 0.3 ∗VCC ±3% of VCC VVoltage at pin TS, relative to VSS
VTS2 Upper temperature threshold 0.6 ∗VCC ±3% of VCC VVoltage 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 See Note 4
Notes: 1. VCC = VBAT + 0.3V to 15V.
2. For high-side current-sensing configuration.
3. For low-side current-sensing, the tolerance is ±1% for TA = 25°C and ±1.2% for TA = TORR.
Absolute Maximum Ratings
Symbol Parameter Min. Max. Units Notes
VCC VCC relative to VSS -0.3 +18 V
VTVCC relative to VSS -0.3 VCC + 0.3 VDC voltage applied on any pin (ex-
cluding VCC)
TOPR Operating ambient temperature -20 70 °C
TSTG Storage temperature -40 125 °C
PDPower dissipation 300 mW
4. Voltage at pin SNS, relative to VCC for high-side sensing, and to VSS for low-side sensing,
0°C <= TA <= 50°C
abcdefghijklmnopqrstuvwxyz1234567890-=`[]\;',./
ABCDEFGHIJKLMNOPQRSTUVWXYZ!@#%^&*()_+{}|:"<>?~
10
bq2057
DC Electrical Characteristics (TA= TOPR, and VCC = 4.5 - 15V unless otherwise specified))
Symbol Parameter Min Typical Max Units Notes
VCC Supply voltage 4.5 - 15 V
ICC Operating current - 2 4 mA Excluding external loads
ICCS Sleep current
-36
µAFor bq2057 and bq2057C, See note
--10
µAFor 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
IIH Input leakage current
--1
µABAT input, VBAT = VREG
--5
µASNS, COMP, and TS inputs,
VSNS = VCOMP = VTS = 5V
ISNK Sink current 5 - 40 mA CC pin, not to exceed PDspecification
VOLCC CC pin output-low
voltage - - 1.5 V At ISNK (minimum)
Note: VBAT ≥VMIN,V
BAT - VCC ≥0.8V, +20°C≤TA≤70°C.
8-Pin SOIC Narrow (SN)
8-Pin SN (0.150" SOIC)
Dimension
Inches Millimeters
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
11
bq2057
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).
Dimension Inches Millimeters
Min. Max. Min. 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 0.0256BSC 0.65BSC
H 0.246 0.256 6.25 6.50
TS: 8-Pin TSSOP
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)
12
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