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Features

Ideal for single- and dual-cell Li-Ion

packs with coke or graphite anodes

Dropout voltage as low as 0.3V
AutoCompTM dynamic compensa-

tion of battery pack's internal im-
pedance

Optional temperature-monitoring

before and during charge

Integrated voltage and current

regulation with programmable
ch a r g e - c u r r e n t a n d h i g h - o r
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,
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 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
b a t t e r y t e m p e r a t u r e i s w i t h i n
user-defined thresholds. The bq2057
then charges the battery in three
phases: conditioning, constant cur-
rent, and constant voltage. If the
b a t t e r y v o l t a g e i s b e l o w t h e
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.

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
u n t i l t h e b a t t e r y r e a c h e s t h e
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
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 ,
V

TERM

. The bq2057 automatically

restarts the charge if the battery
voltage falls below the V

RCH

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

PN-205701.eps

8-Pin PDIP, Narrow SOIC, or TSSOP

SNS

BAT

COMP

STAT

Pin Names

SNS

Current-sense input

BAT

Battery-voltage input

Supply voltage

Temperature sense
input

STAT

Charge status output

Ground input

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.

supply input

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.

Ground input

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.

bq2057

VCC

CONTROL

BLOCK

REG

COMP

BAT

POWER

RESET

SNS

2057FBD.eps

TS1

, V

TS2

SNS

LED

STAT

COMP

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 V

TS1

to V

TS2

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
l o w - v o l t a g e t h r e s h o l d 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 I

COND

is set at 10% of the regulation cur-

rent. The conditioning current also minimizes heat dis-

bq2057

> V

BAT

Temperature

Check

TS > V

TS1

TS < V

TS2

BAT

MIN

BAT

RCH

Sleep Mode

LED = Hi-Z

YES

2057OFC.eps

YES

Current

Regulation

Phase

LED = High

Voltage

Regulation

Phase

LED = HIGH

Charge

Complete

LED = LOW

Temperature

Fault

LED = Hi-Z

Conditioning

Phase

LED = High

REG

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, V

REG

. The

bq2057 monitors charge current at the SNS input by the
voltage drop across a sense-resistor, R

SNS

, in series with

the battery pack. In high-side current sensing configura-
tion (Figure 5), R

SNS

is placed between the Vcc and SNS

pins, and in low-side sensing (Figure 6) the R

SNS

placed between Vss (battery negative) and SNS (charger
ground) pins.

Charge-current feedback, applied through pin SNS, main-
tains regulation around a threshold of V

SNS

. The follow-

ing formula calculates the value of the sense resistor:

SNS

REG

where I

REG

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 V

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 R

and R

for the voltage

divider are calculated by the following equation:

CELL

REG

- 1

where

N = Number of cells in series

CELL

= 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,
V

TERM

. A new charge cycle begins when the battery volt-

age falls below the

VRCH

threshold.

bq2057

2057ldc.eps

PACK+

FZT788B

bq2057

Battery

Pack

NTC

C1
0.1

µF

0.1

µF

R2
2k

SNS

0.2

R1
1k

SNS

VCC

VSS

COMP

BAT

STAT

DC+

DC-

TEMP

PACK-

Figure 3. Low-Dropout Single- or Dual-Cell Li-Ion Charger

* Optional.

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