TEXAS INSTRUMENTS bq2057, bq2057C, bq2057W, bq2057T Technical data

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bq2057/C/W/T

Advanced Li-Ion Linear Charge

Management IC

Features

Ideal forsingle- and dual-cell Li-Ion
packs with coke or graphite anodes

0.3V dropout voltage
AutoComp™ dynamic compensa

tion ofbattery 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 ofcharge

Better than
tion accuracy

Charge status output for LED or
host processor i nterface

Automatic battery-recharge feature
Charge termination by minimum

current
Low-power sleep mode
Packaging: 8-pin SOIC, 8-pin

TSSOP

±

1% voltage regula-

General Description

The BENCHMARQ bq2057 series
advanced Li-Ion linear charge­management ICs are designed for
cost-sensitive and compact portable
electronics. They combine high-

­accuracy current and voltage

­regulation, battery conditioning,

temperature monitoring, charge
termination, charge-status indi­cation, and AutoComp charge-rate
compensation in a single 8-pin IC.

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 th e battery in three
phases: conditioning, constant cur­rent, and constant voltage. If the bat­tery voltage is below the low-voltage
threshold V
trickle-charges to condition the bat­tery. The conditioning charge rate is
set at approximately 10% of the reg­ulation current. The conditioning
current also minimizes heat dissipa­tion in t he external pass-element
during the initial stage ofcharge.

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

, th e bq2057

MIN

low or t h e high side of th e battery
without additional components. The
constant-current phase continues
until the battery reaches th 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
charge termination threshold,
V

. The bq2057 automatically re-

TERM

starts the charge if the battery volt­age falls belowthe V

The designer also may use the
AutoComp feature to reduce charg­ing time. This proprietary technique
allows safe and dynamic compensa­tion for t h e internal impedance of
the battery pack during charge.

Available Options

Part Number

-

-

bq2057 4.1V
bq2057C 4.2V
bq2057T 8.2V

bq2057W 8.4V

threshold.

RCH

Charge

Regulation

Voltage

-

-

-

Pin Connections

SLUS025B–JANUARY2000–REVISED JUNE 2000

Pin Names

SNS Current-sense input
BAT Battery-voltage input
V
TS Temperature sense

CC

Supply voltage

input

1

STAT Charge status output
V
CC Charge control output
COMP Charge-rate

Ground input

SS

compensation input

bq2057

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 ofthe battery.

V

CC

TS Temperaturesenseinput

VCCsupplyinput

Input for an external battery-temperature
monitoring circuit. Connecting this input to
Vcc/2 disables th i s feature.

BAT

STAT Charge status output

Tri-state indication of charge-in-progress,
charge-complete, andtemperature fault.

-

V

SS

-

Ground input

CC Charge-control output

Source-follower output that drives a n 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 ofthe charge
current delivered to the battery.

V

SS

V

CC

POWER

ON

RESET

CC

COMP

SNS

TS

K

COMP

V

REG

CONTROL

V

SNS

V

, V

TS1

TS2

Figure 1. Functional Block Diagram

2

BLOCK

LED

STAT

VCC

STAT

2057FBD.eps

bq2057

Sleep Mode

LED = Hi-Z

V

≤ V

BAT

MIN

NO

Current

Regulation

Phase

LED = High

Voltage

Regulation

Phase

LED = HIGH

NO

YES

YES

NO

VCC > V

BAT

YES

Temperature

Check

TS > V

TS1

TS < V

TS2

Conditioning

Phase

LED = High

I

REG

I

≤ V

BAT

10

YES

NO

Temperature

Fault

LED = Hi-Z

Charge

Complete

LED = LOW

YES

≤ V

BAT

RCH

2057OFC.eps

Figure 2. Operational Flow Chart

Functional Description

Figure 1 is a functional block diagram, Figure 2 a n oper
ational flow chart, an d Figure 3 a typical charger sche
matic forthe 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

NO

serted. Charge qualification is based on battery temper
ature and voltage. The bq2057 suspends charge if the
battery temperature is outside the V

­and suspends charge until the battery temperature is

­within th e allowed range. The bq2057 also checks the

TS1

to V

battery voltage. If the battery voltage is below the
low-voltage threshold V
trickle-charge to condition the battery. The conditioning
charge rate I

-

regulation current. The conditioning current also mini

is set at approximately 10% of the

COND

, th e bq2057 uses

MIN

3

TS2

-

range

-

bq2057

R

DC+

DC-

SNS

0.2Ω

0.1µF

Q1

FZT788B

R1
1kΩ

78

CC

1

SNS

3

V

CC

6

V

C2

SS

bq2057

COMP

BAT

STAT

D2

V

CC

V

CC

2

4

TS

5

D1

R2
2kΩ

R

T1

R

T2

C1

0.1µF

PACK+

PACK-

TEMP

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

Battery

2057ldc.eps

NTC

Pack

mizes heat dissipation in the external pass-element dur­ing t he initial stage ofcharge. See Figure 4 for a typical
charge-algorithm.

Current Regulation

The bq2057 regulates current while the battery-pack
voltage i s less than the regulation voltage, V
bq2057 monitors charge current a t the SNSinput by the
voltage drop across a sense-resistor, R
the battery pack. I n high-side current sensing configura
tion (Figure 5), R
pins, and in low-side sensing (Figure 6) the R

is placed between the Vcc and SNS

SNS

, in series with

SNS

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

Charge-current feedback, applied through pin SNS,
maintains regulation around a threshold ofV
lowing formula calculates the value ofthe sense resistor:

V

SNS

SNS

=

REG

I

where I

R

is the desired charging current.

REG

SNS

. The

REG

SNS

. The fol

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 t he battery-pack voltage be
tween the BAT and V
four fixed-voltage versions for single- and dual-cells with

pins. The bq2057 is offered in

SS

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 th e battery pack. The voltage divider presents a
scaled battery pack voltage to BAT input. (See Figures 7
and 8.) The resistor values R
divider ar e calculated bythe following equation:

R

B1

-

is

=∗

B2

R






and RB2for the voltage

B1

V

CELL



N



−

1

REG

V



where

N=Number ofcellsin series

-

V

= Desired regulation voltage pe r cell

CELL

Charge Terminationand Re-Charge

The bq2057 monitors the charging current during the
voltage-regulation phase. The bq2057 declares a “battery­complete” condition a nd terminates charge when the
current tapers off to the charge termination threshold,
V

. A new charge cycle begins when the battery volt

TERM

age falls below the

-

-

VRCH

threshold.

-

4