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Features

Significant reduction in charge

time with AutoComp charge-rate
compensation

Ideal for low-dropout linear regu-

lator design

1-cell, 2-cell, and programmable

multicell versions

Low-cost charger implementation

with minimum number of exter-
nal components

Programmable current limit to

accommodate any battery size

Interface to external trickle

charger for reviving deeply dis-
charged batteries

High-accuracy charge control
Sleep mode for low power con-

sumption

Direct battery voltage sense

w i t h o u t

r e s i s t i v e

d i v i d e r s

(bq2056 and bq2056T)

Small 8-pin SOIC package

General Description

The bq2056 series ICs are low-cost
precision linear charge-control de-
vices for Li-Ion batteries. With a
minimum number of external compo-
nents, the bq2056 is a complete low-
dropout linear charger. The dropout
voltage is typically less than 0.5V
when the bq2056 is used with an ex-
ternal PNP transistor or P-channel
FET. Features include proprietary

automatic charge-rate compensation
(AutoComp) and a trickle-charger in-
terface output for reviving deeply
discharged cells. The bq2056 sup-
ports a single-cell 4.1V pack and the
2056T supports a two-cell 8.2V pack.
The bq2056V may be externally pro-
grammed for supporting other volt-
ages. All versions feature a sleep
mode for low-power applications.

bq2056/T/V

Pin Connections

Low-Dropout Li-Ion Charge-Control ICs with

AutoCompTM Charge-Rate Compensation

PN-205601.eps

8-Pin DIP or Narrow SOIC

INH

TRKL

VSS

COMP

VCC

BAT

SNS

10/98 B

BDbq2056.eps

SNS

BAT

COMP

SNS

TRKL

INH

2.0V

REG

100mV

Functional Block Diagram

Pin Names

INH

Charge-inhibit input

TRKL

Trickle-charge
interface output

Ground

COMP

Charge-rate
compensation input

SNS

Current sense input

BAT

Battery voltage input

Charge control
output

Supply input

Pin Descriptions:

INH

Charge-inhibit input

When input to this pin is high, the bq2056
suspends the charge in progress and places
the device in sleep mode. When input is low,
the bq2056 resumes operation.

TRKL

Trickle-charge interface output

This output is driven low if the battery volt-
age is less than an internal threshold level
and INH is low. This open-drain output can
enable an external trickle charger to revive a
deeply discharged battery.

Ground

COMP

Charge-rate compensation input

This input is used to set 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. This feature, called AutoComp,
provides compensation for internal cell im-
pedance and voltage drops in protection
circuitry and therefore may be used to
safely reduce charging time. Connecting
this pin to V

disables the AutoComp fea-

ture.

SNS

Current sense input

Battery current is sensed via the voltage
developed on this pin by an external sense-
resistor, connected in series with the nega-
tive terminal of the battery pack.

BAT

Battery voltage input

This is the battery voltage sense input. It is
tied directly to the positive side of the bat-
tery pack on bq2056 and bq2056T versions.
A simple resistive divider is required to
generate this input for bq2056V.

Charge-control output

CC is an open-collector output that is used
to control the charging current to the bat-
tery.

supply input

bq2056/T/V

Functional Description

The bq2056 supports a precision current- and voltage-
limited charging system for Li-Ion batteries. The no-load
voltage regulation references (V

REG

) for the bq2056 and

bq2056T are maintained at 4.1V and 8.2V, respectively.
The bq2056V provides variable regulation to accommo-
date a wide range of charge voltages and may be used to
meet tighter tolerance requirements through external
trimming. The functional block diagram for the bq2056
is on the first page of this data sheet, and Figure 1 illus-
trates a typical application.

Charge Algorithm

The bq2056 completes the charge cycle in two phases. A
constant current phase replenishes approximately 70%
of battery capacity, while an accurate voltage regulation
phase completes the charge.

Figure 2 shows a typical charge algorithm for bq2056,
including charge qualification, current regulation, and
voltage regulation phases.

Charge Qualification

During charge qualification the bq2056 detects a low
battery and reports this status on pin TRKL. Detection

is accomplished by comparing pin BAT voltage to the in-
ternal threshold V

MIN

. While pin BAT voltage is less

than V

MIN

and pin INH is low, the open-drain output

TRKL is driven low and the voltage/current regulator is
disabled (CC=high-Z). In the bq2056V, low-voltage de-
tection occurs when the voltage on pin BAT is less than
or equal to V

MIND

. As shown in Figure 1, TRKL enables

an external trickle-charge circuit to bring the battery
voltage up to V

MIN

or V

MIND.

Current Regulation

The bq2056 provides current regulation while the pack
voltage is below the voltage limit. Charge-current feed-
back, applied through pin SNS, maintains regulation
around a threshold of V

SNS

. The following formula calcu-

lates the value of the sense-resistor connected in series
with the negative terminal of the battery pack (Figure 3):

SNS

= 0.1/ I

MAX

where I

MAX

is the maximum charging current. I

MAX

should not exceed 1A.

An external PNP or power P-FET may be used as the se-
ries pass element with control provided through output
pin CC.

bq2056sc.eps

INH

TRKL

bq2056

COMP

VCC

BAT

SNS

BAT+

BAT-

R6
0.3

C1
10 F
10V

0.1 F

R2 1K

R1
1K

DC+

DC-

R5
2K

R5
2.7K

1N5817

2N3906

2TX788B

5 VDC

4.7K

Figure 1. Low-Dropout Single-Cell Li-Ion Charger

bq2056/T/V

Voltage Regulation

Voltage regulation feedback is through pin BAT. This pin
is connected directly to the pack in the bq2056 and
bq2056T. This voltage is compared with the voltage
regulation reference, V

REG

. In the bq2056V, a resistive

divider may be used to generate this input (Figure 4). In
this case, the voltage presented on pin BAT is compared
with the internal reference voltage V

REF

. The resistor

values R

and R

(Figure 4) are calculated based on

the following equation:

N V

CELL

REF

where

= Number of cells in series

CELL

= Manufacturer-specified charging voltage

Automatic Charge-Rate Compensation
(AutoComp) Feature

To reduce charging time, the bq2056 series uses the pro-
prietary AutoComp technique to compensate safely for
internal impedance of battery and any voltage drops in
the protection circuitry. This maximizes battery's capac-
ity while reducing charging time. Compensation is
through input pin COMP (Figure 5). A portion of the
current-sense voltage, presented through this pin, is
scaled by a factor of K

COMP

and summed with the regu-

lation reference, V

REG

. This process increases the output

voltage to compensate for the battery's internal imped-
ance and undesired voltage drops in the circuit.

For bq2056 and bq2056T, the voltage across the battery
pack, V

PAK

, is

PAK

= V

REG

+ (K

COMP

voltage on pin COMP)

For bq2056V, the compensation voltage is added to the
product of the internal voltage reference, V

REF

, and the

gain, KDIV, of the external resistive divider between the
battery pack and BAT input, (Figure 4).

PAK

= (V

REF

DIV

) + (K

COMP

voltage on pin COMP)

Sleep Mode

The charge function may be disabled through pin INH.
When INH is driven high, internal current consumption
is reduced, and pins CC and TRKL assumes a high-
impedance output state.

bq2056/T/V

2056chg.eps

VREG

IMAX

VMIN

External

Trickle Charge

Enabled

Current

Regulation

Current

Voltage Regulation

Voltage

AutoCompTM

Phase

Current

Voltage

Figure 2. bq2056 Charge Algorithm

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