TEXAS INSTRUMENTS bq2056, bq2056T, bq2056V Technical data

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bq2056/T/V

Low-Dropout Li-Ion Charge-Control ICs with

AutoComp™ Charge-Rate Compensation

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 discharged batteries

➤ High-accuracy charge control

➤ Sleep mode for low power con-

sumption

➤ Direct battery voltage sense

without resistive dividers (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

Functional Block Diagram

SNS

BAT

COMP

SNS

INH

COMP

REG

100mV

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.

2.0V

BDbq2056.eps

TRKL

Pin Connections

INH

TRKL

COMP

8-Pin DIP or Narrow SOIC

PN-205601.eps

BAT

SNS

Pin Names

INH Charge-inhibit input

TRKL Trickle-charge

COMP Charge-rate

interface output

Ground

compensation input

SNS Current sense input

BAT Battery voltage input

CC Charge control

output

Supply input

10/98 B

bq2056/T/V

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.

COMP Charge-rate compensation input

Ground

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 impedance and voltage drops in protection circuitry and therefore may be used to safely reduce charging time. Connecting this pin to V ture.

disables the AutoComp fea-

SNS Current sense input

Battery current is sensed via the voltage developed on this pin by an external senseresistor, 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

CC Charge-control output

tery pack on bq2056 and bq2056T versions. A simple resistive divider is required to generate this input for bq2056V.

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

VCCsupply input

bq2056/T/V

5 VDC

DC+

DC-

1N5817

2N3906

2.7K

INH

TRKL

COMP

R1 1K

bq2056

R2 1K

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

Functional Description

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

) for the bq2056 and

REG

4.7K 2TX788B

0.3

R5 2K

C1 10 F 10V

BAT+

BAT-

bq2056sc.eps

0.1 F

VCC

BAT

SNS

is accomplished by comparing pin BAT voltage to the internal threshold V than V

and pin INH is low, the open-drain output

MIN

. While pin BAT voltage is less

MIN

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 an external trickle-charge circuit to bring the battery

voltage up to V

. As shown in Figure 1, TRKL enables

MIND

or V

MIN

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

where I

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.

. The following formula calcu

SNS

= 0.1/ I

SNS

MAX

bq2056/T/V

External

Trickle Charge

Enabled

MAX

Current

Regulation

Figure 2. bq2056 Charge Algorithm

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 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 values R

and RB2(Figure 4) are calculated based on

the following equation:

. In the bq2056V, a resistive

REG

RRNV

CELL

∗

REF

−

. The resistor

REF

AutoComp™

Phase

REG

MIN

Voltage

Voltage Regulation

Current

2056chg.eps

voltage to compensate for the battery’s internal impedance and undesired voltage drops in the circuit.

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

,is

PAK

PAK=VREG

+ (K

∗ voltage on pin COMP)

COMP

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

, and the

REF

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

= (V

∗ K

PAK

REF

DIV

) + (K

∗ voltage on pin COMP)

COMP

where

N = Number of cells in series

= Manufacturer-specified charging voltage

CELL

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 lation reference, V

REG

and summed with the regu

COMP

. This process increases the output

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 highimpedance output state.

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