Functional Description

The bq2056 supports a precision current- and voltage-

limited charging system for Li-Ion batteries. The no-load

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-

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

an external trickle-charge circuit to bring the battery

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

lates the value of the sense-resistor connected in series

with the negative terminal of the battery pack (Figure 3):

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.

3

bq2056sc.eps

INH

TRKL

bq2056

VS

COMP

VCC

CC

BAT

SNS

1

2

3

4

8

7

6

5

BAT+

BAT-

R6

0.3

C1

10 F

10V

C2

0.1 F

R2 1K

R1

1K

DC+

DC-

R5

2K

R5

2.7K

D1

1N5817

Q1

2N3906

2TX788B

Q2

5 VDC

R3

4.7K

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

bq2056/T/V