Pin Descriptions

DC

DC supply input

This input is used to charge the rechargeable

alkaline cells and power the bq2902 during

charge. To charge the batteries, this input

should be connected to a current-source lim-

ited to 300 mA. If the DC input current is

greater than 300mA, the power dissipation

limits of the package may be exceeded. The

DC input should also be capable of supplying

a minimum of 3.3V and should not exceed

5.5V.

CHG

Charge status

This open-drain output is used to signify the

battery charging status and is valid only

when DC is applied.

End-of-discharge select input

This three-level input selects the desired

end-of-discharge cut-off voltage for the

Battery 1 positive input

This input connects to the positive terminal

3). This pin also provides power to the bq2902

when DC is not present.

Battery 1 negative input

This input connects to the negative terminal

Battery 2 negative input/IC ground

This input connects to the negative terminal

LRTN

Load return

This open-drain pull-down output is typi-

cally used as a low-side switch. High-side

load switching is also possible with the addi-

tion of an external P-FET.

Functional Description

Figure 1 is a block diagram outlining the major compo-

nents of the bq2902.

Figure 2 illustrates the charge control and display

status during a bq2902 cycle. Table 1 outlines the vari-

2

bq2902

BD290201.eps

Control/Status

Logic

DC

VSEL

CHG

BAT1P

BAT1N

LRTN

VSS

VSS

3

2

5

6

7

4

1

8

Figure 1. Functional Block Diagram