Functional Description

Figure 1 is a block diagram of the bq4847. The bq4847 is

functionally equivalent to the bq4845 except that the bat-

tery (20, 24) and crystal (2, 3) pins are not accessible. The

pins are connected internally to a coin cell and quartz

crystal. The coin cell provides 130mAh of capacity. It is in-

tion is broken, and the backup cell provides power to

clock keeps time to within one minute per month at

room temperature. For a complete description of fea-

tures, operating conditions, electrical characteristics,

bus timing, and pin descriptions, see the bq4845 data

sheet. Valid part types for ordering are bq4847MT (5%)

and bq4847YMT (10%).

Figure 2 illustrates the address map for the bq4847. Ta-

ble 1 is a map of the bq4847 registers, and Table 2 de-

scribes the register bits.

2

Figure 1. Block Diagram

CS

OE

WE

Mode

DQ

Power

XX

Deselect

High Z

Standby

Write

Active

Read

Active

Read

High Z

Active

XXX

Deselect

High Z

CMOS standby

XXX

Deselect

High Z

Battery-backup mode

Truth Table

bq4847/bq4847Y

Sept. 1996