BQ4847 Datasheet, PDF (2/5 Pages) Texas Instruments – RTC Module With CPU Supervisor

bq4847/bq4847Y
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-
ternally isolated from VOUT and CEOUT until the initial
application of VCC. Once VCC rises above VPFD, this isola-
tion is broken, and the backup cell provides power to
VOUT and CEOUT for the external SRAM. The real-time
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.
Truth Table
VCC
CS
< VCC (max.)
VIH
VIL
> VCC (min.)
VIL
VIL
< VPFD (min.) > VSO X
≤ VSO
X
Figure 1. Block Diagram
OE
WE
CEOUT VOUT
Mode
DQ
Power
X
X
CEIN VOUT1 Deselect High Z
Standby
X
VIL
CEIN V_OUT1
Write
DIN
Active
VIL
VIH
CEIN V_OUT1
Read
DOUT
Active
VIH
VIH
CEIN V_OUT1
Read High Z
Active
X
X
VOH VOUT1 Deselect High Z
CMOS standby
X
X
VOHB VOUT2 Deselect High Z Battery-backup mode
Sept. 1996
2