BQ2203A Datasheet, PDF (3/12 Pages) Texas Instruments – NV Controller With Battery Monitor

bq2203A
If a secondary cell is not to be used, the BCS pin must be
tied directly to VSS.
VCC falling below VPFD starts the comparison of BCS
and BCP. The BC input comparison continues until VCC
rises above VSO. Power to VOUT begins with BCS and
switches to BCP only when BCS is less than BCP minus
VBSO. The controller alternates to the higher BC voltage
when the difference between the BC input voltages is
greater than VBSO. Alternating the backup batteries al-
lows one-at-a-time battery replacement and efficient use
of both backup batteries.
To prevent battery drain when there is no valid data to
retain, VOUT, CECON1, and CECON2 are internally iso-
lated from BCP and BCS by either of two methods:
s Initial connection of a battery to BCP or BCS (VCC
grounded) or
s Presentation of an isolation signal on CE.
A valid isolation signal requires CE low as VCC crosses
both VPFD and VSO during a power-down. See Figure
2. Between these two points in time, CE must be
brought to VCC_*(0.48 to 0.52) and held for at least 700ns.
The isolation signal is invalid if CE exceeds VCC_*0.54 at
any point between VCC crossing VPFD and VSO.
The isolation function is terminated and the appropriate
battery is connected to VOUT, CECON1, and CECON2 by
powering VCC up through VPFD.
Battery Monitor—BCL, BCF
As VCC rises past VPFD, the battery voltage on BCP is
compared with a dual-voltage reference. The result of
this comparison is latched internally, and output after
tBC when VCC rises past VPFD. If the battery voltage on
BCP is below VBL, then BCL is asserted low. If the bat-
tery is below VBF, then BCL and BCF are asserted low.
The results of this comparison remain latched until VCC
falls below VPFD.
VCC
VPFD
CE
VSO
0.5 VCC
700ns
TD220101.eps
Figure 2. Battery Isolation Signal
Truth Table
Input
CE
A
H
X
L
L
L
H
CECON1
H
L
H
Output
CECON2
H
H
L
Nov. 1994 B
3