15 Battery backup switchover function
RX8130CE
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ETM50E-07
Seiko Epson Corporation
43
3) SMPTSEL1, SMPTSEL0 bit
V
DD
voltage detection: V
DET
1 (reset), V
DET
2 (voltage down):
Battery backup detection (V
DET
2) is done constantly and SW1 is opened periodically for V
DD
measurement.
During SW1:ON, external voltage to V
DD
cannot be measured precisely because RTC internal voltage is
leaked to V
DD
external voltage supply circuit even external circuit is down. So periodical SW1 = OFF
makes disconnection between RTC internal voltage and external voltage supply, thus V
DD
external voltage
is measured precisely. V
DD
external voltage drop moves to backup mode.
See
V
BAT
voltage detection: V
DET
3 (V
BAT
full charge), V
DET
4(V
BAT
over discharge)
In case of normal mode, V
BAT
voltage is precisely and periodically detected with condition (SW1 OFF,
SW2 OFF). The detection period is determined by combination of SMPTSEL1, SMPTSEL0.
See
(In case of CHGEN = 0, There is no charge operation SW2 = OFF)
Table 36 Voltage detection timing
Power supply mode
Normal mode
(Backup battery is
charging)
Normal mode
(Backup battery is
fully charged)
Normal mode
(After return from backup
V
DET1
>V
DD
>V
DET2
)
Backup mode
Reset detection
V
DD
< V
DET1
Constantly ON
Constantly ON
Constantly ON
Constantly OFF
Power switching
detection V
DD
<
V
DET2
Constantly ON
Constantly ON
Constantly ON
Once/31.25 ms
Full charge detection
V
BAT
> V
DET3
Once/1.0 s
Once/1.0 s
Once/1.0 s
Constantly OFF
Low-V
BAT
detection
V
DD
< V
DET4
Once/1.0 s
Once/1.0 s
Once/1.0 s
Constantly OFF
*
In normal mode, when operating the RTC on V
DD
-supply, SW1 has to be opened (Off) to perform the V
DD
voltage
detection for below mentioned times
Table 37 VDET3, VDET4 intermittent detection period
Power supply operation mode
V
DD
operation
(Backup battery is
charging)
V
DD
operation
(Backup battery is
fully charged)
V
DD
operation
(After return from backup
V
DET1
>V
DD
>V
DET2
)
SMPTSEL1,0
SW1 Off time. *
00b (default)
2 ms
2 ms
2 ms
01b
16 ms
16 ms
2 ms
10b
128 ms
128 ms
2 ms
11b
256 ms
256 ms
2 ms