RX8130
CE
Page
30
ETM50E-05
4) SMPTSEL1, SMPTSEL0 bit
V
DD
voltage drop detection (V
DET2
) constantly monitors the main supply voltage applied to VDD-pin and in case
VDD drops below -VDET2 voltage, the power supply is switched from VDD to VBAT. For the monitoring of the
VDD voltage, it is necessary to switch the MOS-switch SW1 (SW1 is located between the V
DD
-V
OUT
) off for the
measurement time (to avoid measuring the voltage on VOUT-pin or supplied from VBAT).
Adjusting these bits allows to adopt the effective VDD Monitoring time to the discharge behavior on VDD and
thus allow to make sure to grasp voltage drops safely.
Since VDET2 voltage detection is performed continuously and not only during the time SW1 is off, it is possible
to detect VDD voltage drops under certain conditions at any time and not only when SW1 is off. To safely detect
the VDD voltage drop, SW1 however has to be opened and SMPTSEL-registers need to be set carefully.
These registers do as well control the detection timing for the full charge detection (V
DET3
) and Low-VBAT
detection (V
DET4
), which will control SW2.
Voltage detection (VDET1, VDET2, VDET3 and VDET4) times in different operation stages:
Power supply operation mode
V
DD
operation
(Backup battery is
charging)
V
DD
operation
(Backup battery is
fully charged)
VDD operation
(After return from backup
V
DET1
>V
DD
>V
DET2
)
SMPTSEL1,0
SW1 Off time.
*
00b (default)
2ms
2ms
2ms
01b
16ms
16ms
2ms
10b
128ms
128ms
2ms
11b
256ms
256ms
2ms
* Time values in above list are only for reference.
Operation stages of voltage detection:
Power supply
operation mode
VDD operation
(Backup battery is
charging)
VDD operation
(Backup battery is
fully charged)
VDD operation
(After return from backup
V
DET1
>V
DD
>V
DET2
)
VBAT operation
(Backup mode)
Reset & I/F stop
threshold detection
V
DET1
Constantly ON
Constantly ON
Constantly ON
Constantly OFF
Power switching
detection
V
DET2
Constantly ON
Constantly ON
Constantly ON
Once/31.25ms
Full charge detection
V
DET3
Once/1.0s
Once/1.0s
Once/1.0s
Constantly OFF
Low-VBAT detection
V
DET4
Once/1.0s
Once/1.0s
Once/1.0s
Constantly OFF
*
In V
DD
operation the MOS-switch 1 has to be opened (Off) to detect the VDD voltage supply. Above mentioned times
for VDD monitoring correspond to this MOS-switch Off (opening) times.