s-8425 Seiko Instruments Inc., s-8425 Datasheet - Page 11

• Manufacturer Part Number: s-8425
• Description: Battery Backup Switching Ic
• Manufacturer: Seiko Instruments Inc.

Rev.2.3
( − V
3.2 V
The V
VOUT pin voltage rises to V
voltage is more than the CS release voltage ( + V
output voltage of voltage regulator 2 (V
V
The CS pin output remains high if the VIN pin voltage stays higher than the CS detection voltage
3.3 Switch Controller
The switch controller controls voltage regulator 2 and switch transistor M1. There are two statuses
corresponding to the power supply voltage V
sequence status and a normal sequence status. When the power supply voltage V
equal to or exceeds the CS release voltage ( + V
the special sequence status is maintained.
(1) Special sequence status
(2) Normal sequence status
SW2
DET1
The switch controller sets voltage regulator 2 ON and switch transistor M1 OFF from the initial status
until the primary power supply voltage V
( + V
status. This status is called the special sequence status.
The switch controller enters the normal sequence status from the special sequence status once the
primary power supply voltage V
Once the normal sequence is entered, the switch controller switches voltage regulator 2 and switch
transistor M1 ON/OFF as shown in Table 3 according to the power supply voltage V
required for voltage regulator 2 to be switched from OFF to ON is a few hundred μ s at most. During this
interval, voltage regulator 2 and switch transistor M1 may both switch OFF and the VOUT pin voltage
may drop. To prevent this, connect a capacitor of 10 μ F or more to the VOUT pin.
When the VOUT pin voltage becomes lower than the RESET detection voltage, the status returns to the
special sequence status.
voltage when the VIN pin voltage drops to less than the CS detection voltage ( − V
SW2
Power Supply Voltage V
SW2
_00
) when the VOUT pin voltage drops to less than the V
DET1
Detector
detector monitors the VOUT pin voltage and keeps the CS release voltage output low until the
Table 3 ON/OFF Switching of Voltage Regulator 2 and Switch Transistor M1
) in order to prevent consumption of the backup power supply regardless of the V
V
V
IN
IN
> V
< V
SW1
SW1
SW2
IN
According to Power Supply Voltage V
voltage . The CS pin output then changes from low to high if the VIN pin
Voltage Regulator 2
IN
reaches more than the CS release voltage ( + V
OUT
Seiko Instruments Inc.
). The CS pin output changes from high to low regardless of the
OFF
ON
IN
is connected and reaches more than the CS release voltage
DET1
IN
DET1
(or power supply voltage V
), the normal sequence status is entered, but until then
) when the VOUT pin voltage rises to 95 ± 2% of the
Switch Transistor M1
SW2
BATTERY BACKUP SWITCHING IC
voltage due to an undershoot.
OFF
ON
IN
BAT
VOUT Pin Voltage
DET1
) sequence: a special
IN
DET1
V
).
rises and becomes
BAT
S-8425 Series
V
).
OUT
− V
IN
SW1
dif
. The time
detector
11