s-8424a Seiko Instruments Inc., s-8424a Datasheet - Page 20

• Manufacturer Part Number: s-8424a
• Description: Battery Backup Switching Ic
• Manufacturer: Seiko Instruments Inc.

20
BATTERY BACKUP SWITCHING IC
S-8424A Series
3.2 V
3.3 Switch Controller
The V
VOUT pin voltage rises to V
voltage is more than the CS release voltage ( + V
output voltage of voltage regulator 2 (V
the V
The CS pin output remains high if the VIN pin voltage stays higher than the CS detection voltage ( − V
when the VOUT pin voltage drops to less than the V
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
Power Supply Voltage (V
The switch controller sets voltage regulator 2 ON and switch transistor M1 OFF from the initial status
until the primary power supply voltage V
voltage ( + V
detector 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 14 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.
Detector
SW2
SW2
voltage when the VIN pin voltage drops to less than the CS detection voltage ( − V
detector monitors the VOUT pin voltage and keeps the CS release voltage output low until the
V
V
IN
IN
> V
< V
DET1
SW1
SW1
) in order to prevent consumption of the backup power supply regardless of the V
Table 14 ON/OFF Switching of Voltage Regulator 2 and
IN
SW2
)
Seiko Instruments Inc.
voltage . The CS pin output then changes from low to high if the VIN pin
Switch Transistor M1 According to Power Supply Voltage (V
Voltage Regulator 2
IN
reaches more than the CS release voltage ( + V
OUT
OFF
). The CS pin output changes from high to low regardless of
ON
IN
DET1
IN
DET1
is connected and reaches more than the CS release
(or power supply voltage V
), the normal sequence status is entered, but until then
SW2
) when the VOUT pin voltage rises to 95 ± 2% of the
voltage due to an undershoot.
Switch Transistor M1
OFF
ON
BAT
) sequence: a special
DET1
IN
VOUT Pin Voltage
rises and becomes
).
DET1
V
BAT
Rev.2.2
V
IN
).
OUT
− V
. The time
dif
IN
)
DET1
_00
SW1
)