s-8426a Seiko Instruments Inc., s-8426a Datasheet - Page 11

• Manufacturer Part Number: s-8426a
• Description: Battery Backup Switching Ic
• Manufacturer: Seiko Instruments Inc.

Rev.1.0
Table 6 ON/OFF Switching of Voltage Regulator 2 and Switch Transistor M1 According to Power Supply Voltage (V
Power Supply Voltage (V
3. 1 V
3. 2 V
3. 3 Switch Controller
_00
V
V
IN
IN
The V
controller. The detection voltage (V
In the products V
following equation.
The V
pin voltage rises to V
more than the CS release voltage (+V
voltage regulator 2 (V
the VIN pin voltage drops to less than the CS detection voltage (−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
special sequence status is maintained.
(1) Special sequence status
(2) Normal sequence status
> V
< V
SW1
SW2
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 6 according to the power supply voltage V
for voltage regulator 2 to be switched from OFF to ON is a few hundred µs 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 µF 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.
SW1
SW1
Detector
Detector
SW2
SW1
DET1
detector monitors the VOUT pin voltage and keeps the CS release voltage output low until the V
detector monitors the power supply voltage V
) in order to prevent consumption of the backup power supply regardless of the V
+V
IN
)
DET4
SW2
SW2
> +V
= (−V
OUT
Voltage Regulator 2
). The CS pin output changes from high to low regardless of the V
voltage. The CS pin output then changes from low to high if the VIN pin voltage is
DET1
DET1
, the setting value is 77 ±2% or 85 ±2% of +V
) + 15 × { (−V
OFF
ON
SW1
Seiko Instruments Inc.
IN
DET1
) reaches more than the CS release voltage (+V
) can be set to 77 ±2% or 85 ±2% of the CS release voltage (+V
) when the VOUT pin voltage rises to 95 ±2% of the output voltage of
IN
DET1
) is connected and reaches more than the CS release voltage
DET1
) – 0.8 } ÷ 372
IN
) (or power supply voltage (V
), the normal sequence status is entered, but until then the
SW2
Switch Transistor M1
voltage due to an undershoot.
IN
BATTERY BACKUP SWITCHING IC
and sends the results of detection to the switch
OFF
ON
DET1
).
DET4
which is calculated with the
BAT
VOUT Pin Voltage
DET1
)) sequence: a special
IN
S-8426A Series
) rises and becomes
V
).
IN
BAT
. The time required
V
SW2
OUT
− V
voltage when
dif
SW1
DET1
detector
).
DET1
OUT
11
IN
)
)