MB3790 Datasheet, PDF (6/21 Pages) Fujitsu Component Limited. – Battery Backup IC

MB3790
s DESCRIPTION OF OPERATION
1. Operation When the Input Voltage Goes On or Off
V IN
DV IN
V INH
V INL
V OUT
(1)
(2)
(3)
(4)
(2)
(3)
(4)
V IN-DV1
V BAT1-DVB1
t PO
t PO
RESET
V IN-DV1
V BAT1-DVB1
RESET
High level
Low level
High level Low level High level
V IN-DV1
Low level
High level
Low level High level Low level
(1) Power-on
While the power supply voltage is less than VINH (4.3 V typ), the protected devices such as SRAM or a microprocessor
are in the standby mode with the power supplied by the battery.
When the power supply voltage rises to a level greater than or equal to VINH, the PMOS transistor between the input/
output pins turns on and the power for such devices is supplied from the VIN pin. At the same time, the primary
battery voltage detection and the secondary battery recharging operations are actuated.
(2) Standby mode
When the power supply voltage rises to a level greater than or equal to VINH, the RESET pin outputs a High level
for the set duration of time and the devices such as SRAM or a microprocessor are held in the standby mode. Note
that the set duration of time can be adjusted by changing the capacitance of the CT pin.
The RESET pin outputs an inverted signal of the RESET pin.
(3) Active mode
The reset signal is cleared and the devices such as SRAM or a microprocessor are placed in the operating mode.
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