MB3790PFT View Datasheet(PDF) - Fujitsu

Part Name

Description

Manufacturer

MB3790PFT

Battery Backup IC

Fujitsu 

MB3790

(4) Momentary power failure or voltage dip

When the power supply voltage drops less than or equal to VINL. (4.2 V typ) as the power supply goes down or its

voltage dips momentarily, the RESET pin outputs a High level and the RESET pin outputs a low level. The devices

such as SRAM or a microprocessor are thereby placed in the standby mode and powered from the battery. When

in this mode, the primary battery voltage detection and the secondary battery recharging operations are stopped.

Note: To guarantee backup operation in case of momentary power failure, make sure the 5 V-to-0 V fall time on VIN

is 50 µs or more by using, for example, a capacitator.

2. Alarm Operation

V BAT1

DV BAT2 DV BAT1

V BATH1

V BATL1

V BATH2

V BATL2

ALARM1

(1)

(1)

ALARM2

(2)

(2)

If the primary battery voltage decreases while the power supply voltage (VIN) is greater than or equal to VINH (4.3 V

typ), alarm signals are output as described below. At this time, if the VBAT1 pin is released open, the output from the

alarm pin becomes indeterminate.

(1) Primary battery replacement alarm (alarm-1 output)

If the primary battery voltage drops to VBAT1 (2.65 V typ), the ALARM1 pin is forced to a Low level to issue an alarm

indicating that it’s time to replace the primary battery.

(2) Primary battery minimum voltage alarm (alarm-2 output)

If the primary battery voltage further drops to VBAT2 (2.37 V typ), the ALARM2 pin is forced to a Low level to issue

an alarm indicating that the primary battery power has dropped below the voltage necessary to retain the SRAM

data (approx. 2.0 V).

7

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