FUJITSU MB3891 - Manual (Page 23)

MB3891
23
■ ■ ■ ■ FUNCTIONAL DESCRIPTION
(1) MAIN UVLO/BACKUP UVLO
Transient power-on surge states or sudden drops in supply voltage (VBAT2) can cause an IC to operate abnor-
mally, leading to destruction or damage to system elements. To prevent this type of fault, the undervoltage lockout
circuits (UVLO/ Backup UVLO) will shut off the output from OUT1 to V-BACKUP if the supply voltage falls below
the UVLO circuit threshold voltage (3.0 V/2.8 V typ.). System operation is restored as soon as the supply voltage
rises above the UVLO circuits threshold voltage (3.2 V typ.).
(2) LDO1
The LDO1 circuits uses the reference voltage supply and generates an output voltage (2.1 V typ.) at the OUT1
terminal (pin 12,13). Power can be drawn from the OUT1 terminal for external use, up to a maximum load current
of 120 mA.
(3) XPOWERGOOD (RESET)
When the OUT1 terminal (pin 12,13) voltage exceeds 2.0 V (typ.), after a delay interval set by a capacitor
(C
DELAYCAP
) connected to the DELAYCAP terminal (pin 18), the XPOWERGOOD terminal (pin 17) goes to “H”
level and resets the microcomputer. At the same time, the LDO2, LDO3, and LDO4 output is controlled ON/OFF.
(4) LDO2
The LDO2 circuit uses the reference voltage supply and generates an output voltage (2.8 V typ.) at the OUT2
terminal (pin 6,7) when the XPOWERGOOD terminal (pin 17) voltage is at “H” level and an “H” level signal is
input at the CONT2 terminal (pin 16). Power can be drawn from the OUT2 terminal for external use, up to a
maximum load current of 50 mA.
(5) General Purpose switches
Any of the OUT terminals can be connected to any SW-INPUT terminal so that when the corresponding SW-
ON terminal is at “H” level, the OUT terminal voltage can be drawn from the associated SW-OUTPUT terminal.
(6) LDO3
The LDO3 circuits uses the reference voltage supply and generates an output voltage (2.8 V typ.) at the OUT3
terminal (pin 3,4) when the XPOWERGOOD terminal (pin 17) voltage is at “H” level and an “H” level signal is
input at the CONT3 terminal (pin 56). Power can be drawn from the OUT3 terminal for external use, up to a
maximum load current of 100 mA.
(7) LDO4
The LDO4 circuits uses the reference voltage supply and generates an output voltage (2.8 V typ.) at the OUT4
terminal (pin 40,41) when the XPOWERGOOD terminal (pin 17) voltage is at “H” level and an “H” level signal is
input at the CONT3 terminal (pin 56) , and an “L” level signal is input at the CONT4 terminal (pin 44). When an
“H” level signal is input at the CONT4 terminal, the output voltage at the OUT4 terminal is 2.5 V (typ.). Power
can be drawn from the OUT4 terminal for external use, up to a maximum load current of 100 mA.