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R3112X

LOW VOLTAGE DETECTOR WITH OUTPUT DELAY

RICOH Co.,Ltd. 

R3112x

OPERATION

Current Source

Vref

Ra Comparator

-

+

Rb

Tr.2

Tr.1

RD

Schmitt Trigger

Rc

Output Capacitor

CD

VDD

Pch

OUT

Nch

GND

Fig. 1 Block Diagram with an external capacitor

1

Released Voltage +VDET

Detector Threshold -VDET A

Supply Voltage(VDD)

Minimum Operating VDDL

Voltge

GND

Output Voltage(OUT)

GND

2

3

4

5

HYSTERESIS

B

RANGE

Operation Status 1 2

3

45

Compartor(-) Pin

Input Voltage

I II

II

II I

Compartor Output L H Indefinite H L

Tr.1, 2

OFF ON Indefinite ON OFF

Nch OFF ON Indefinite ON OFF

Output Tr.

Pch ON OFF Indefinite OFF ON

Delay Time

I

Rb+Rc

Ra+Rb+Rc

VDD

II

Rb

Ra+Rb

VDD

Fig. 2 Operation Diagram

1. Output voltage is equal to supply voltage. (As for Nch open drain type, equal to pull-up voltage.)

2. When the supply voltage is down to the detector threshold voltage level(Point A),

Vref >= VDD×(Rb+Rc)/(Ra+Rb+Rc) is true, then output of the comparator is reversed from “L” to “H”, therefore

output voltage becomes GND level.

3. When the supply voltage is lower than minimum operating voltage, the operation of output transistor is

indefinite. In the case of Nch open drain type, output voltage is equal to pull-up voltage.

4. Output Voltage becomes GND level.

5. When the supply voltage is higher than released voltage (Point B), Vref <= VDD×Rb/(Ra+Rb) is true, then

output of the comparator reaches the threshold level, and Output of Shmitt Trigger is reversed from “H” to

“L”, then output voltage is equal to supply voltage. (As for Nch open drain type, equal to pull-up voltage.)

∗) The difference between released voltage and detector threshold voltage means hysteresis range voltage.

10

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