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BD3021HFP-M

Regulator with Voltage Detector and Watchdog Timer

ROHM Semiconductor 

BD3021HFP-M

Technical Note

●BD3021HFP-M (Power on Reset / Watchdog Timer)

Power ON reset (output delay time) is adjustable by CT pin capacitor.

TdLH(S) ≒(1.15V×CT capacitance(µF) / Ictc(µA) (Typ.)

・TdLH

:Output delay time( power ON reset)

・1.15V

:Upper switching threshold voltage(Typ.)

・CT capacitance :capacitor connected to CT pin

・Ictc

:WDT charge current

Calculation example) with 0.01µF CT pin capacitor

TdLH(S)=1.15V×0.01µF/6µA

≒1.9msec

※If the CT capacitance is not the same as the condition on the electrical characteristics table, i.e., 0.01µF, choose the capacitance value in ratio referring

to the above equation.

Watch Dog Timer ( WDT watch time, reset time) is adjustable by the CT pin capacitor

TWH(S) ≒(1.00V×CT capacitance (µF))/ Ictd(µA) (Typ.)

TWL(S) ≒(1.00V×CT capacitance (µF))/ Ictc(µA) (Typ.)

・TWH

:WDT watch time (delay time to turn the reset ON)

・TWL

:WDT reset time (time the reset is ON)

・1.00V

:Upper switching threshold voltage － lower switching threshold voltage

・CT capacitance :CT pin capacitor ※Shared with power ON reset

・Ictc

:WDT charge current

・Ictd

:WDT discharge current

Calculation example) with 0.01µF CT pin capacitor

TWH(S)≒1.00V×0.01µF/2µA≒5.0msec (Typ.)

TWL(S)≒1.00V×0.01µF/6µA≒1.7msec (Typ.)

※If the CT capacitance is not the same as the condition on the electrical characteristics table, i.e., 0.01µF, choose the capacitance value in ratio referring

to the above equation.

＜Timing Chart＞

13.5V

Vcc

4.0V

3V

0V

4.60V

5V

VOUT

4.0V

0V

4.50V VHS 100mV

1.25V

CT 1.15V

0.15V

0V

CT pull up voltage

CLK

0V

RESET

OUT voltage

0V

Reset ON

Power on reset

Power on reset

Reset ON

Reset ON

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7/14

2010.11 - Rev.A

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