VN820 datasheet(6/35 Pages) STMICROELECTRONICS

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VN820 / VN820SO / VN820SP / VN820-B5 / VN820PT

OPEN LOAD DETECTION IN OFF STATE

Off state open load detection requires an external pull-up

resistor (RPU) connected between OUTPUT pin and a

positive supply voltage (VPU) like the +5V line used to

supply the microprocessor.

The external resistor has to be selected according to the

following requirements:

1) no false open load indication when load is connected:

in this case we have to avoid VOUT to be higher than

VOlmin; this results in the following condition

VOUT=(VPU/(RL+RPU))RL<VOlmin.

2) no misdetection when load is disconnected: in this

case the VOUT has to be higher than VOLmax; this

results in the following condition RPU<(VPU–VOLmax)/

IL(off2).

Because Is(OFF) may significantly increase if Vout is pulled

high (up to several mA), the pull-up resistor RPU should

be connected to a supply that is switched OFF when the

module is in standby.

The values of VOLmin, VOLmax and IL(off2) are available in

the Electrical Characteristics section.

VOL

V batt.

VPU

RPU

DRIVER

LOGIC

INPUT

STATUS

VCC

OUT

GROUND

IL(off2)

Open Load detection in off state

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