Application information

VND810SP

18/27

Doc ID 7377 Rev 5

3.4

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.

Figure 25.

Open-load detection in off-state

VOL

V batt.

VPU

RPU

RL

R

DRIVER

+

LOGIC

+

-

INPUT

STATUS

VCC

OUT

GROUND

IL(off2)

Obsolete

Product(s)

- Obsolete

Product(s)