8

Open-load

In order to detect the open-load fault, a pull-up resistor must be connected between the VCC line and the output

pin.

In a normal condition, a current flows through the network made up of a pull-up resistor and a load. The voltage

across the load is less than VOLMIN and the DIAG pin is kept high.

This is the result in the condition:

Equation 1:

VCC [RLOAD / ( RLOAD + RPU )] < VOLMIN

or

Equation 2:

[(VCC / VOLMIN) - 1] RLOAD < RPU

When an open-load event occurs the voltage on the output pin rises to a value higher than VOLMAX (depending on

the pull-up resistor) and the diag pin goes down.

This is the result in the condition:

Equation 3:

RPU < (VCC - VOLMAX) / |IOUT(OFF1)MIN|

Figure 8. Open-load detection

VNI2140

Open-load

DS5977 - Rev 11

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