Unexpected behavior with MP8020 during turn-on

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1

Hi, I’ve started evaluating the MP8020 using the EV8020-QV-00A evaluation board. A basic first test was to just put a 300ohm resistive load between the VSRC and GND pins and connecting a 45W PSE.

The chip fails to start up properly when I do this. The voltage across the load stays around 37V, while the input is 57V. The PSE does not indicate any fault, so classification seems to have worked correctly. But the MP8020 gets really hot and the PG pin is not asserted.

A 300ohm load seems reasonable and well below any of the current limits. What exactly am I missing here?

2

Have you tried using any other input voltage? What do you mean by “really hot”? Could you also try putting the resistor at the Vout and GND of the EVB?

3

Hi, the problem seems to be that the MP8020 remains in constant current limiting mode (called inrush limit in the datasheet) during startup. If a resistive load is applied that requires a higher current than 75% of ILIM, the current never drops below 75% of ILIM. So the MP8020 stays in constant current mode indefinitely.