MP9942 shutting down from current draw

DC-DC Power Converters
1

Hi,
I’ve recently integrated an MP9942 into my system. However, when a load, that should draw over 400mA is applied, the part shuts down or doesn’t work as it should. Measured output before load is connected is 8V as expected, after load is connected, voltage is 4.6V. I’ve attached the schematic of what I have.
Many thanks,
Callum

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2

Hi,

I’m looking into this. Will get back to you asap.

Thanks,
Cindy

3

what is the value of R8, should be low like an ohm or two. what is the nature of your load? If your load is a switching power supply that turns on at a low Vin it can draw a high current and crush the upstream converter. If you can use PG or an UVLO to hold off the load until the 8V is established this can help

4

The value of r8 is 20 ohm. As stated on the data sheet. The load is connected after the 8v is established

5

Hi cpaustin1998,

I don’t see anything immediately wrong with your schematic, so I’ll need a better understanding what is actually happening on the board.
Please use an oscilloscope to probe Vin, PG, Vout and Iout and provide those screen captures.
Also, does the output voltage drop at < 400mA Iout?

Thanks,
Cindy