MP24971 not starting

Using the MP24971 as a 5volt power supply for a small usb microcontroller project.

We are having issue when we test supply failure and create many on / off events in a short amount of time. (similar to when customer plugs the unit in and fumbles with the plug creating many short power events).

The MP24971 does not startup, and does not recover. We have 0.8 Volts on the output, and 5V on the Bootstrap pin. Input voltage is 12 Volts. Current draw on the entire project is 180mA. Unplugging for 2 seconds and then repowering, the device starts as expected. We see this event after approximately 20 restarts.

The Datasheet refers to Output Over-Voltage protection. where the part will be “lathed” off (page 9) after a timer delay. There is no indication in the datasheet to show when the chip is in this Over voltage state. I suspect that the translation “lathed” off refers to “Turned” off.

I have been working on this all day. So far, it looks like a spike when the inductor is collapsing during the power off interval. It triggers the OVP Comparator and stays in Shutdown. Fitting a 5.6V zener from the input of ISN (pin 5) to ground seems to reduce the spike, and disable this feature and stops any spikes from turning off the chip. Luckily we don’t see any voltages higher than 6 Volts and this is not a danger to the circuit.

Hi Ken,

Welcome to the MPS Technical Forum! Do you represent a company working on designing MPS into a new product?
It’s good to hear that the issue is resolved for now. Can you please share a schematic of your system? Is the additional Zener diode the only change you made to prevent the device from triggering OVP?

Thanks Bryan. Yes. Due to the shortage of parts around the globe. I had to source something quickly and that suited our requirements. We had 25 units built when we discovered the issue.
We tried several changes. Increasing Filter capacitance to ISN and ISP. The extra diode for Bootstrap. and Extra capacitance on the VOS input.
Due to conducted emissions issues previously, we have adopted a murata designed filter at the input. This may have something to do with the start. But we believe the MP24971 may have issues with the over voltage detection.