MP9488 stability issues

DC-DC Power Converters
1

We are using the MP9488 almost in the same way as on page 18 of the rev1.0 MP9488 datasheet. When supplied with 24 V up to 96 V it works as expected. But if it’s supplied with voltages above 96 V the resulting output is not stable.

The circuit is as follows and should produce a 12V output voltage from a 24-350V input:

image
image901×303 49.2 KB

It was tested using no load apart from the 3k resistor R1. If supplied with more than 96 V, the output shows the following behavior (yellow = Vout, green = SW):

SCR11
SCR111280×824 44.8 KB

SCR10
SCR101280×824 44.5 KB

As L_out we are using the 1mH inductor SDCH1V6045-102M-R, which has a saturation current of 450 mA. Could this be caused by a saturation current that is too low?

2

Hi Adrian,

Can you help share some scope shots of what it looks like working from 24V-96V? Can you also help share the inductor current waveform as well as the waveform for VCC?

From the scope shots you shared it looks like the part is hitting the current limit and the switching stops.

3

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