MP2905 startup problem

DC-DC Power Converters
1

Good morning!

I have some problems with MP2905 IC:

  1. It always starts only with open-circuit on the load side. When some load applied at off state it sometimes starting at first time, sometimes not. Then it starts every one time.
  2. When I raise the output current to about 1 A the IC goes to failed state when there’s only a few impulses on the inductor at about 4 MHz and nothing more (see pic attached). Then I have to decrease load to about 0.2 A and MP2905 starts working. I have schematic made by the second scheme from appnote and it supposed to provide as much as 12A load current. My scheme is calculated for the output current 3 A.
    I tried to choose another inductor SRR1208-6R5 from Bourns and the current threshold raised up to about 1,5 A that is too far away from 3 A.

I’ll be very appreciated if you could help me. Thank you!

photo_2023-05-24_17-52-28
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2

What is the nature of your load? I would try first with a resistor. Sometimes electronic loads can give funny results

3

Thank you for your answer! I’m using ballast resistor, you can see it on the photo.

photo_2023-05-25_09-22-00
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4

Well that seems like a good choice, it won’t do anything funny during start up. Do you have an eval board?

5

No, I don’t. I thought: “What could be wrong with this simple device?”
I realized that it’s not as simple as I thought or I have a fake IC’s or simply I can’t guess what I’m doing wrong