MPM3840 Fails to Start

DC-DC Power Converters
1

Hello!

I use MPM3840 in my project, please check the scematic below. PCB was designed as recommended bu MPS User Manual.

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Incoming 5 V is tested OK, but there is only about 500 mV output voltage, which does not depend on EN input level.
I have 2 MPM3840 in my circuit, with the same problem.
Please help me to solve the issue.

With regards,
Maksim

2

Hi bigdeal2000,

Thanks for posting on the MPSNow Forum.
Can you provide some scope shots of the following? Vin, SW, EN, PG, Vout

Thanks,
Cindy

3

Hi cindy,yu!

I checked those pins with a scope:
Vin == 5 V constantly
SW == 0.6 V constantly
EN == 0.6 V when floating and about 4V during test
PG == 0.6 V
Vout == 0.6 V
There is not pulse/spikes/waves, which can be treated as DC/DC start-up attempts. Just stable voltage.

Thank you!
With regards,
Maksim

4

Everything is Ok, there was a hard-to-find soldering problem - Vin did not actually apllied to IC pin.

Thanks for your attention.
With regards,
Maksim