Voltage sags with MP172A

I am attempting to recreate the EV172A-S-00A circuit which uses MP172A to get an output of 5V, 120mA.

The changes I made to the reference design for my circuit:

  • I added a 1A fuse (Littlefuse 37411000410) before the fusible resistor on my design.
  • Used ON-SEMI RGF1M diode instead of SRGC10MH
  • Used SMC ES1J diode instead of STTH1R06A

The issue I initially faced was that that the output voltage was 5.764V instead of 5V. I adjusted the values of R1 and R2 and got ~5.3V. It is still not 5V but it is acceptable for now.

The next issue that I faced was that the voltage would sag significantly as soon as there is any load connected to it. I recorded a large voltage drop with just 10mA draw.

EV172A-S-00A circuit: 5.171V at 0mA, 5.012V at 10mA
My original circuit: 5.764V at 0mA, 4.913 at 10mA
My circuit with modified resistor values: 5.368V at 0mA, 4.202 at 10mA

I am looking for some assistance with this issue. I don’t understand why the voltage is falling so greatly on my circuit, but does not drop as significantly on the EV172A-S-00A. The circuit is rated to handle up to 120mA and my current draw is not even close to its limit. Please let me know if there is something obvious that I am overlooking.

One of our FAEs from MPS Now has already reached out to you. So he will be helping you out to resolve the issue.

Please reach out to him if you have any further questions.