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LMR10510 efficiency issue

My customer asks:

We have a load at 3v3 that takes from about 100mA to about 400mA, depending on what’s turned on.

We’re trying to step down from USB input, so a nominal 5v0, but ranging from 4v5 to 5v5.

 

Trying it out at the low end of the load, I had a load current of 136mA, and a source current of 130 mA with a 5v0 input.  This gives me an efficiency of about 75%, when the data sheet would make me expect something in the low 90’s.

 

Circuit is very straight forward, pretty much right out of the data sheet.

 

LMR10510XMF

catch diode: MBRS2040LT3G (ONSemi)

Inductor: SRN4018-3R3M (Bourns)

2x 10uF ceramic input cap

2x 10uF ceramic output cap

 

Any ideas why I’m seeing such poor results?

  • We've received your query and will get back to you shortly.

    Thanks,
    Anston
  • Can you share your schematic with us?
    How are you measuring the input the output voltage? Please ensure you aren't measuring Vout at the load terminal.
    Vout and Vin should be measured directly across the input capacitors.
    Iin and Iout should be measured using calibrated shunts.

    Please also ensure you are using an inductor with low DCR and a design on a PC board. Breadboarded designs will not give the right efficiency.

    According to my calculations you should be seeing at least 85% efficiency.

    Thanks,
    Anston