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LMR43620: Mismatch between Reported Efficiency in datasheet & Measured efficiency of part when integrated in design

zoya arshad
Prodigy 10 points
Part Number: LMR43620

Above is a photo of our application. When SH300 & SH301 are cut to externally power input and load via eload at output for efficiency measurements, we are not seeing the efficiency that is reported in the spreadsheet that was provided to us during design phase by TI (Datasheet only had efficiency data for Vout = 3.3V). The spreadsheet showed efficiency in the 90s. Note that we did try multiple types of 4.7uH for L300, but efficiency results did not improve. We are seeing somewhere around efficiency 50-60% with Vin is 10-12V (Vout = 5V). Attaching sheet below. Please provide us guidance on why we are seeing this difference and/or suggestions on how to improve.

 LMR43620M5VEVM-1M_efficiency.xlsx

  • 0
    TI__Genius 10715 points

    Hello,

    Thanks for sharing the schematic and bringing up this question. 

    It looks like you're operating the device in FPWM mode which means the device will switch at constant frequency across load which will result in poor light load efficiency. Try tying the RT pin to GND to enable AUTO mode which will vary the frequency at lighter loads and achieve better efficiency.

    Also, the inductor in your schematic shows a DCR of 750mOhm which will contribute significant conduction losses and result in poor efficiency as well. I believe a XAL4030-472 was used for those efficiency measurements which has a typical DCR of 40mOhm for comparison. 

    Also when taking your efficiency measurements, be sure to measure the input/output voltage as close to the in/out capacitor as possible to avoid conduction losses. I'll typically solder wire directly across the input/output cap for this. 

    Regards,

    Harrison Overturf