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LMR62014: 5V to 6V converter makes lot of heat and unstable output

Kyuhyong You74
Prodigy 20 points

Part Number: LMR62014

I have been testing above circuit to drive a scooter headlight unit rated for about 6 to 7VDC up to 0.5A from 5VDC input.

When turned on, led is bright enough but after about 10mins of use, brightness degrades and even flickering happens. 

The module becomes very hot when it happens. 

Is there anything wrong with the circuit?

For reference, I use VLS252010HBX-100M-1 for the Inductor.

  • 0
    TI__Mastermind 34201 points
    Hi Kyuhyong,

    After 10 mins of use, have you checked the waveform of Vout, SW pin?
    The input current can be calculated. Assuming efficiency is 85%, Iin=Vo*Io/Vin/Effi=7V*0.5A/5V/0.85=0.823A. The inductor Itemp(typ) is 0.8A, which means its temperature rise may up to 40C degree. I recommend you record the Vout, SW waveform and choose VLS252010HBX-4R7M-1. And Change C6 with a 10uF capacitor to give a higher phase margin.
  • 0 in reply to Zack Liu
    Prodigy 20 points

    Hi Zack, 

    Thanks for your prompt reply. I appreciate your advice. 

    I connected from a power supply which shows both voltage and current. At the beginning, there is about 0.5A / 5V into the converter for a while then it starts going down to 0.3A and so on.

    Should change the capacitor later and see how it improves. 

    Per the capacitor, do I have to use Tantal instead of mlcc? 

    Thanks,

    Kyu

  • 0 in reply to Kyuhyong You74
    TI__Mastermind 34201 points
    HI Kyu,

    The phenomenon is quite strange. When input current decreases down to 0.3A, can you measure the output voltage? And please tell me the headlight_out part number.
    You can have a try to use higher value output capacitor.
  • 0 in reply to Zack Liu
    TI__Mastermind 34201 points
    Hi Kyu,

    Any new latest news? I'll close this thread first since there is no reply. You can post new thread if still have any questions. Thanks.