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LM5157EVM-BST: Output Voltage Droop

Jexy Liew
Prodigy 110 points
Part Number: LM5157EVM-BST

Hello team,

Our customer has tested LM5157EVM and changed R13 from 4.53K to 1.1K to get 46V output. However, while setting the input voltage to 4.2V, the output voltage dropped to 33V. What are the possible reasons for the drop in output voltage? 

  • 0
    TI__Guru 52875 points

    Hello Jexy,

    Probably the converter is going into current limit? The input current is around 12 times as big as the output current, if the input voltage is 1/12 the output voltage. Possibly the power supply is not able to deliver the current or the inductor is going into saturation.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    TI__Prodigy 110 points

    Hello Brigitte,

    Thanks for your support on this. The customer is providing 4.1V/3A from the input and the output has no load. They are still seeing the 33V instead of the expected 46V.

    From my understanding, that is a high input current coming in the circuit at 3A with no load. What pointers would you recommend for the customer to measure?

  • 0 in reply to Jexy Liew
    TI__Expert 7685 points

    Hi Jexy,

    Thank you for your reply, maybe waveforms of the Vin, Vout, SW node, and inductor current if possible during normal operation and start-up would be a good starting point.

    BR,

    Haroon