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LMR38025: LMR38025 burnt when VIN=VOUT

Angel Garcia
Prodigy 50 points
Part Number: LMR38025

Tool/software:

Hi,

I'm using a LMR38025 for getting 12V from a 14S battery.

It works fine but if the input voltage is 12V (same as in the output) the chip is burnt.

From the datasheet I found a note saying that if the input voltage is lower than the output voltage the capacitors would be discharge through the internal parasitic diode between VIN and SW, is this the reason why the chip is been burnt when supplied at 12V? Would it be solved by placing a Schottky diode between VIN and VOUT as it is mention in the datasheet?.

Thanks in advance.

Kind regards.

  • 0
    Prodigy 50 points

    The circuit modified, adding the Schottky diode (Vr=100V) between VIN (up to 60V) and VOUT (12V).


  • 0
    TI__Mastermind 31255 points

    Hi Angel,

    Which pin of the chip is burnt? If it is at the VIN pin, that is a possible reason as the diode could get hot and damage the device thermally. The schottky diode placed between VIN and VOUT is used to protect the device, but seeing as the voltage are the same, I suspect it may not be the true cause since the diode may not conduct at all. 

    Another possibility of damage could be current flowing all the way back into the input source too. You may need to place a diode from the input source (anode) to VIN pin (cathode). Can you also try that?

    Thanks,

    Richard 

  • 0 in reply to Richard Fu22
    Prodigy 50 points

    Hi Richard,

    Thanks for your answer. 

    Not sure about which pin is burnt but it is in the VIN side.

    It makes sense that at VIN=VOUT the current would not flow through the diode, but if the problem is the current flowing into the input source, why at higher a voltage the circuit works fine?

    I'll try both solutions and I'll let you know.

    Thanks again.

  • 0 in reply to Angel Garcia
    TI__Mastermind 31255 points

    Hi Angel,

    At higher input than regulation target, current cannot flow back through the parasitic body diode of the high side switch.

    Let me know how the changes go. 

    Thanks,

    Richard