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LM43601: Damage when Voltage Input gets shorted

Renan Santos Adriano
Genius 16500 points
Part Number: LM43601

Hello Team,

Good day.

My Customer would like to seek some advice for their application. Using the LM43601PWPR as a positive buck regulator(switcher) to take 13.8 Volts Vin to 3.3V Vout. While testing the design the Bench power supply leads feeding the switcher got shorted together while the switcher was running and providing 3.3 Volts. After the power leads were separated, the switcher failed to regulate and it only outputted 40mV. They do have overvoltage protection on the Voltage input but should they have a reverse biased diode connected across Vin and Vout to prevent back-feeding/reverse discharge of the output voltage into the LM43601 to the Voltage input?

Regards,


Renan

  • 0
    TI__Mastermind 28020 points

    Hi Renan,

    If they shorted the input leads, I'm not sure what part of the circuit they damaged. Were they able to probe the part and determine if the FETs were shorted or open? Did anything on the input side get damaged? Does Vin still come up to 13.8V?

    Regards, Jason

  • 0 in reply to J Arrigo
    TI__Genius 16500 points

    Hello Jason,

    Thank you for this response.

    They didn't probe the part at the time but what they saw that the input was able to come up to 13.8V and the output was only 0.04V. They replaced the part with a new one since they needed the prototype fixed. That is the first time they are using this switcher so they are trying to make sure this doesn't become an issue once they go to production. They know with linear regulators you would put a reverse-biased diode across the input and output so that if the input got shorted the output caps would discharge through the diode and not the regulator.

    Regards,

    _Renan

  • 0 in reply to Renan Santos Adriano
    TI__Mastermind 28020 points

    Hi Renan,

    Yes, if shorting of the input is a possibility, placing a diode across the input can be used. 

    This diode will prevent the input from going negative. I would a use schottky diode to reduce power loss.

    Regards, Jason

  • 0 in reply to J Arrigo
    TI__Genius 16500 points

    Hello Jason,

    We are still unclear on how you are recommending the application of the diode in your response(diagram would be helpful). My customer attached a snippet of their power supply schematic with the diode across the output to input and would like to know if this is OK? This should prevent the output from feeding back through the switcher if the input is shorted.

  • 0 in reply to Renan Santos Adriano
    TI__Mastermind 28020 points

    Hello Renan,

    I would not place the diode from VOUT to VIN. This will not prevent current from flowing through the device in the event of a input short. There is still a path through the body diode of the high side FET.

    I would place a series schottky on the input. See Fig 3 in Chapter 5 of the attached guide. There are a bunch of helpful protection circuits included.

    Regards, Jason