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LM53603: Vout > Vin

Part Number: LM53603

I use the LM53603 to supply Vout=5V to my circuit. I would like to have the option to feed 5V in from a secondary source while the LM53603 input can be 12V or floating.

The datasheet says "Don't: Allow the output voltage to exceed the input voltage, nor go below ground."

What precautions do I need to take to make this work? Would a diode from Vout to Vin be sufficient? I would like to avoid a series diode at the regulator output.

Vin is supplied from a battery via a reverse polarity protection diode within the device, so shorting to ground should not be an issue.

  • Hello Sebastian,

    If your input voltage can be lower than the output, you will need the input diode. The red diode, is sufficient to bypass the internal body Diode of the high side FET. I am assuming that the alternate supply is never present when the device is powered on, supplying 5V to the output. I suggest that this should be the case. If not, there could be a condition where the alternate supply can load the output. As a minimal precaution, suggest using another diode from the 5V alternate supply, to the output of the LM53603 to prevent the supply loading the output.

    Hope this helps?

    David.