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LM25116 Current Gain Insufficient - Excessive Shunt

Tyler Christensen0
Prodigy 70 points
Other Parts Discussed in Thread: LM25116

I'm working on a design with a 5V LM25116 based regulator with an intended current limit of 4A which has 5V output. To achieve this, I'm getting nearly 40mOhm of shunt requirement which becomes the dominant power loss of around half a watt. The shunt gets far hotter than any other component during operation.

This is not really acceptable to have the dominant loss be a sense element. Is there anything I can do to keep the current limit with a lower shunt? Presumably I could add an external amplifier but that would be a major revision to the design. Are there any tricks with external resistors to increase the gain or increase the offset above the internal 0.5V? Or lower the 1.6V overcurrent threshold?

  • 0
    TI__Mastermind 21720 points

    Hi Tyler,

    There is no way to externally change the 1.6V over current threshold voltage.

    The external amplifier is an option that would work well and keep the current limit accurate over temperature.

    The other option is that RDS(on) resistance sensing of the low side FET can be used. This is detailed on page 15 of the datasheet. This would be a simple change, but please note that the RDS(on) resistance of a FET changes over temperature and will make the current limiting less accuracte than using a sense resistor.

    -Garrett