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LMP8481: LMP8481-H at voltages less than 10V and low Rload values

Gary Christison
Prodigy 40 points
Part Number: LMP8481

At 5V and low Rload, gain is low. Vcc is connected to Rsense as in your typical application schematic, page 1 of datasheet.

My schematic Rsense= 0.1 ohm, RefA and RefB are grounded, unidirectional current flow

Typical  Iload= 1A, Rload= 4.9 ohms with measured Vsense= 0.1V

Vout should be 10V. It's a lot lower, about 6V (gain no longer 100X) Increasing Rload to 10 ohms gives correct results.

If I disconnect Vcc from Rsense and bring in Vcc externally, circuit works at 5V/1A if powered with Vcc= 12V.

Am I missing something when interpreting the datasheet? As a minimum, I need a criteria for changing to external Vcc.

Thank you.

  • 0
    TI__Mastermind 26485 points

    Hello Gary,

    Your Vout of LMP8481 is limited to your VCC in voltage. That is why when you power it with 12V it is able to go all the way to 10V. I do not know how you are able to get above 5V at Vout when you have VCC. Unless you have something else pulling the voltage up. Hope this helps.

  • 0 in reply to Javier Contreras4
    Prodigy 40 points

    The datasheet says that the supply voltage doesn't have to be larger than the load source voltage. A 76V load source works with a 5V supply.

    My understanding is that there is an internal regulated source that provides 14V internally and that regulator works down to a min voltage of 4.5V

    Just need clarification, I'm probably having trouble with the datasheet's wording, should I be adding, but a 5V load source does not work with a 5V supply?

    The guidance I'm giving is that if load source is less than 10V, you need to bring in Vcc externally, but I don't have a source or justification for that guidance.

  • 0 in reply to Javier Contreras4
    Prodigy 40 points
    After reading through the datasheet, it looks like paragraph 8.3.10 has the criteria I'm looking for and that matches your solution.

    Thank you