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LM2776: How to calculate the input current

Kaji@PAN
Mastermind 7775 points
Part Number: LM2776

Tool/software:

Hello,

I would like to ask you about how to calculate the input current for the LM2776.
For general converters, the input current can be calculated from the formula Input power x efficiency = output power.
For a negative voltage output like the LM2776, what formula should I use to calculate the input current?
For example, if the input voltage is 5V, the output voltage is -5V, and the output current is 50mA,
is it okay to simply set the output power as |-5V| x 50mA = 0.25W and calculate the input current taking the efficiency into account?

Best regards,

  • +1
    TI__Mastermind 22080 points

    Hello Kaji,

    thanks for using E2E.

    I think for average input current you can calculate from the efficiency as you already described. Please be aware that the abs. output voltage will be a little less than the input voltage due to the losses. The WEBENCH ® Power Designer tool is estimating Vout = -4.88V at 94% efficiency for your use case. So the average input current for this use case would be 51.92mA.

    Best regards,

    Andreas.