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LP2951-N: Vout calculation

Yee Yong Teo
Expert 4335 points
Part Number: LP2951-N

Hi,

We have design needs very accurate output. So, we are taking the full equation Vout = Vref * (1 + R1/R2) + IFB*R1. For IFB*R1, should this portion be negative? Means need to minus of IFB*R1?

Thanks.

- YY

  • 0
    TI__Expert 4435 points
    Hi YY,

    The FB pin bias current flows into the FB pin. In the LP2951-N datasheet, this is represented as a pin current of -20 nA (20 nA flowing into the pin). This current will come from Vout, flow through R1 and then into FB pin. By V=I*R, the added FB current increases the voltage across R1, thus this term is positive in the Vout equation. Use IFB = 20 nA.