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LP5907: Minimum Vin for 4.5V Vout?

Duncan MacGregor
Intellectual 470 points
Part Number: LP5907

We have an application where we are considering the LP5907 as a low-noise supply for a 4.5V rail with a 20-40 mA load. The input voltage is planned to be 5V which appears to meet the 250 mV max drop-out voltage spec. However in the data sheet there is an application note (section 9) "To ensure that the LP5907 output voltage is well regulated and
dynamic performance is optimum, the input supply must be at least VOUT + 1 V." If that is true then we would need at least a 5.5V supply input.

The +1V statement appears to conflict with a specified maximum drop-out voltage of 250 mV.

Can you clarify the input voltage requirement?

Thanks - appreciate your help.

  • 0
    TI__Mastermind 23361 points

    Hi Duncan, 

    The headroom between Vin and Vout needs to be higher than the dropout for the LDO to regulate, but the higher margin is needed to achieve good PSRR and noise performance. That's why we recommend having higher than dropout headroom.

    Regards, 
    Jason Song