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TPS7A02: Dropout voltage at close to 0mA

Franz Schellhase
Expert 3605 points
Part Number: TPS7A02

Hi Team,

Why does the dropout voltage remain stable at 80mV even though the output current drops to ~0 mA ? Shouldn't it continue to drop since RDSon of the transistor is constant ? See graph from the data sheet:

Thank you,

Franz

  • 0
    TI__Mastermind 38115 points

    Hi Franz,

    RDS_on isn't actually constant, but it is close to constant when the pass FET is fully on, and when the load current is small the pass FET is not all the way on. I believe the minimum dropout voltage that you can notice by comparing Figures 32 and 33 is because of the required gate voltage to get the VGS of the pass FET into the saturation region. I.e. the larger VOUT requires a larger gate voltage for the pass FET to be fully on and hence the dropout voltage does not start rising until the load current becomes large enough that the pass FET needs to be turned fully on, at a higher point than for the lower VOUT device. 

    Regards,

    Nick