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TPS759: TPS75901KTTR Input Current

Calvin Khoo
Prodigy 30 points
Part Number: TPS759

Tool/software:

Dear TI,

I'm using the TPS75901KTTR, with 5V input voltage (from a power supply) and 3.3V output voltage. From the datasheet, it says "Quiescent current is 125 µA at full load", it led me to believe that the input current is only 125uA even at 7.5A output current. However, when I tested it with output connected to a DC electronic load in constant current/resistance mode, whatever output current I'm using, the input current is the same value, eg if output current = 1A, the input current is also 1A, so the input current was never 125uA. With this, please help me with my questions below?

1. Is the input current = output current?

2. If the input current = output current, does that create a lot of heat given the input power is always much higher than output power?

Would appreciate if you can help advise.

Thank you.

Regards,

Calvin

  • +1
    TI__Expert 5410 points

    Hi Calvin,

    Thank you for asking us!

    1. Input current = Output current + Quiescent Current 

    but in most cases output current is orders of magnitude higher so it may be well approximated by Input Current = Output Current

    The quiescent current is the additional current used to power the device that is not passed through to the output.

    2. Yes, it does create a lot of heat. In fact, power dissipation is usually the limiting factor in LDOs. The voltage difference between input to output is burned off as heat, see the equation from the datasheet below:

    This LDO is equipped with a thermal shutdown circuit, which helps prevent damage from overheating. Once the die temperature rises above 150'C, the output will shut down until it has cooled down enough. If the conditions still allow for enough power dissipation to overheat the device again, it will repeat the cycle. 

    Best,

    Gregory Thompson

  • 0 in reply to Gregory Thompson
    Prodigy 30 points

    Dear Gregory,

    That explains it, thank you.

    Regards,

    Calvin