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TPS82740B: maximum output current vs Vin (100mA or 200mA?)

JasonT
Intellectual 270 points
Part Number: TPS82740B

Hello, I would like to get clarification on the maximum total output current shown in the TPS82740B datasheet.

I am using the TPS82740B to generate Vout = 3.3V from Vin = 4.0V. I am also using the load switch to control a separate 3.3V rail.

Section 7.3 of the datasheet specs maximum Iout + Iload as follows:

      Voutnom + 0.7V <= Vin <= 5.5V            max = 200mA

      Voutnom <= Vin <= Voutnom + 0.7V     max = 100mA

Both of these are true in my case, so I don't know if my maximum is 200mA or 100mA or somewhere in-between. It seems like the spec is trying to say that if you don't have at least 0.7V of headroom then you can't source 200mA, but I don't know why there would be an abrupt drop from 200mA to 100mA. To add to the confusion, all of the efficiency curves run to 200mA (no derating for any Vin/Vout combination).

Thanks for any feedback.

- Jason

  • +1
    TI__Expert 7585 points

    Hi Jason,

    Thank you for your question.

    You are right, there is not an abrupt drop when the device reaches the 0.7V threshold, but this limitation is mainly due to thermal reason.

    When the VIN gets close to VOUT, the device enters the so called  '100% Mode'. In this operation condition, the device stops switching and keeps the high side Mosfet always on. Please refer to the datasheet for further information on the 100% Mode.

    In this condition, the power dissipation on the high side Mosfet could be too high to keep a DC current of 200mA for a relatively long time and it could risk to degrade the device performance.

    To avoid thermal problems the Recommended Operating Conditions advise to keep the current under 100mA,  to limit this power dissipation on the High side Mosfet.

    Please consider this recommended current limitation if your VIN drops below Voutnom + 0.7V (0.7V is the save headroom to assure correct operation).

    Please ask again if you need further support.

    Thanks,

    Stefano

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).