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TPS62740: Efficiency when in 100% mode operation

Fabio Leitao
Prodigy 150 points
Part Number: TPS62740


Tool/software:

Hi TI team,

We have been doing some measurements using the TPS62740 considering light output current loads.
In our design the output voltage was set to 2.8V and the output load is ~2uA.
The following graph shows the relation between voltage input and the current input for this configuration.

 

It is visible that when the input voltage gets close or lower to the output, the converter enters in the 100% mode operation and we also observed that the "output follows the input"

However, we where expecting the efficiency to be within or similar to the overall input range or lower, as it is maybe behaving as a pass-through device.
Could you provide more information about the expected efficiency when operating in 100% mode, or give some comments on the results?

Thank you for your support.

Fabio

  • 0
    TI__Mastermind 21580 points

    Hi Fabio,

    This is expected behavior. The IQ in 100% is higher than PFM since more internal circuitry like current limit etc. are switched on. In PFM all internal circuitry is off and the IQ can be very low. The efficiency can be below 1% in 100% mode with very light load like 2uA.

    Also if VIN is used for PG pin pull up, there can be some extra current through the external PG pull up resistor since PG can go to 0 in 100% mode.

    Best regards,

    Varun

  • 0 in reply to Varun John
    Prodigy 150 points

    Hi Varun,

    That sounds reasonable :)
    Thank you for the clarification.