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TPS62088: Hi iQ in continuous conduction mode

Daan Pape
Prodigy 50 points
Part Number: TPS62088
Other Parts Discussed in Thread: TPS62840

Hi,

I have made a simple evaluation PCB with the TPS6208833YFPT. As soon as the input is 3.35V the iQ is 5.9uA which is a bit higher then expected but ok. But as soon as the input is lower and the device goes into continuous conduction mode and there is no switching the iQ rises to 270uA which is way higher than expected. This is the schematic:

Is this high quiescent current to be expected in continuous continuous conduction (100% duty cycle) mode?

Kind regards,
Daan

  • 0
    TI__Mastermind 21580 points

    Hi Daan,

    The low IQ is when the device is in PFM mode with no switching. The IQ in 100% mode can be higher as the high side FET is completely turned on and the current consumption of internal circuits can also be higher in this mode. 

    Can you completely disconnect the output load to make sure there is no leakage current to the output in this mode?

    Best regards,

    Varun 

  • 0 in reply to Varun John
    Prodigy 50 points

    Hi Varun,

    Thank you for the fast reply. I have disconnected all output load to measure the iQ. I previously used the LM3281YFQR regulator which did not have this high iQ in 100% duty cycle mode and therefore I was not expecting it with this newer regulator.

    Kind regards,
    Daan

  • 0 in reply to Daan Pape
    TI__Mastermind 21580 points

    Hi Daan,

    I checked the lab data for the TPS62088 and can confirm the higher IQ in 100% duty cycle mode when the high side FET is turned on.

    Are you running from a battery supply? What is the max load current you require at the output?

    Best regards,

    Varun

  • 0 in reply to Varun John
    Prodigy 50 points

    Hi Varun,

    Thank you for the confirmation. If I can make a suggestion than I would add this information to the TPS62088 datasheet because the datasheet mentions the following features:

    • 4-μA operating quiescent current
    • 100% duty cycle for lowest dropout

    And there is no mention of the high quiescent current in 100% duty cycle mode. There is also no way to know it from figure 7-3 as the configured output voltage or duty cycle is not mentioned. 

    But looking forward, we only need 0.75A max in our design and this is a good fit for the TPS62840YBGR. I now ordered that regulator and I'm trying to design it in, the 0805 size for the inductor is a bit tight as we don't have much space. In the TPS62840YBGR datasheet the higher iQ in 100% dropout is mentioned in the features so I think this will be a good fit. Please correct me if I'm wrong.

    Kind regards,
    Daan

  • 0 in reply to Daan Pape
    TI__Mastermind 21580 points

    Hi Daan,

    Sorry for the confusion it caused you. I will feedback this information to my product line.

    Since your max current is low, the TPS62840 should be a good fit for your board. You can also use a smaller case size inductor if the inductance is within the recommended operating range.

    Best regards,

    Varun