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TPS7H1101A-SP: Maximum Output Capacitance ESR

Part Number: TPS7H1101A-SP

The datasheet states a maximum recommend output capacitor ESR of 1 ohm. Is this ESR specified at DC or the resonant frequency of the capacitor?

In my case, program requirements prevent us from using the recommended capacitors in Table 8-2 of the datasheet. The 22uF capacitor from the product family we have baselined can be as high as 9 ohms at DC according to the manufacturers provided data:

https://spicat.kyocera-avx.com/product/tan/chartview/TAZG226J020CWLB9

Will this cause stability issues with this regulator?

  • Ryan,

    Some manufacturers describe the nominal ESR differently.   I am uncertain on what was intended when the 1 ohm was defined as the max.   I suspect it is at 100kHz.  

    Please let me research and check with our design team to see if I can further clarify.

    The capacitor's worst case ESR exceeds 1 ohm within the loop bandwidth of the LDO.  I suspect this cap will not be sufficiently stable.

    I will reply back after getting some additional feedback.  This may take several days.

    Regards,

    Wade

  • Hi Wade, 

    Thanks for looking into this. Unfortunately, our ceramic capacitors have similar ESR as the tantalum linked above:

    Is it possible to compensate the regulator to maintain stability for this high of an ESR?
     
  • Ryan,

    Please let me have a few more days to obtain input from the design team.   I will respond back early next week.

    Regards,

    Wade

  • Ryan,

    I was able to locate a little bit of data.  Unfortunately, it does not indicate the source of setting the 1ohm limit for ESR.

    The responsible designer is currently on travel this week, so I am not able to get additional insight immediately.

    However, it may be viable to parallel multiple 6.8uFs and/or the 22uF tantalum to get a lower effective ESR.

    I will still push to get additional data from the design team.  However, this will push into next week based on current schedules.

    Regards,

    Wade

  • Ryan,

    The feedback I have received essentially indicates that the 1 ohm ESR recommended max limit was chose to bound the evaluation to some degree.  It is not saying that larger ESRs will not work, but that the efforts to bound stability with larger ESRs was not performed or simulated.

    Using multiple of your 22uF's in parallel should bring the effective ESR down.

    The WCA model can be used to estimate the frequency response with chosen configuration.

    We do have an EVM for this device.  Unfortunately, it was not created to properly test stability.   It requires modification to the board in order to test.  I do have in my queue to redesign this board.  However, this will not be complete or released until later this year.

    Regards,

    Wade

  • Hi Wade, 

    Thank you for following up on this. I have downloaded the WCA model and will use that to test multiple output capacitors in parallel.