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TPS62136: TPS62136 output capacitance

Craig MacKinnon
Prodigy 90 points
Part Number: TPS62136

Hello TI

The data sheet for the TPS62136 suggests that in order for the voltage output to be stable the total ESR of the cap bank can't get too low. For a power rail capacitance of >= 400 uF, it is recommended that that the trace ESR be a minimum of 10 milli-Ohms in order to ensure sufficient ripple for the output to stay in regulation. If we can't guarantee that the trace series resistance will be > 10 milli-Ohms is it sufficient to use a capacitor (say tantalum/tantalum-poly dielectric) with a higher ESR directly on the output of the convertor before the voltage gets distributed to the DDR4 power rail to keep the voltage in regulation? 

cheers,

Craig MacKinnon

Christie Digital Systems

Kitchener, ON



  • 0
    TI__Expert 3350 points

    Hi Craig,

    Yes, you can use a higher ESR tantalum dielectric capacitor on the output of the converter. You can follow up by checking the load transient and bode plot as well to ensure the design is stable and works as expected. 

    Best,

    Emily

  • 0 in reply to Emily Kong1
    Prodigy 90 points

    Hi Emily

    Thanks for the prompt response. One more question I should have asked in my original post:

    Are you able to tell me what the minimum peak to peak ripple voltage is that the feedback loop needs to see in order for the loop to be stable?

    cheers,

    Craig MacKinnon

  • 0 in reply to Craig MacKinnon
    TI__Expert 3350 points

    Hi Craig,

    There is no such minimum spec on ripple. To ensure stability, a design needs to have a certain range of output capacitance for a given inductor. If the output capacitance is too high, there needs to be enough damping to make sure the Q factor of the LC filter is not too high. If the concern is having the appropriate amount of trace resistance for multiple loads, section 10.3.2 of the datasheet contains a system example for ensuring a sufficient trace resistance. 

    Best,

    Emily