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TPS7A7001 Maximum allowed output capacitance

mwikman
Prodigy 70 points
Other Parts Discussed in Thread: TPS7A7001, TPS7A7200

Hi,

The datasheet mentions in Recommended operating conditions that maximum output capacitor is 47uF but in Figure 2 illustrates regulator stability using Cout =100uF. 

It is possible to operate the TPS7A7001 with an even larger Cout than this? We need to add extra output capacitance somewhere between 600uF and 1000uF. Is this possible with TPS7A7001? If not, is there any hack that can be applied between the regulator and the capacitor to allow larger output capacitance?

Best regards,

  • 0
    TI__Guru 55940 points
    Hi Marten,

    1000uF is an extreme amount of capacitance! The inrush current caused by this capacitor will challenge any LDO.

    We recommend the maximum output capacitor of 47uF in order to limit the inrush current for stability purposes during startup.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 70 points
    Thank you Ryan.

    What about changing to a LDO that has soft-start? For example TPS7A7200 has a configurable soft-start delay that would limit the inrush current. Would this regulator be able to manage a output capacitance of 1000uF if SS-pin is properly configured?
  • 0 in reply to mwikman
    TI__Guru 55940 points

    Hi Marten,

    A soft-start delay does help limit inrush; however, please note that in the Output Capacitor Requirements section for TPS7A7200 we again have 47uF as the largest capacitor that we recommend for stability.

    Here is an Application Report that does discus some techniques to add/increase softstart capability: 

    1000uF is well outside of the range that we characterize our LDOs.  

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 70 points
    Thank you Ryan.

    I guess the proper way to fix this is to add the capacitance before the regulator and not after.