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Original question:

TPS73801-SEP: TPS73801 simulation model

TPS73801-SEP: Output impedance peaking

Bryce Hesterman
Prodigy 20 points
Part Number: TPS73801-SEP

Tool/software:

The AC model of the TPS73801-SEP shows peaking in the output impedance when a modulated load current is applied.  Does the part actually behave like this? 

  • 0
    TI__Genius 12010 points

    Hi Bryce,

    I don't have output impedance data on hand to directly compare against. However, based on experience with previous measurements I will say it is important to consider the output impedance of the output capacitor as well and make sure the system is modeled fully. I see for now your schematic has an ideal capacitor - if you're able to locate the vendor's impedance SPICE model for the cap you plan to use then I would expect a more realistic result. Even adding a series resistor for the ESR should help.

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 20 points

    I added a vendor capacitor model.  This LDO is advertised as being stable with a ceramic output capacitor, so I modeled it with that type.  The resonant peak is only 4mV lower than the ideal capacitor. I have simulated other LDOs that don't show the resonance, I'm interested to see if this is how the part actually behaves. I may be able to test one of these, but they are over $200 each.

  • 0 in reply to Bryce Hesterman
    TI__Genius 12010 points

    Hi Bryce,

    Thanks for the additional detail. While I can't speak to the output impedance specifically, I can say from my experience with feedback injection stability bode plots that this part generally benefits from higher ESR if smaller capacitances are used. Your plot would seem to agree, and the bode plots produced by this model generally align well with bench. 

    Thanks,

    Sarah