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TPS74801: Bode plot measurement

user4979989
Intellectual 2800 points
Part Number: TPS74801

Hi team,

For TPS74801 or general LDO product, is bode plot measurement needed to make sure the stability?

If yes, how can we fine tune TPS74801 if the gain/phase margin is not enough?

If not, how can we check the system is stable? by transient/static?

Thank you.

  • 0
    TI__Genius 10490 points
    Hi,

    You do not need to measure the bode plot to ensure an LDO is stable. Stability can be determined by measuring the LDO output voltage transient in response to a load step. The output voltage will settle if the LDO is stable, typically after some ringing. This application report explains in detail how transient ringing relates to a regulator's phase margin:

    www.ti.com/.../slva381b.pdf

    The TPS74801 is designed to be stable with any output capacitor larger than 2.2 uF. If you find the load transient response is not sufficient for your application you can increase the output capacitor or use one with a lower ESR. X5R and X7R ceramic capacitors are generally recommended due to their low ESR and minimal variation over temperature. LDO stability can also be improved by adding a feed-forward capacitor in parallel with the top feedback resistor. There is more information about the advantages and disadvantages of using a feed-forward capacitor in this application report:

    www.ti.com/.../sbva042.pdf

    Thanks,
    Gerard