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TPS62067-Q1: TPS62067-Q1: Stability question

Part Number: TPS62067-Q1
Other Parts Discussed in Thread: TPS62090-Q1, TPS62065-Q1

Dear *,

I have some questions regarding the stability of TPS62067-Q1:

First this is my configuration:

Iout is from 100mA to 350mA

1) What is the impact of the capacitance that is after Ferrite bead on DCDC stability ?

2) Is there a way to calculate the cff without to measure the crossover frequency?

3)Does the Equation 6 on page 14 in DS apply also to PFM mode?

Best Regards.

  • Generally, the ferrite bead has minimal stability impact and the capacitance following the bead should just be summed with the capacitance on the output. Per the D/S, you have too much Cout which may not be fully stable.

    This app note explains how to estimate phase margin without a bode plot: But best is to use the bode plot.

    Equation 6 is mainly for PWM mode--it is the textbook ripple current calculation.

    In your schematic, C3 needs to connect to GND.

    The TPS62090-Q1 supports higher Cout.
  • Dear Chris,

    maybe you know is there a document or a calculation how the ferrite bead impacts the stability?

    Is there a ripple current calculation equation for PFM mode?

    Best Regards.
  • I'm not aware of any calculations. You can use the spice models on the product page. But best is to measure the behavior on an EVM.

    As well, for most automotive applications, forced PWM mode (with the TPS62065-Q1) is used for lower noise.