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TPS7H4010-SEP: Questions about Cff calculations - value and pole/zero frequencies

Jim Brinkhurst1
Mastermind 44680 points
Part Number: TPS7H4010-SEP

Hi expert

I have some questions about the Cff value on the EVM, and the pole/zero values that go along with it. 

When I use datasheet Eq 21 I get 59.4pF for Cff based on the other EVM values and using Fx = 48.8 kHz (per the EVM specs of 3.3V output, 150uF Cout and K = 24.16)

I think this value of Cff makes sense given I'm using Fx = 48.8 kHz, and in this other post you had used 10 kHz. (e2e.ti.com/.../tps7h4010-sep-cff-calculation-guidance

For 59.4pF the corresponding zero and pole frequencies I calculate are:

Fz-Cff = 26.8 kHz

Fp-Cff = 1.156 GHz

Are these zero and pole frequencies reasonable, given the intent of Cff?

Thanks for your help.

Best regards,

Jim B 

  • 0
    TI__Mastermind 28455 points

    Hey Jim,

    These are the equations for the pole/zero locations:

    R1 being the top resistor and R2 being the bottom.

    This gives ~24 kHz for the zero and ~80 kHz for the pole (R1 = 100 kOhms and R2 = 43.2 kOhms)

    The pole/zero locations should have a geometric mean around the crossover frequency.
    My numbers here give ~44 kHz

    Thanks,
    Daniel

  • 0 in reply to Daniel Hartung
    TI__Mastermind 44680 points

    Thanks Daniel

    Your equations above helped me identify an error in equation 20 in the datasheet.

    Equation 20 has Rfbt / Rfbb, but should have Rfbt // Rfbb.  Can you get this correction in queue?

    Instead of showing the // symbol we could update equations 20 and 21 to show the actual parallel calculation details. This might avoid confusion for folks who aren't familiar with the // notation, or who just miss it when reading the equation.

    Best regards,

    Jim B

  • +1 in reply to Jim Brinkhurst1
    TI__Mastermind 28455 points

    Hey Jim,

    Thank you for the note.
    Ill work internally on corrections.

    Thanks,
    Daniel