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TPA3255EVM: The voltage gain is changed by input frequency in tpa3255evm

Minho Sohn
Prodigy 50 points
Part Number: TPA3255EVM
Other Parts Discussed in Thread: TPA3255

Hi,

I' am using TPA3255EVM for testing a piezo actuator driving.

the detailed driving conditions are  described as below

- load : piezo actuator, 200nf

- driving frequency 20k ~ 40khz

- driving voltage 50Vpp ~100Vpp, with a pure sine wave, BTL driving

[question]

1. The Voltage gain by driving frequency is changed by the input frequency of sinewaves

  - When i test under 20khz, the voltage gain is about 21.5dB as tpa3255 datasheet.

- but when i drive over 20khz(i.e. 30khz), the voltage gain over 25dB

-when i drive as 40khz, the voltage gain is about 30dB.

-Is it normal? Could this be a something like an oscillation?

-If so, what component  on the 3255EVM do i need to modify?

Thank you in advance.

  • +1
    TI__Expert 5170 points

    Hi Minho.

    Minho Sohn said:
    -Is it normal? Could this be a something like an oscillation?

    This is related to the output filter of the EVM and the capacitance of the piezo.

    Minho Sohn said:
    -If so, what component  on the 3255EVM do i need to modify?

    You can download the LC filter calculate tool to choose LC filters that can satisfy your requirement.

    LCFILTER-CALC-TOOL Design tool | TI.com

    PS: Because you connected a piezo load, the value of C in the output filter is equal to Cout+2*Cpiezo, and because there is no resistive load, the resistive load in the table needs to be set to a larger value.

    BR.

    Wei Qiu.