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PCM1754-Q1: Audio forum

yoshiki hasebe
Mastermind 6385 points
Part Number: PCM1754-Q1
Other Parts Discussed in Thread: PCM1753

Dear Sirs,

My customer asked us about pin capacitance specification for PCM1753 and PAM1754.

1.Does the PCM1753 / 54 have SPECification of the output load capacitance of the VCOM pin?

  So I checked e2e then I found as below.

 https://e2e.ti.com/support/audio/f/6/t/721055?tisearch=e2e-quicksearch&keymatch=pcm1754-Q1

The VCOM values is generated by a resistor divider created by two 42kΩ resistors. That can be used to calculate the tau of about 420ms.

I found the following answer in it.
So, is “τ = 420 ms” a Specification?
Is this maximum?

Please let me know if you have it.

２．Does the PCM1753 / 54 have SPECification of the input capacitance of the SCLK pin?

Please let me know if you have it.

Best Regards,

Y.Hasebe

  • 0
    TI__Guru 53993 points
    Hello Hasebe-san,

    The PCM175x-Q1 does not have a specified requirement for the capacitance on the VCOM pin. VCOM is a just the voltage reference created to bias the output of the PCM, and it is created internally with a voltage divider created by two 42kΩ resistors. The problem with this architecture is that noise on the power supply is also present on the output of the PCM (attenuated by 50% due to the divider). For this reason, we recommend placing a capacitor on the VCOM pin to form an RC filter to remove some of the power supply noise. A larger value will have a lower fC and improve noise performance, but it will require a longer time reach the VCC/2 value.

    The balance of these two items can be determined by the application, but generally a value around 2.2µF should suffice.

    We have not specified the input capacitance of the SCK pin. In general, I recommend a small series resistance on the pin to isolate capacitance. Usually a value from 10Ω-33Ω is acceptable.

    Thanks,
    Paul
  • 0 in reply to Paul_Frost
    Mastermind 6385 points

    Hello Paul-san,

    Thank you for your reply.

    I understand your comments.

    I will explain them to my customer.

    Best Regards,

    Y.Hasebe