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PCMD3140: questions about audio PDM to I2S converter with long lines

Zou Yuehua
Prodigy 30 points
Part Number: PCMD3140
Other Parts Discussed in Thread: DS90LT012A

Tool/software:

Hello TI,

I'm a new audio designer, and now I'm designing a circuit of convertering the PDM to I2S but with long lines which exceed 20 cm. I selected the PCMD3140 here and anohter two LVDS driver and receiver which are DS90LV011 and DS90LV012 respectively. The circuit of PCMD3140 designed is quit different from its typical circuit application. Because I inerted the LDVS driver and receiver into the middle of PCMD3140 and DMIC to drive a long line in my application, as below picture shows. I do not know if this circuit would work properly? And would the data from four DMICs transport to the PCMD3140 successfully? And further, would the PCMD3140 decode the PDM data stream to I2S form data successfully?

Thanks very much.

Love Cow

  • 0
    TI__Genius 9180 points

    Hi,

    Make sure that the LVDS driver can switch faster than the timing requirements for PDM with the PCMD3140, shown below:

    Make sure you use a termination resistor on the LVDS receiver. You also will want to make sure that all the lines are of similar length.

    Best,
    Mir

  • 0 in reply to Mir Jeffres
    Prodigy 30 points

    Hello Mir,

    Thanks for your replay. I selected the LVDS driver DS90LV102A here, and its switching characteristics as below shows:

    Is it fast enough for PCMD3140?

    Ok, if I use DS90LT012A, there is a the termination resistor integrated in the IC, does it mean I do not need to used such a external resistor, maybe I can place a DNP resistor in the LVDS receiver. And a paire of twisted lines may be used to transfer the LVDS data and clock.

    B/R

    Cow

  • +1 in reply to Zou Yuehua
    TI__Genius 9180 points

    Hi,

    I think this should be fine, looks like the speeds that the LVDS supports are much higher than needed for the PDM signal. I do not know much about LVDS unfortunately but you should not have problems passing 4 PDM mic signals into the PCMD3140. You can use the example script given in section 8.2.1.2.1 of the datasheet as a starting point for configuring the ADC with I2C.

    Let me know if you need more help with the ADC!

    Best,
    Mir