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PCM1754-Q1: FMT pin does not work

Part Number: PCM1754-Q1
Other Parts Discussed in Thread: PCM1753-Q1, PCM1754, PCM1753,

Hi Expert,

We are getting a problem with this hardware control IC and getting too much distortion over audio because of format mismatch, we have pulled down the FMT pin using a 100 Ohm resistor to get a 24-bit I2S format. From the laptop, we have selected 24-bit 44.1 kHz format. At scope, the waveform of LRCK and BCK, we get the right frequencies 44.1 KHz and 2.822 MHz respectively as per the datasheet.

Previously, we were using PCM1753-Q1, we had configured SPI from software to set format 24-bit 44.1 kHz and successfully play audio without distortion.

Please correct me if I am doing the wrong configuration.

Thanks,

Mohit

  • Hi Mohit,

    Once you set the FMT it should be all needed for PCM1754.

    You can send a 1KHz sinewave and check the following pins SCK, BCK and fs and specially  the Din waveform edges.  Please share the screen shot of these signals

    Most probably you are setting the FMT to be 24B I2S  correctly on the IC  but data sent is not I2S, maybe it is right justified. So please concentrate on the clks waveform and see if it matches Fig23 part2.

    Regards,

    Arash

  • Hi Arash,

    At scope, we are getting left justified 24-bit data but I won't confirm whether it is I2S or not. The clocks waveform looks ok to me. We are not in a good position to capture those images, sorry for that.

  • Hi Mohit,

    PCM1754 is a very simple hardware control device  and in almost all cases  I have seen , either  wrong clocks or wrong input format has been the case.

    FMT=low puts the device in I2S mode . From your description you already confirmed the clocks are ok but sending left justified input.  Please see the format comparison table for PCM1753 vs PCM1754

    The PCM1753-Q1 device supports industry-standard audio data formats, including right-justified, I2S, and left justified. The PCM1754-Q1 device supports I2S and 16-bit-word right-justified audio data formats.

    You need to send the correct format to the Chip as indicated above.

    Regards,

    Arash

  • Hi Arash,
    Sending the wrong clocks is not in our control because those data and clocks are sent by laptop HDMI out. We can control only SCK and the data format of I2S from the laptop. Only configuration can be changed from hardware FMT pin. I tried FMT to one time low and high but didn't get results.

  • In above waveform, yellow is data, blue is LRCK, so according to waveforms, input data visible format is I2S that goes to DAC.

  • Mohit, PCM1754 doesn't work with LEFT justified, However  PCM1753 WORKS as I showed in the above screenshot of datasheet.

    You already confirmed you are sending LEFT justified format at the input.

    In general you always need too see BCLK along with LRCLK and DIN to see the format, something that is missing in your screenshot.

    Regards,

    Arash