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PCM1808: BCK and LRCK flow into the device at OFF state

Eng Lih Khaw
Expert 2000 points
Part Number: PCM1808

Hi,

I would like to ask a question for PCM1808 ADC.

Would it be a problem if there is continous LRCK and BCK input to PCM1808 (from DSP) when the device VDD/VCC are OFF?

We observed that when there are no VCC or VDD to the PCM1808, but the LRCK or BCK signals keep HIGH from DSP, it will rise the VDD of PCM1808 to around 2.2V.

 

Looking forward for your favourable response.

Thanks

  • 0
    TI__Guru 57800 points

    HI, Eng Lih,

    It seems the voltage you are getting in the digital power supply (VDD) is leaked from the I²S lines. This situation might not cause a failure to the device but is not a recommended operation. Probably the best would be to gate the I²S lines provided to the PCM1808 until both power supplies (or even just VDD) are stable.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Expert 2000 points

    Hi,

    Thanks for your advise

    Can you advise why it could leak to the VDD? Is it possible to help me understand if there's any connection between I2S and VDD internally?

    Thanks

  • 0 in reply to Eng Lih Khaw
    TI__Guru 57800 points

    Hi, Eng Lih,

    Unfortunately, we don't have performance or test data for an application like this where I²S voltage is leaked to VDD as providing I²S lines without power supplies is not a recommended operation mode. The internal connection is related to the Audio Serial Interface architecture, but this information cannot be disclosed. 

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer