• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 30 subscribers
  • Views 412 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PCM2707 output thumping when USB is attached or disconnected and on power on and off

Andrew Welker
Intellectual 320 points
Other Parts Discussed in Thread: PCM5102A

I'm am working on a simple self-powered (not bus-powered) USB DAC using the PCM2707. While it functions correctly, I am getting a noticeable thump both when the USB is connected or disconnected and on power up/power down. Monitoring the outputs with a scope shows DC offset is the cause. The circuit, specifically the output filter and DC blocking capacitors, matches the datasheet and EVM for the PCM2707. Any idea on why this could be occurring?

Thanks for your help!

Andrew

 

  • 0
    Expert 1720 points

    Hi Andrew, if I understand correctly datasheet that on the output will be about 1.675V. In my opinion thumb can't be easily eliminated when capacitors are charged. Maybe you can try to make some external mute circuit or connect via I2S external DAC for example PCM5102A which doesn't use DC blocking capacitors and it has digital and analog mute circuit which can be also connected via voltage divider to the power supply and monitor them.

  • 0 in reply to Pavel Ruzicka
    Intellectual 320 points

    Hi Pavel,

    Thank you for your response. I would love to use a PCM5102A in addition to the PCM2707, but the project I am working on is highly cost sensitive. I'm just surprised that TI's own EVM for this part does not have any muting circuitry. It would be very uncomfortable to plug and unplug the USB cable with the EVM connected to a large amplifier and speakers! Unfortunately the muting circuit solution is not so simple because it must act on both power up/down while a USB cable is connected (the way most consumers would have it setup) and also when the DAC is powered and the USB is plugged in or unplugged. Both conditions, as you correctly point out, result in a fairly high DC offset swing as the DAC outputs go into or come out of being set to BPZ (bipolar zero, 1.65V). It's unfortunate that TI did not think to give us a status output that is appropriately timed to drive a muting circuit. I had originally thought to use the suspend output, but it's it actually timed backwards to what's required and the thumping is still present. Does anyone have any solutions to this problem, or maybe suggest a different USB1.1 DAC?

    Thanks.