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PCM1802: Schematic review

Stanley Ho
Prodigy 590 points

Part Number: PCM1802
Other Parts Discussed in Thread: PCM1808,

Hi Expert,

A customer is using PCM1802 as master, Vin connecting to ground via a capacitor.  When doing the I2S output test, customer found some periodic spike noise (see pictures below).   But, customer didn't find the same problem if it's PCM1808.  Could you help to review the schematic and share your experience which portion of the design may cause problem? 

PCM1802.png

 

PCM1808.png

 

PCM1802 schematic.jpg

 

Best Rdgs,

Stanley 

  • 0
    TI__Mastermind 21716 points

    Hi Stanley,

    Many older delta-sigma converters exhibit some idle tones in the noise floor which appear as spikes when a DC input is provided. When the AC signal dominates over the DC signal, these tones end up going away.

    The PCM1808 is a bit newer than the PCM1802 and likely designs this issue out, especially if the schematics are largely the same. I would drive the OSR pin to try to mitigate the issue, otherwise it could be a limitation of the old device.

    Best,

    Garret