PCM5142: VNEG pin stuck at positive 499mV

Borge Strand-Bergesen

Part Number: PCM5142

Hi,

Problem: PCM5142 VNEG pin stuck at positive 499mV, no apparent charge pumping activity on CAPP/CAPM, no audio out.

I'm starting up a brand new design with the PCM5142 in I2C mode. Please see the attached schematic. I have made two boards. I2S lines seem to be running fine. I2C has not yet been enabled. The LDO is generating a good looking 1.8V rail. All other rails are 3.3V. Incoming I2S and MCLK look reasonable on an oscilloscope.

Please let me know what might be the cause of missing charge pumping and VNEG stuck on positive.

The schematic shows low capacitance at AVDD and CPVDD. Adding capacitance above 10µF to these nodes does not solve the problem. Neither does reducing the series resistors from 2R to 0R.

I have mounted two boards, both with the same problem.

Or do you see anything wrong on this schematic? Should I reset the DAC with I2C?

Best regards,

Børge

over 2 years ago

0 Borge Strand-Bergesen over 2 years ago

Intellectual 685 points

Also, please note that muting is disabled and that VCOM floats. Would it help to decouple or ground VCOM?

Thanks,

Børge

0 Carson Allen over 2 years ago in reply to Borge Strand-Bergesen

TI__Genius 13610 points

Hello Borge,

Our DAC expert is out of office until at least tomorrow, he will respond this week when come's back in.

Thank you for your patience,

Carson

Low Power Audio Applications Engineer

0 Arash Loloee over 2 years ago in reply to Borge Strand-Bergesen

TI__Mastermind 19320 points

Hi Borge,

Is the problems a constant problem , meaning no matter what you do, reset, power on and up you always see a 499mV at that pin ? or this value can be different?

Also I can not read any value nor details off of the schematic, may be the combination of color and size is the problem. Can you send a more readable schematic.

Thanks.

Arash

0 Borge Strand-Bergesen over 2 years ago in reply to Arash Loloee

Intellectual 685 points

Hi Arash

reset and power cycle do not help. the VNEG pin stays at positive 0.5V.

Do I need to set it up with I2C? I had some initial I2C issues which are now resolved. I can communicate with the PCM5142 but have not yet started with an init() procedure.

Please see the attached schematic for clarity.

Thanks,

Børge

0 Borge Strand-Bergesen over 2 years ago in reply to Borge Strand-Bergesen

Intellectual 685 points

DAC_section_print.pdf

0 Arash Loloee over 2 years ago in reply to Borge Strand-Bergesen

TI__Mastermind 19320 points

Thanks Borge, Thanks for sending the schematics. let me check the schematic first and will come back to you in the next couple of days.

Regards,

Arash

0 Arash Loloee over 2 years ago in reply to Arash Loloee

TI__Mastermind 19320 points

Hi Borge, I went through your schematics. I noticed you have used smaller decupling caps compared to suggested one ( but that should not contribute to the problem). Also as you pointed out you left VCOM float. What mode your are in? When in VREF mode (default), this pin ties to GND. When in VCOM mode, decoupling capacitor to GND is required.

The PCM514x also has an on-chip PLL with fractional multiplication to generate the clock frequency needed by the Charge Pump,

would you please check and verify your clocking set up is not the cause of the CP failure?

Regards,

Arash

0 Borge Strand-Bergesen over 2 years ago in reply to Arash Loloee

Intellectual 685 points

Hi Arash,

I found the error. Classical error-exists-between-keyboard-and-chair I'm afraid. During bring-up I had a lot of series resistors not yet mounted so that I could power up one thing at a time. I had forgotten to route MCLK the final stage to the DAC. With it in place it sings!

Thanks,

Børge

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PCM5142: VNEG pin stuck at positive 499mV