Electronics > Projects, Designs, and Technical Stuff
PCM5102A: analog output level not what I expected?
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sidlauskas:
Hi,

I cannot achieve a 2.1 Vrms mentioned in their datasheet. I can only output 1.04Vrms from the 1kHz source. Do I measure it wrong or this is what I should expect? Or maybe I get such measurements because it could possibly be a counterfeit chip?

dmendesf:
Are you sure you're sending a full scale senoid to be output?
sidlauskas:

--- Quote from: dmendesf on January 27, 2019, 04:42:49 pm ---Are you sure you're sending a full scale senoid to be output?

--- End quote ---

I tried to play different sine wave tone (0 dBFS) generated from here: audiocheck.net/audiofrequencysignalgenerator_sinetone.php and now I can see 1.88 Vrms and 5.64 Vpp when there is no load. Is this something I should expect? I'm playing this sound at the full volume over bluetooth since I use CSRA64215 chip as a source for PCM5102A. I also checked CSRA64215 config and it's output level is already set to max.

SiliconWizard:
You're getting half of what is advertised in TI's datasheet. Although the latter is clear as mud.

2.1Vrms would be a +/-3V signal peak-to-peak. You're getting half of that.

From a 3.3V single analog supply, they are generating an internal positive rail and negative rail with a charge pump as I understood, so that's how you could actually get a +/-3V output.

Not sure why you're getting half of that. Maybe your input digital signal is only half of full-scale. Maybe you're loading the analog outputs too much. Maybe you're using the wrong digital format (I2S vs left-justified). Check your source code. Try changing the signal's polarity on the FMT pin.

Or lastly, the datasheet sucks and full-scale is not really 2.1Vrms but half of that. But I'd first check that you're using the right digital audio format, sounds like the most probable issue here.
SiliconWizard:

--- Quote from: sidlauskas on January 27, 2019, 07:20:26 pm ---I tried to play different sine wave tone (0 dBFS) generated from here: audiocheck.net/audiofrequencysignalgenerator_sinetone.php and now I can see 1.88 Vrms and 5.64 Vpp when there is no load. Is this something I should expect? I'm playing this sound at the full volume over bluetooth since I use CSRA64215 chip as a source for PCM5102A. I also checked CSRA64215 config and it's output level is already set to max.

--- End quote ---

The whole story is always helpful.

"When there is no load" : what do you mean? How do you load the outputs?

Also, you're apparently going from a whole chain that you probably have not much control over. What does "full volume over bluethooth" mean? What exactly is your complete signal chain? Are you using a computer or mobile, playing sound via an app through bluetooth? How can you ever guarantee bit-exact signals with that setup, if this is what you're doing? A whole lot will happen behind the scenes before your DAC receives an actual digital signal... or please show your complete signal chain in more details.


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