PCM5242: Can PCM5242 be set to 2.1Vrms in balanced output?

Alex Lee

Part Number: PCM5242
Other Parts Discussed in Thread: PCM5102A, PCM5100A

Hello

There are two questions about PCM5242. Hope anyone could help.

1. I found that there is a PCM5242 datasheet with 2.1Vrms output
https://datasheet.octopart.com/PCM5242RHBT-Texas-Instruments-datasheet-27842574.pdf

Is it obsolete?
I'd like to know if there are any ways to have 2.1Vrms since 4.2Vrms is too much for amplifier with analog volume control. There will be channel imbalances at low volumes.

2. for the LPF circuit, will this be better? The high frequency can pass to AGND and won't go through signal path.

Thank you!

8 months ago

0 Arash Loloee 8 months ago

TI__Mastermind 20830 points

Hello Alex,

The datasheet you are referring is most probably a product preview which has only 12 pages. The actual datasheet is about 130 pages-you should always use the official datasheet release as your reference. In the released datasheet, you can see that it mentions "Changed Description text in third paragraph From: "The PCM5242 provides 2.1VRMS.." To: "The PCM5242 provides 4.2VRMS." So this part is 4.2V if used differential and 2.1V if used single ended.

Please refer to section 8.7.2.1 Voltage Reference and Output Levels for more on the output levels topic. You can also use Volume control . Please refer to 8.7.3 Digital Volume Control. And finally Analog gain control can be selected between 2Vrms FS (0dB) or 1Vrms FS (-6dB). Gain is controlled via hardware by the AGNS pin, and via software (SPI/I2C), Page 1, Register 2, D4(L-ch) / D0(R-ch).

The outputs usually connected differentially to the external amplifier's input- ( after LP filter, and if you want to go single ended you can ground one of the amplifier's input while you connect DACs outputP to the other input.. Which I think it is what you are trying to show in the above diagram.

Regards,

Arash

0 Alex Lee 8 months ago in reply to Arash Loloee

Prodigy 160 points

Hello Arash

Thank you for your kindly reply!

I found that the Note about the volume control

Does it mean that it will not degrade the sound quality as usual digital volume control? (such as getting worst SNR when you lower thte volume).

Thanks again.

0 Arash Loloee 8 months ago in reply to Alex Lee

TI__Mastermind 20830 points

Hi Alex,

Referring to the block diagram of page 16 In datasheet, the note indicates the volume control is applied directly to the DAC not via embedded miniDSP .

In general many believe digital volume control hurts dynamic range performance as it reduces the amplitude before it gets to the DAC, whereas analog volume control reduces amplification and hence preserve the dynamic performance . Here is the link to a good article that you can read more about this.

Regards,

Arash