PCM1804: VcomR and VcomL join in case of unbalanced connection

Jar Grb

Part Number: PCM1804
Other Parts Discussed in Thread: PCM1802

Tool/software:

I need to connect battery powered amp to PCM1804. But I have one op amp only.

I want to connect Vcom to amp GND to lift it to 2.5V. That works well with PCM1802. But PCM1804 got independent Vcom for L and R channels. Is there any issues connecting VcomL and VcomR together? If you can share piece of internal input structure it will help much.

6 months ago

0 Jeff McPherson 6 months ago

TI__Mastermind 46805 points

Hi,

I would not join them together. Rather use VcomL for the left amplifier and VcomR for the right amplifier. The two Vcoms will probably not be exactly the same and so I would keep them independent, since the microphone channels will be independent anyway with their own amplifier.

Best regards,
Jeff McPherson

0 Jar Grb 6 months ago in reply to Jeff McPherson

Prodigy 30 points

Unfortunately that is the problem. Microphone channels got one battery and so got one ground. So both channels share same ground. I can't separate it. I tested this solution, it works, but I can't see any S/N improvement over PCM1802. So I need to know if I loosing so much S/N with this connection?

0 Jeff McPherson 6 months ago in reply to Jar Grb

TI__Mastermind 46805 points

Hi,

Sharing ground shouldn't be a problem. The VCOM should be applied to the non-inverting side of the preamp in order to set the reference. See the application diagram below:

Best regards,
Jeff McPherson

0 Jar Grb 6 months ago in reply to Jeff McPherson

Prodigy 30 points

Thanks for your help. But I have no room for additional op amps. Ok, I will look for an other ADC with one common pin.

0 Jeff McPherson 6 months ago in reply to Jar Grb

TI__Mastermind 46805 points

Hi Jar,

The diagram is just a reference. Even with one op amp per mic, the point is that the VCOM of each side drives the non inverting terminal of the op amp, creating the bias.

Best regards,
Jeff McPherson

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PCM1804: VcomR and VcomL join in case of unbalanced connection