What would prevent the VCOM and VREF output from working in the PCM4204?

Gerry Kurz

Other Parts Discussed in Thread: PCM4204

I have some PCM4204 parts that are not working correctly.

In some cases, both the VREF+ and VCOM are at 0V, others VREF+ is 2.5V but VCOM is 0V.

I have one board out of four that is working correctly where VREF+ and VCOM are at 2.5V.

In this design, I do not have the test pin grounded as is recommended. Could this cause the problem for some parts and not for others? What is the test pin used for?

Also, at one point in the development cycle, all the parts were powered by 3.3V on the VDD while the VCC was not powered. I have subsequently fixed this problem but could the parts have been damaged by this condition?

over 10 years ago

0 Gerry Kurz over 10 years ago

Intellectual 685 points

Further information:
At power up, both VREF+ and VCOM go to 3.3V and then decay under load to 0V.

Also, grounding the test pin does not help.

0 Gerry Kurz over 10 years ago in reply to Gerry Kurz

Intellectual 685 points

I noticed that not all questions get answered in this forum.

How do I get a response?

Is there a process for filing a bug report for this part?

Any idea what I can do now?

0 Diego Melendez over 10 years ago in reply to Gerry Kurz

TI__Guru 57800 points

Hello Gerry,

Sorry for the late response, I have asked my colleague to take a look at this.

Regards,

-Diego Meléndez López
Audio Applications Engineer

0 Justin Bohr over 10 years ago in reply to Diego Melendez

TI__Mastermind 27990 points

Hi Gerry,

The VCOM port and Vref pins are not meant to supply much current if any at all, they are purely for voltage reverence. Are you buffering these pins before using the signal as a bias?

Justin

0 Gerry Kurz over 10 years ago in reply to Justin Bohr

Intellectual 685 points

Vref has only filter caps on it, and VCOM is buffered by an opamp follower.

The following is what VCOM does after power up.....

Also please note that one out of four boards is working correctly......

0 Gerry Kurz over 10 years ago in reply to Gerry Kurz

Intellectual 685 points

It appears that VCOM has some internal gating on it. What controls this gating?

0 Gerry Kurz over 10 years ago in reply to Gerry Kurz

Intellectual 685 points

So is that it?

This is the support for this issue?

What am I supposed to do now, redesign with someone else's part?

I apologize in advance for the sarcasm but asking if I am buffering is a little underwhelming in terms of support.

0 Justin Bohr over 10 years ago in reply to Gerry Kurz

TI__Mastermind 27990 points

Hi Gerry,

The VCOM pin has no digital gating behind it, it is a resistor divider from the supply rail. Could you try removing all load from the VCOM pin on non working boards and test if it exhibits the same behavior?

Justin

Audio

Audio forum

What would prevent the VCOM and VREF output from working in the PCM4204?