Help needed with PCM2706

[appleby]

Hi,

I built the circuit at page 29 of PCM2706 datasheet:

focus.ti.com/lit/ds/symlink/pcm2707.pdf

It doesn't work. When I connect the USB cable to PC (Windows XP) it says "UNKNOWN DEVICE".
I also notice that the 12 MHz crystal oscillator doesn't work (I use CMAC HC49 12.000).
I don't know what to do.

Thanks for your help

 

[dddac]

If the oscilator does not work, the device will NOT be recognized by Windows, so fix that first ....

doede

 

[gfiandy]

Have you pulled the suspend pin high, if not the circuit will not start up. Also check the circuit arround the clock oscillator to make sure it has not got any shorts and is wired correctly the oscillator should start even if the part is not running correctly. Also check the power supply is good and is getting to all the power pins.

Regards,
Andrew

 

[appleby]

Thanks for suggestions!

I check the circuit and it seems to be ok.

I pulled up the suspend pin too, but I obtain the same Windows message.

I will do more attempts and I'll see.

Thank You all!

 

[jaycee]

See my own PCM2607 design here

I think that the PCM2606 has to have a programmed serial EEPROM connected to it, containing the USB identification data. The PCM2607 does not.

Check the chip is generating 3.3v on the VDD pin. Note how the USB D+ line needs to be pulled up with this 3.3v. I am assuming you are using bus-powered here.

edit: Hey, I just noticed I didn't pull *SSPND high! Whoops, oh well, my circuit still works.... it is probably internally pulled up.

 

[appleby]

I think that PCM2706 works without the EEPROM too.

I make some measurement and I think my problem is that the oscillator doesn't start.
I measured 3.3 V on pin 13 (XTO) and 1.8 V on pin 12 (XTI) but I didn't see any oscillation.

Thanks for replies.

 

[jaycee]

I would say that you need to mess about with the values of C1 and C2. The data sheet for your xtal should recommend values for these.