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Old 19th December 2006, 03:05 AM   #1
Ipanema is offline Ipanema  Malaysia
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Default PCM2707 not recognized by PC

Guys,

I've build a bus-powered PCM2707 USB board. Upon first time powered-up, my Windows XP PC detected the USB DAC and automatically installed driver for it. Funny, the second time I power ON, it give a warning message saying that my "USB Device Not Recognized". I try to restart my PC and everytime I plug in my USB DAC the same warning message pop up. May I know what causes this. FYI, I'm using the circuit suggested on PCM2707 datasheet page 29.
http://focus.ti.com/lit/ds/symlink/pcm2707.pdf

Below are the circuit that I use for board layout. Pls help me to trouble what would possibly went wrong with the design.

Thanks
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Old 20th December 2006, 01:35 AM   #2
Ipanema is offline Ipanema  Malaysia
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Measured some voltage on the board :

VDD = 3.35V (OK!)

VCCP =3.35V (OK!)

VCCR =3.35V (OK!)

VCCL=3.35V (OK!)

VBUS=5.02V (OK!)

VCOM=0.59V (datasheet meation that this should be 0.5VCCP =1.67V). (BAD!)

VOUTL and VOUTR = 0.1V (datasheet mention that this should be 0.5VCCP = 1.67V) (BAD!)

VCOM is the common voltage for DAC. I don't have a clue why this voltage is incorrect since all other voltages are at the correct value.

BTW, does VCOM voltage affect the communication between PCM2707 and PC?

Pls help!

Thanks.
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Old 21st December 2006, 04:12 PM   #3
kevinkr is offline kevinkr  United States
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Where are you getting VDO, VCCL and VCCR from? This has to come from somewhere and it wasn't clear that they are connected to anything in a quick inspection of your schematic.

VCOM is internally generated and the bad value shown indicates a serious internal problem or an external partial short.

Next I'd replace the chip. Sounds like it has been damaged. These devices are ESD sensitive so handle with care.
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