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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


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.

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

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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!

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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.
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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