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Old 20th April 2006, 06:30 AM   #1
Ipanema is offline Ipanema  Malaysia
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Default PCM2707 Problem

Hi,

I've build PCM2707 according to datasheet. Upon power-up, windows detected new USB device but can't recognize it and also no driver is assigned to it. Does Windows XP suppose to autodetect it and replaces my internal soundcard as sound output device? FYI, I'm using Windows XP Profesional and my soundcard is internal build in type. What shall I check/do to ensure that it is working properly?

here is my schematic and layout. Pls help
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Old 20th April 2006, 06:31 AM   #2
Ipanema is offline Ipanema  Malaysia
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schematic
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Old 20th April 2006, 07:04 AM   #3
Ipanema is offline Ipanema  Malaysia
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schematic
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Old 20th April 2006, 07:47 AM   #4
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How did you power it up? If you apply power to the 5V rail that D+ is pulled up to before plugging in the usb jack, you can burn up the chip.

Without seeing a pic of your board, that would be my first guess. My second guess would be the obvious -- check for solder bridges, cold joints, etc.
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Old 20th April 2006, 01:57 PM   #5
Ipanema is offline Ipanema  Malaysia
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oh no. I did just that. How to confirm that my chip had burned? i've check the solder point, all pin are connected properly.

There is no warning in the datasheet to ask not to power up without plug into USB port.
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Old 20th April 2006, 02:02 PM   #6
Ipanema is offline Ipanema  Malaysia
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My mistake, didn't check the fine print :

"D+ must not activate (HIGH: 3.3 V) while the device is detached from the USB"
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Old 20th April 2006, 04:46 PM   #7
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I don't know if there is a good way to tell if the chip has died. The best thing, I guess, is to triple check all of the connections and if everything else looks fine, replace it and see what happens. There is a thread over at head-fi where we did some explorations on how to remove this chip without damaging the board. The winning method was to use an x-acto knife to (carefully!) cut each pin to remove the chip, then to use a soldering iron and tweezers to remove the pins.

For your next build, the clever method for preventing problems is to use an AND gate so that you don't power the connection unless both the external power and the usb jack are connected.

-d
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Old 20th April 2006, 07:56 PM   #8
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Quote:
use an AND gate so that you don't power the connection unless both the external power and the usb jack are connected
dsavitsk,

This is just what I'm looking for before I modify my USB DAC to self power but I'm dumb - any chance of a quick schematic?

Instead of running 5V to Vbus and allowing the 2706 chip internal regulator to provide 3.3V to appropriate pins - has anybody tried to fully self power by providing an externally regulated 5V to Vbus & 3.3V to appropriate pins Vccp, Vccr, Vccl & Vdd.

Does this make a sonic difference?

John
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Old 20th April 2006, 08:31 PM   #9
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You can also use a 74hc08, but you'll have a bunch of exta pins.
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Old 20th April 2006, 10:37 PM   #10
jkeny is offline jkeny  Ireland
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Thanks dsavitsk

So this works by sensing when 5V is found on A & B it will send 5V out of Y pin to D+ (should this not be 5V out to Vbus pin on PCM2707?)

John
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