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Old 13th May 2014, 08:54 PM   #1
kinku is offline kinku  United States
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Default DIY USB isolator

I am wondering if someone look and give their opinion about this circuit for a USB isolator. It can accept external supply to power a USB DAC.
I am skipping the regulator power supply and may be use a Salas reflector to power BUS 2 side.
I am using all "through hole" components. If someone can help with finding alternatives to chokes it will be great.
For now TDK ZJY51R5-2P being considered for digital line instead of ACM4532
and power line will have BOURNS FB20022-4B ferrite beads instead of BLM21.
Since I think 5KV isolation is an overkill for audio board I am planning on using ADUM3160 which is pin to pin compatible and replaced in the circuit without any change in components.
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Last edited by kinku; 13th May 2014 at 09:31 PM.
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Old 14th May 2014, 10:26 AM   #2
maxw is offline maxw  United Kingdom
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Your C2 is quite high. To quote the LT1763 datasheet:
"A maximum value of 0.01µF can be used for reducing output voltage noise to a typical 20µVRMS over a 10Hz to 100kHz bandwidth."

But maybe you don't mind as you are not using the regulator.
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Old 14th May 2014, 11:26 AM   #3
kinku is offline kinku  United States
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That is correct,I am skipping the regulator.
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Old 14th May 2014, 02:15 PM   #4
marce is offline marce  United Kingdom
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Using SMD components would be better for this sort of design. Also are the termination resistors required for the speed you'll be using the USB at, especially if you are using PTH components, as they are going to make the layout 10 times bigger than it needs to be (increasing loop areas and possible noise pick up or radiation) never mind trying to control the 90ohms diff pair requirement for USB. PTH is realy the wrong technology for this sort of design, that should be compact.
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Old 14th May 2014, 03:10 PM   #5
kinku is offline kinku  United States
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marce problem is difficult to make a PCB for SMD with inductors.The original inductors are hard to source.
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Old 14th May 2014, 03:13 PM   #6
maxw is offline maxw  United Kingdom
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Could you design a PCB that uses alternative inductors and SMD components? They come in all shapes and sizes, SMD included. 11,000 of them at Farnell alone
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Old 14th May 2014, 03:20 PM   #7
marce is offline marce  United Kingdom
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Which inductors
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Old 14th May 2014, 03:31 PM   #8
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Quote:
Originally Posted by marce View Post
Which inductors
Maybe he means the common mode chokes...
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Old 14th May 2014, 03:42 PM   #9
kinku is offline kinku  United States
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It will be a challenging job for me,I wish someone could help. Yes it is CMC
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Old 14th May 2014, 04:13 PM   #10
marce is offline marce  United Kingdom
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ere is a nice USB common mode inductor....
http://search.murata.co.jp/Ceramy/im...0133DLW21S.pdf
used on a layout with the Adum you are using and a couple of paralleled ADUM6000ARIZ for power isolation.
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