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Extra capacitance at Tridents out?
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miero  
#1 Posted : Wednesday, October 1, 2014 8:18:00 AM(UTC)
miero

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I'm considering adding extra capacitance at output of DVCC and VDD_XO... :-/

https://drive.google.com...TmpiWGs/edit?usp=sharing
https://drive.google.com...YktoYTQ/edit?usp=sharing

Is 45uF still OK for Tridents v3.0?

But I've not tested it yet ... and I'm not sure if it will be fast enough for MHz frequencies.

Edited by user Wednesday, October 1, 2014 9:09:49 AM(UTC)  | Reason: Not specified
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avr300  
#2 Posted : Wednesday, October 1, 2014 6:48:50 PM(UTC)
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Hi Miero

What are those scope shots you're showing? Output from the tridents?

Are they "in circuit" - connected to the DAC?


I can't reproduce that.

My scope is limited to 25M. It questionable if I can see the 14M trace but I will be able to see the 2M trace.

But I can't. Nothing to be seen.

Could you be picking up EMI with the probe ? Are you using a probe tip ground clip like this: probe tip ground clip

Edited by user Wednesday, October 1, 2014 6:51:44 PM(UTC)  | Reason: Not specified
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miero  
#3 Posted : Wednesday, October 1, 2014 7:35:27 PM(UTC)
miero

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Its output from DVCC and VDD_XO Tridents mounted on B3. Output on VDD and both AVCC was clean. I was not using ground clip, but ~10cm ground lead connected to probe, but I can create one and remeasure with it tomorrow.

Same situation if B3 was connected to Leggato or completely disconected from both outputs and inputs.

I've not checked that on scope before. My 1MHz DMM (obviously) did not show anything suspicious.

EDIT: B3 is powered by ~5.1V from LCDPS.

Edited by user Wednesday, October 1, 2014 7:44:07 PM(UTC)  | Reason: Not specified
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miero  
#4 Posted : Wednesday, October 1, 2014 9:01:50 PM(UTC)
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Also measurement was similar with both 1:10 and 1:1 probe settings.
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miero  
#5 Posted : Thursday, October 2, 2014 6:44:56 AM(UTC)
miero

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I've repeated my measurements with DIY probe tip ground clip and the waveforms were the same as above.

So I've reused 47uF capacitors from the old Tridents and put them on affected outputs.

Voltages seems to be fine now.

https://drive.google.com...d3p5NUE/edit?usp=sharing
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