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We are using AFE5812 8 channel ultrasound analog front end.
All the 12 AFEs on the board were working fine for few days; but recently we observed few
discrepancies in 2 channel outputs.
One channel of an AFE had too many glitches and the data was completely corrupted.
Then for the testing purpose, the ADC was put into sync pattern mode .
The output square wave was desired to be at 19.2MHz.
We are converting this differential output into single ended inside the FPGA and we also
assigned that output to a testpoint.
When we probed at the testpoint, we observed a rapid change in the dutycycle of the square wave and the values kept changing from 40 to 60%.
Then we removed the via masking and probed at the fanout via (beneath the AFE component) of this particular channel and
observed that the P and N outputs were not 180 degree shifted but was having only a minor phase shift.
Hence the differential output was observed as glitches instead of a proper square wave.
All the other 7 channels of this AFE are working fine.
Another AFE also has one faulty channel.
When operated in the sync pattern mode, and observed in the FPGA ILA,
it showed the values FF87 instead of the desired FF00 value.
This was also routed to the testpoint and observed that the output square wave was having a dutycycle around 60%
and was also changing with time.
Then the fanout via of this channel was also probed to confirm that the issue is not with the differential to single-ended conversion in the FPGA.
The square wave was observed both on the oscilloscope as well as on the ILA.
Surprisingly , the channel output is proper when the oscilloscope probes are connected to the vias.
When the probes are removed, the output square wave becomes inconsistent.
Seemingly an added probe capacitance is doing some work in favour.
All the channels of this ADC including this one were working fine till date.
Are these 2 channel issues related to the pin contact or a faulty differential output driver of the respective channels?
Hi,
Typically for such cases, we recommend customer to do ABA swap test. We ask customer to remove the bad device and solder it to the good device position and move to good device to bad device position. If issue follows the bad device position then we can say it might be related to the device . If not then it might be due to some assembly related issue.
You must be having multiple boards. Do you see same kind of issue on multiple boards? Do you see device failing at same AFE position out of 12 AFEs across boards? If there is a same signature across boards then we need to review board layout to see any systematic pattern.
Thanks!
Regards,
Shabbir
Hi Shabbir,
Thank you for your response.
Since this is a prototype , there's only one board.
We've already replaced one AFE with a random channel issue and it worked.
The device failure is not at the same position and cannot trace a pattern.
I shall try replacing this one as well.
Ok. Thanks for confirmation. Some soldering issue also can give this kind of problem.
Thanks!
Regards,
Shabbir
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