I have used AD7768 on my design. For some unknown reasone, when I make a first power on, the ADC blown out and the AVDDx pins become a low input impedance.
What are the supply voltages that you are using? Are you able to share the schematic for your board?
Have you checked for shorts on the board? The AVSS and DGND pins must be connected before the board is powered up. All analog inputs, digital inputs and the reference should not be applied until the part has been powered up first
The AVDD1 and AVDD2 are tied together from the same 5V. The DGND and AGND are tied together just beneath the ADC footprint.
We followed the power sequence as the Dev kit, 5V first, 1.8V next and Reference and analog input.
Fan Liu | Sr. Engineer
250 CrossKeys Office Park, Suite 285
Fairport, NY 14450
(585) 419-9576 | email@example.com<mailto:firstname.lastname@example.org>
www.vanteon.com<http://www.vanteon.com/> - Electronic Design
Could you share a section of your schematic to show the other connections to the ADC pins and the decoupling used?
For 1.8V IOVDD operation have you tied IOVDD to DREGCAP?
For 1.8V IOVDD, as the schematic shown, we tied IOVDD with DREGCAP together.
I am a little bit confused, which part of the schematic do you want?
Would you be able to share at least the AD7768 portion of your schematic so that we can rule out that section as a source of the problem.
Do you see this issue on multiple boards and multiple devices or is it just one board?
Would you be able to share scope shots of the power on sequence?
Please see file attached.
In the schematic, RegCap pins are tied to 5V. These are LDO outputs. These should be decoupled to AVSS using 1uF capacitors.
I found the problems.
It was our fault on rework.
The case can be closed.
Thank you very much.
Retrieving data ...