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AD7663 doesn't work in a custom board

Question asked by relkin on Sep 20, 2015
Latest reply on Oct 17, 2015 by relkin

Hello,

 

I made an ADC circuit (with USB interface) for radiation spectrometry using schematics and layout of eval-ad766x as a hint. I use a FPGA circuit as a digital logic. Before AD7663 there are some additional analogue circuits, which regulate level of input signals and track&hold them. I don't use any cores to communicate  FPGA with ADC - I made simple shift register.

 

I wanted to use AD7663 in slave serial interface mode, but I didn't get BUSY signal from ADC, so I checked other modes (master serial, parallel). There was no BUSY signal or clock from ADC (in master mode), and in parallel mode I didn't get even LSB bouncing. I checked soldering, footprint, AVDD (~5.2 V), DVDD (~5.2 V), OVDD (3.3 V), grounding, reference (2.5 V), clock (ext. 40 MHz or 20 MHz in slave mode), reset, pins configuration (configured by 3.3 V signals from FPGA, 3.3 V supply using 4k7 resistors or GND). Finally, I changed AD7663 to new one and it works the same way (no BUSY signal, no communication). What could be wrong?

 

I attached schematics of ADC part of my circuit.

 

Any comments are welcome.

 

Thanks!

 

adc_usb_adc_part.png

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