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AD7175-2 not able to read ID register reliably

Question asked by vdevram on Feb 22, 2017
Latest reply on Mar 9, 2017 by JellenieR

Greetings,
I am using an analog devices EVAL-AD7175-2SDZ board to evaluate AD7175-2, and
I am not able to read the ID register consistently. It sometimes gives me the answer, and sometime it does not.
I am using the no-os master drivers, and connecting to a microcontroller board SPI via header A7.

 

Please help me resolve this issue, it is blocking us from using this ADC.

 

Details:
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1) I am connecting it to a cypress PSOC microccontroller board via the header A7.
2) I have made the changes for EVAL-AD7175-2SDZ to operate the board at 5v

3) The SPI logic levels are at 5v, as verified on the scope (please see attached pictures).
In the attached scope pictures, yellow = SPI clk, blue = SPI MOSI, purple = SPI MISO, green = CS.
I am in SPI mode 3 in teh master (CPHA=1, CPOL=1), clock speed is 100kbps.

4) The read ID register command looks okay, as seen on the scope MOSI line(hex value 0x47 is being written to the commmand
register)

5) The issue is: sometimes I see the chip returing the ID value, and sometimes it does not.

6) Also, an unrelated observation: the dout/rdy pin is being pulsed at some varying frequencies (sometimes higher, some).

7) I have also tried the following to no success:
- Resetting the chip multiple types (holding DIN high for 64 clock cycles). I do not see any difference.
- Tying CS low (that is, tying CS to ground). This does not work. Chip never responds in this scenario.

Regards
Vishnu

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