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AD7616 REFCAP pin doesn't output 4V

Question asked by Kristof_Mulier on Apr 20, 2017
Latest reply on Jul 16, 2017 by Kristof_Mulier

I have designed a board with an AD7616 chip on, connected to a microcontroller. The AD7616 chip is configured in software mode and with SPI interface (one MISO and one MOSI wire). I have read the whole datasheet, and believe that the connections are okay. This is my schematic:


AD7616 connections


These are my findings:


1. SPI doesn't function

The first problem I encounter is the nonfunctional SPI connection. I attempt to write the CONFIGURATION_REG at address 0b00010, and read it out again to verify if the value really changed. I read out only zeros. The MISO pin (master in, slave out) remains low.

In short - the SPI connection doesn't work. I've checked the signals with my oscilloscope. The microcontroller outputs the expected waveforms. The AD7616 remains dead.


2. All power supplies are connected

I have checked the presence of 3.3V and 5V on all the power-pins of the AD7616. The power supplies to the chip are okay. So the problem is not related to wrong or missing power levels.


3. No voltage on the REFCAP pin

All the following pins should have a specific voltage: REFCAP, REFINOUT, REGCAPD and REGCAP. They are all okay, except REFCAP. This pin should output 4.096V, but I don't measure any voltage.


What could be wrong?


PS: I have added the full schematic figure to this post. See file AD7616_problem.png.


EDIT: I got the chip eventually working. You can find the answer on Stackoverflow here: adc - AD7616 REFCAP pin doesn't output 4V - Electrical Engineering Stack Exchange