calibrating CS5460A - unstable voltage and current values

[pawelj]

Hi,

I have a breakup board with CS5460A connected to an Arduino.
The sketch and library is taken out of the github repo https://github.com/xxzl0130/CS5460.git
The communication is working, expected values can be read from configuration registers after reset.
Something what I don't understand are voltage and current values I am getting out of Instantaneous Voltage and
Current Registers.
The values are fluctuating even though inputs are shorted and connected to VA-.
Here are some values:

000F0A
000D2A
0004E2
00014A
000EE2
00140A
FFFABA
FFFA92
00082A
FFFC22
000172
FFFC4A
000672
000302
FFEEDA
FFF1FA

This looks like maximum 10 bits of usable values and 14 bits of noise.
Is what I observe normal?


The things which I tried so far to get more stable readings:
- use separate linear (7805) power supply.
There is one 7805 for VD+ and one for VA+. The 10ohm resistor on the breakout board is taken out.
Arduino board is still powered up with USB
- check frequency stability of CPUCLK
- Invert the CPUCLK clock using iCPU bit in configuration register
- use different arduino board (uno -> leonardo)
- lower clock for SPI from 2MHz to 1MHz
- use single measurement mode to keep SPI quiet during sampling


Unfortunately I have no second CS5460 to swap it.

Cheers
--pawel