I am using the AD7685 in CS mode 3-wire with busy indicator. I have Vref and VDD tied to 5V (with caps as recommended), and VIO tied to 3.3V. SDI is tied to 3.3V also, and SDO has a 47.5k pullup to 3.3V.
The sclk is about 1MHz, with CNV pulsing every 20us or so.
On IN+ there is 3.79V, and IN- has 1.27V, for a differential input voltage of 2.52V. I would expect this to be around 0x8106 on sdo output, but instead the output is 0x55BB.
Why isn't the output code matching the values in table 8. of the datasheet?
The AD7687 is available for purchase / sampling on the analog.com website in the MSOP and LFCSP package. Here is a link: http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7687/products/inventory.html
As well, I noticed it is available on some of the major electronics distributor web sites.
On top of the AD7687, you could consider the AD7688 or the AD7693.