why my collection of ADS8860‘s data like this

Hi,

An ADC will have a DC code spread for a given analog input voltage. Please refer to Figure 14 and Figure 15 on Page 11 of ADS8860 datasheet. 

Hi thanks for your replay,I setted Vref as 3.3V the same with AVDD ,is that right and if that whitch Figure should I refer to ?

Vref should be driven with a low noise and low output impedance driver.

As shown in datasheet, you could use the composite amplifier recommended on Page 33. You could also use REF6033 which is a low noise voltage reference with an integrated reference buffer.

Hi RahuIVK，
here is my ADS8860's  CONVST,DOUT,SCLK and SDI observed in logic analyzer

channel 0 is CONVST，channel1 is Dout, channel 2 is SCLK,channel is SDI. Is there any problem?In  addition  SCLK is about 2MHz.

Hi Ruan,

The signals seem fine.
As there is no time scale, you need to ensure that CONVST is held high for 710 ns i.e. conversion time max.

Is there some specific issue you are facing?

Regards,
Rahul

CONVST must keep high for 710ns? I set the time for 680ns as the datasheet said 500-710ns.
my quesetion is that I set the analog input half of refference,so the values that read by ADS8860 should be 8000 as hexadecimal,but it was not,as we can see the picture I send last time ,and it changed from 7FFF to 7F00.