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ADS8350 with 2.5V = Vref = AINM pins.

m Teckin
Prodigy 10 points
Other Parts Discussed in Thread: ADS8350

Currently I 'm using ADS8350 in my design. Am following the application similar to page 30 of the ADS8350 datasheet. I encountered the digital dat jumping on the SDO-B output (from 0x00FF to 0xFF00 and sudden jump up to 0x2000 then back to normal) when the ADC input is at zero level (Input = 2.5V same as Vref).

Simultaneously reading SDO-A and SDO-B data, the SDO-A data is stable and I'm able to get correct reading between 0x00FF (+ve) to 0xFF00 (-ve).

May I know is there any other setting that I have missed that result the digital data jumps on SDO-B output?

  • 0
    TI__Guru 54576 points

    Hi M Teckin,

    Welcome to the forum. 

    With AINP and AINN set to 2.5V, the ADS8350 expected conversion result should be close to x0000h or x7FFFh (two's complement format). 

    The ADS8350 is a SAR converter, therefore it needs to be driven with a low impedance source.  Depending on the sampling rate, the device will require an appropiate driver amplifier and RC filter that is able to charge the internal sample and hold to the expected input voltage.  The RC filter also helps attenuate the sampling charge injection from the switched-capacitor input stage of the SAR ADC.  In addition to an input driver circuit, an appropiate reference driver circuit is required.    Page 26- 33 suggest a couple of circuits.

    If possible please post oscilloscope plots while reading conversion data (CS/SCLK/SDOA/SDOB) while the AINM/AINP inputs are driven to 2.5V. Please post an schematic detailing the driver circuit, RC filter, supply connections and bypass capacitor used.  What sampling rate is required in the application? 

     Thanks and Best Regards,

    Luis