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Original question:

ADS8860: SPI Interface between msp430 and ADS8860

ADS8860: Data converters forum

Dhiren Shetty
Prodigy 120 points
Part Number: ADS8860
Other Parts Discussed in Thread: REF6050, REF6030,

Hello Keith,

Thanks for your response. Found that the analog input pin was not properly connected to the source and therefore SPI communication was improper

Now I want to finalise the circuit

1) First when I had recieved the board ADS8860EVM I connected the board using PHY to my PC
and via software of TI found that there was a fluctuation of 150 counts which was reduced to 20 counts
after I changed the input capacitor C1 to 0.1UF
2) I wanted to then connect the board to my MCU board containing msp430
Therefore I have connected the SPI lines on the ADS8860EVM to my microcontroller msp430 and disconnected PHY.
Also bypassed REF6050 and gave 3.3V reference to the ADC.
Also the same 3.3V was also suppiled to AVDD and DVDD.
Now I have got ADC count with a fluctuation of upto 60 counts.
3) Now I believe that the fluctuation would reduce if I replace REF6050 with REF6030 instead of bypassing the reference.
I would like to know what more need to be done to improve the stability of the ADC output.
I have attached the schematic of ADS8860 where I have mentioned the changes in the schematic done on ADS8860EVM schematic
as comments

Please suggest whether the changes are sufficient to improve stability and get reduced fluctuations upto 20 counts
or whether any further changes are required. I am asking before hand so that I can incorporate any other changes
before I could finalise the circuit

With Regards,

Dhireninput power and refernce change.pdf

  • 0
    TI__Mastermind 36240 points

    Hello Dhiren,

    You are correct.  The reference input of the ADS8860 is a switched capacitor, and requires a high speed buffer to properly drive the input.  Simply connecting the REF input to a 3.3V power supply will work, but you will see a large increase in noise.  Replacing the REF6050 with a REF6030 will be your best option for low noise.

    You can also power the REF6030, AVDD and DVDD from a single 3.3V supply.  The TPS7A4700 LDO on the ADS8860EVM is a very low noise regulator (will require a 3.6V or higher input voltage).  You may want to keep a single TPS7A4700 near the ADS8860 to provide a very clean power source with the option to bypass if you find your main 3.3V supply provides good low noise results.

    Regards,
    Keith Nicholas
    Precision ADC Applications