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Original question:

ADS1271EVM: ADS1271EVM - DRDY problem

ADS1271EVM: [Problem] ADS1271EVM - AC analog input and DOUT issue

Evan Fang
Prodigy 30 points

Part Number: ADS1271EVM

Hi sir,

I am using ADS1271evm and stm32f7 to communicate via SPI,

THe CLK is 27MHz , SPI Baud rate 13.5MBits/s , SYNC connect with High , Vref = 2.5V

When i give DC(-2.5~2.5) as analog input ,  Dout is correct through  conversion of data

The SPI format and DOUT is below:

SPI FORMAT

DOUT


But when i give AC Sine wave as analog input, the Dout have some problem

When AC sine wave amplitude below 0.5 V (10Hz) , the Dout is correct , image below

But when AC sine wave amplitude higher than 0.5V , Dout is distortion , how can i resolve it ? thanks.

The issue image below 

SPI FORMAT


DOUT 

  • 0
    TI__Mastermind 36010 points

    Hello Evan,

    Are you using the on board amplifier?  If so, did you connect an external power supply per below?

    If you intend to utilize the analog signal buffers on the EVM, connect ±15V and ground via J14 terminal connections +VA, -VA, and GND on the MMB0.


    Are switches S1 and S4 in the proper positions to select the input amplifier?  (I am assuming you are using channel 1)


    The ADS1271 inputs are differential.  You can use single-ended inputs, but you must connect one of the inputs to system ground.  Can you share a connection diagram on how you have the board configured?

    Please provide the following measurements to help debug the board issue.

    1. With +2.5V on the amplifier input, please measure the voltages (with respect to ground pin 3) on each of the ADC input pins, AINP (pin 1) and AINN (pin 2).  You should measure 3.75V on AINP and 1.25V on AINN.

    2. With -2.5V on the amplifier input, please measure the voltages (with respect to ground pin 3) on each of the ADC input pins, AINP (pin 1) and AINN (pin 2).  You should measure 1.25V on AINP and 3.75V on AINN.

    Also, with +2V and -2V inputs, what are the output codes of the ADC?

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Prodigy 30 points

    Hi Keith Nicholas

    Thanks for your response, it's resolve .

    I don't supply external power for signal generator, and device common ground .

  • 0 in reply to Evan Fang
    TI__Mastermind 36010 points

    Hi Evan,

    I am glad you were able to fix the problem.

    Regards,
    Keith