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ADS1255: Ask about ads1255 sampling error

Part Number: ADS1255
Other Parts Discussed in Thread: REF5025, LM324, LM358, OPA192

In the process of using the ads1255 chip to collect the voltage, the registers I set are as follows:
Single-ended acquisition, buffer is turned on, gain=1, self-calibration is turned on, sampling rate is 1000sps, (also tried 2000sps) reference voltage is 2.5v
The voltage is collected by a single conversion method, and the collected voltage occasionally has an error of 1mv, such as 1.406v, then 1.405. Under the accuracy of 24bit, is the fluctuation of 1mv normal?
Is it necessary to lower the sps?

  • Hi Ming,

    It should not be necessary to lower the sample rate on the ADS1255. Since this error is occasional, it should not be dependent on the data rate.

    What is the reference voltage source you are using? Is it a precision reference e.g. REF5025? Is it buffered?

    Also, please note that with the buffer = on, the minimum input signal on AINN is 0V. If there is any fluctuation in your ground reference, this could violate the absolute input voltage requirements on the ADS1255.

    If you can share a schematic that would be helpful.


  • I currently use the ads1255 chip for voltage sampling

    The register configuration is as follows:

    STATUS = 0x36
    MUX = 0x08
    ADCON = 0x20
    DRATE = 0xa1
    IO = 0xe1

    On the circuit, aincom is grounded, and what I sampled is a single-ended sampling method, SYNC-》WAKEUP, wait for DRDY low level, and then send RDATA-》STANDBY

    First, I would like to ask whether such a design scheme and register configuration are reasonable

    Second, does the setting of sps affect the sampling accuracy?

    The following is the data I collected, 20 consecutive collections, the last one is the average value, the input voltage is above 1v, relatively speaking, the deviation is plus or minus 1mv

    When I reduce the input voltage, the error of the continuous acquisition is relatively large, the unit is mv

  • I use the single conversion mode for each acquisition, and each acquisition is separated by 10us. Will this affect the sampling accuracy of ads1255? Will the chip be damaged?
    ps: After I configure the register, the register value read is also correct.
    Among them, after resetting, I tried to read the value of the IO register and found that it was inconsistent with the value in the data sheet. Could the chip be broken?

  • Ads1256调试.docx

    This word document is the register value record when I debug

  • Hi Ming,

    Please note that the amplifiers you are using (LM324 and LM358) both have 1-2mV of offset (typical). Are you calibrating this out?

    The ADS1255's SELFCAL option only calibrates the offset and gain error of the ADC, not the external system. If you want to calibrate the system, you would need to apply a 0V input (usually shorting the inputs to a mid-supply voltage) for the offset calibration and a full-scale input (~95% of full-scale) for the gain calibration.

    Please try this and let me know what happens. Or select lower offset amplifiers such as OPA192