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ADS8689: conversion data output

Gene Qiu
Intellectual 1720 points
Part Number: ADS8689
Other Parts Discussed in Thread: ADS8688

Hi team,

When using ADS8689, facing below 3 questions:

1. According to datasheet 7.4.2.3, at the end of conversion, the device enters ACQ state.  Does this means that before the next rising edge of the CONVST/CS signal, ADS8689 would stay at ACQ status?  Then what would the CONV result output after the rising edge of the CONVST/CS signal,  is it the samples data in latest 5us in ACQ state?

2.If the former frame send the order to set the input channel range, would the SDO outputs the results which just end conversion at next frame?  Customer tried ADS8688, it it the data which just end conversion. 

3.According to datasheet Table7-5, WRITE command only 16bit data is written, then what about how to write the 32bit register? Since for the ALARM_H_TH_REG is 32bit register

Best Regards

Gene

  • +1
    TI__Mastermind 46785 points

    Hi Gene,

    Here are answers:

    1. Yes, ADS8689 will stay at ACQ status until next rising edge of CONVST. Yes, the latest conversion data are shown in the ACQ state which is also the data read time in the timing diagram.
    2. The command will be executed at the rising edge of CONVST in the current frame. The SDO also output data in the current frame if SCLK clocks are sent to the ADC. However, the data are not accurate because the change on the input range will need time to settle.
    3. For programming a 32-bit register, the command (0x11010_00_) can be sent twice with two register addresses (e.g. 0x28 and 0x2A address for ALARM_H_TH_REG register).

    Best regards,

    Dale

  • +1 in reply to Dale Li
    TI__Intellectual 1720 points

    Hi Dale

    Thank you for your expert comment. One more question, After setting the channel input range, if the input range changes significantly, how much delay does it take before the rising edge of CONVT sent to achieve accurate acquisition results? If the channel input range  is unchanged,  need to wait?

    Best Regards

    Gene

  • +1 in reply to Dale Li
    TI__Intellectual 1720 points

    Hi Dale

    Thank you for your expert comment. One more question, After setting the channel input range, if the input range changes significantly, how much delay does it take before the rising edge of CONVT sent to achieve accurate acquisition results? If the channel input range  is unchanged,  need to wait?

    Best Regards

    Gene

  • 0 in reply to Gene Qiu
    TI__Mastermind 46785 points

    Hi Gene,

    The settling time depends on the internal LPF filter and resolution. For ADS8689, it requires approximate140us time to settle for 1/2LSB accuracy with 18-bit resolution. If there is no input range change, this is not needed.

    Best regards,

    Dale