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[FAQ] ADS129x: Why does the Device ID register show the incorrect number of channels?

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The ADS1292, ADS1298, and ADS1299 devices in the ADS129x bio-potential ADC family offer multiple channel variants. Sometimes, the value read from the Device ID register may reflect the incorrect number of channels. Why does this happen?


Ryan Andrews

Applications Engineer | Precision ADCs 

Are you working on a bio-potential application? Check out these helpful resources: ADS129x FAQ | ECG Online Training

  • Most of the time, an incorrect Device ID is caused by an improper power-up sequence. After your system powers on, both the ADC's analog and digital supplies require some time to ramp to their final value. In addition, there are internal voltage nodes generated from the supplies that must ramp as well, such as the internal bandgap voltage (VBG). The internal bandgap is used to bias much of the device's internal circuitry and can be connected to an external bypass capacitor for filtering on the VCAP1 pin. It's important for VBG to fully ramp since it is needed to read the one-time programmable (OTP) bits that contain the channel count information and are set during the device's final test program. Depending on how fast the supplies ramp, these bits may be misread and default to another value.

    An external /RESET pulse is strongly recommended after power-up to ensure the device initializes in a known good state. Check the Power-Up Sequencing section in the datasheet to determine when to toggle the /RESET pin and begin using the device. As an example, refer to the figure below from the ADS1298 datasheet:

    FIGURE 1: ADS1298 Power-on Reset Timing

     

    Link to BIOFAQ homepage

    This post applies to ADS1191ADS1192ADS1291ADS1292ADS1292RADS1294ADS1294RADS1296ADS1296RADS1298ADS1298RADS1299-4ADS1299-6, and ADS1299.


    Ryan Andrews

    Applications Engineer | Precision ADCs 

    Are you working on a bio-potential application? Check out these helpful resources: ADS129x FAQ | ECG Online Training

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