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ADS114S08: ADS114S08 wake up time

Part Number: ADS114S08


Hello,

What is the wakeup time from Power Down Mode to Standby mode where the ADC is ready to start a conversion ?

Kind regards.

  • Hi Frederic,

    This is a little complicated to answer as it would depend on whether you are using the internal oscillator or an external oscillator. Let's assume the internal oscillator is being used. When the POWERDOWN command is issued, the internal oscillator, PGA, VBIAS, and IDACs are all turned off. Depending on the settings in VREFCON the internal reference may be turned off as well. After the 7th falling edge of SCLK for the WAKEUP command plus 2 *tMOD periods, the internal oscillator will start. The startup time for the internal oscillator is 4096 tCLK periods (aproximately 1ms). Once the internal oscillator has restarted, a few clock periods later the remaining circuitry will restart. So the wake up time is dominated by the startup of the internal oscillator.

    Let's say you issue the WAKEUP command immediately followed by START. The conversion result will be ready in 1ms plus the conversion time shown in either Table 13 or Table 15 (depending on the digital filter and data rate being used) plus any Programmable Conversion Delay programmed into the device (default setting is 14*tMOD periods where tMOD = 16*tCLK) to allow for analog settling prior to the start of conversion. The default time is approximately 55us.

    Depending on the measurement, and which internal devices are being used within the ADS114S08 there could be analog settling time required. For example, if the internal reference is used but is powered down, there will be a settling delay for the reference to settle to 2.5V. This will depend on cap loading on the REFOUT pin. The minimum cap size is 1uF, so it will take 5.9ms for the reference to settle (or longer if the cap is larger). The settling time is one reason why there is the VREFCON bit setting to leave the reference powered even if in POWERDOWN mode.

    If the IDACs are used to excite a sensor, then there could be additional analog settling time required for the input path to settle. So there are many additional things to consider apart from just the wakeup time which is about 1ms.

    Best regards,
    Bob B
  • Hello,

    Thank you very much for the very comprehensive answer.
    To precise my configuration I use PGA = 8, I have four differential channel to measure one time sequentially , I will use the internal ref with 1µF cap, 400 sps, low latency filter only, no IDACS.

    Kind regards.

    Frederic