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ADS131E04 external clock

Ireneusz Magiera
Intellectual 335 points
Other Parts Discussed in Thread: ADS131E04

What kind of clock source can be used as external clock for ADS131E04? 2.048MHz is rather not typical frequency and generators are harder to find than i.e 2MHz. What more, datasheet states that external clock should be turned off in power down mode to reduce power consumption.

I was thinking of driving CLK pin from MCU (with external 20-30ppm crystal as clock source) output tied to timer/counter. Is that a good option? Or should be avoided?

2.048MHz is a nominal frequency. Am I correct that all data rates will be scaled proportionally to change of external clock? I.e for 2MHz instead of 1, 2, 4, 8, 16, 32, and 64 kSPS data rates there will be 0.98, 1.95, 3.9, 7.81, 15.6, 31.25 and 62.5 kSPS.

  • 0
    TI__Mastermind 23235 points

    Mr Magiera -

    2.048MHz is a fairly standard number as it works well since it is a power of 2.  A quick search on a site like Digikey, Mouser, or similar reveals a good selection, so you might try looking at one of these sites.

    Regarding the master clock value, the device is a delta-sigma converter (also know as oversampling) converter.  The input signal is oversampled at a rate of  which is then decimated to the output data rate.  The relationship of fmod/fdr is called the oversampling ratio, or OSR. (fmod = fclk/2 for this device)

    The specs for the external clock tolerance is shown in the spec table at the beginning on the datasheet (pg4) and the OSR values can be calculated from Table 11.

  • 0 in reply to Greg Hupp
    Intellectual 335 points

    Thank you for your answer. I have checked (big) local distributors again and 2 of 3 doesn't have 2.048MHz oscillators in their offer and the last one has one but.. not in stock at the moment :) So maybe it's uncommon here, locally, and I was misleaded.
    Farnell has some but none of them is low power (32mA in battery-powered equipment is a little bit too much).

    So maybe it's time for import.

    One more question about sampling - when I wish to apply anti-aliasing filter I should take fmod or fdr into account? I guess fmod but I'd like to be sure.

  • 0 in reply to Ireneusz Magiera
    Expert 2585 points

    Ireneusz Magiera said:
    One more question about sampling - when I wish to apply anti-aliasing filter I should take fmod or fdr into account? I guess fmod but I'd like to be sure.

    When we talk about anti-aliasing filter  we talk about real signal and fmod. Anti-alias filter should  attenuate interference with  fmod  anz signal above fmod which could impact the accuracy.