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ADS1278: Low-Power and Low-Speed consumption difference at low frequency

Benjamin Nordman
Intellectual 410 points
Part Number: ADS1278


Hello TI Community,

I need to send data from two ADS1278 in Daisy Chain (16 channels) to a MCU with a data rate Fdata_min = 2kHz

To this purpose I use a 2.048MHz oscillator.

As I want the ADC to consume as less power as possible, I set it at first in "Low Power" mode (MODE[1:0] = "10") with CLKDIV = 1, so I have Fclk/Fdata = 512 and a Fmod/Fdata=64.

Then I get a Fdata = 4kHz and Fmod = 256kHz.

However, I noticed ther Low-Speed mode was less power consuming than the Low-Power one (50 to 80mW  instead of 245 to 355mW according to the page 5 of the datasheet, which is a big difference!).

Then, I hesitate to set at Low-Speed instead of Low-Power mode (with CLKDIV = 0 to get the exact same frequency ratio with the same oscillator), because I wonder why, with the same clock/data/modulation frequencies, there could be such a big consumption difference between these two modes.

Could you please give me some explanation?

  • +1
    TI__Mastermind 47090 points

    Hello Benjamin,

    As the maximum allowed data rate is reduced, there is more time for the internal amplifiers to settle during the acquisition period.  With more time to settle, the internal bias currents of the amplifiers are further reduced which reduces total power consumption.  Since low-speed mode has the lowest maximum allowable data rate of 10,547sps, this results in the lowest power consumption.  

    Low-power mode reduces the maximum data rate from 144,531sps to 52,734 which allows some reduction of the internal bias currents, but not nearly as much as in low-speed mode where the maximum data rate is limited to 10,547sps.

    For your application, I suggest you use Low-Speed mode; this will result in the lowest power dissipation and better SNR than Low-Power mode.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Intellectual 410 points

    Hello Keith,

    That perfectly answers my question and this is a good information to know :-)

    Thanks for this quick reply!

    Best Regards,

    Benjamin