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CC2538: lowest power for performing ADC

John Wilson78927
Prodigy 20 points

Other Parts Discussed in Thread: CC2538

What is the lowest power requirement for using CC2538 doing ADC?  We don't need RX/TX active at the time.  Looking at the electrical characteristics table in the user manual, I see that there is a draw of 13mA with the 32MHz XOSC running; I also see that performing ADC takes 1.2mA.  Thus, is it simply (13 + 1.2)mA required to do ADC with no radio powered?

Thank you very much for your help,

John

  • 0
    TI__Genius 9180 points

    This depends on how well you want to optimize for power, if you use the ADC when 32-MHz XOSC is running with CPU running at 32-MHz and accessing flash, then this is correct.

    However you could optimize better by putting CPU in to idle while waiting for the ADC to converge.

    Regards, TC.

  • 0 in reply to TopCat
    TI__Genius 16570 points

    Hi,

    do you need to run your CPU core at 32 Mhz? Scaling down CPU frequency, if you can't set CPU to idel, can be another option.

    Thanks,

    TheDarkSide

  • 0 in reply to TheDarkSide
    Prodigy 20 points

    Thank you for the help with my question!  I've got a newbie question follow-up: in the CC2538 user's guide it says "RF, ADC, USB functionality requires that system runs from 32MHz XTAL".  Is it true that the 32MHz XTAL and the CPU speed are independent?  That is, the crystal can be running (which I assume the ADC requires) but separate from that the CPU frequency can be lowered or (as you and TopCat mention) even put to idle?

    Thank you,

    John

  • 0 in reply to John Wilson78927
    TI__Genius 16570 points

    Yes, of course. CPU clock is derived from the external clock (ie 32 Mhz crystal) but the CPU power state and clock state/frequency can be controlled independently, ie you can have your CPU in IDLE or running at a divided frequency of the external OSC, even if the external clock is running at 32 Mhz or even if it is not running, in case you use the internal RC OSC of the CC2538.

    Please check Chapter 7 of the CC2538 user's guide: http://www.ti.com/lit/ug/swru319c/swru319c.pdf

    Thanks,

    TheDarkSide