How do I calculate/predict power consumption of a microcontroller?

Discussion in 'Embedded Systems and Microcontrollers' started by shankaryr, Jul 21, 2008.

  1. shankaryr

    Thread Starter New Member

    Jul 21, 2008
    7
    0
    Hi there,

    I am working with a TI MSP430 series microcontroller. My circuit has a couple of resistors, a capacitor and the TI microcontroller. I would be switching the microcontroller to into active mode every ten minutes and perform a data acquisition. It would run the code and calculate the required value. The value is stored in the flash memory which is present on the uC. How would i calculate/predict the power consumption of my uC system. There is no LED/LCD display. I would read info. from the uC every two months.

    So, I would like to know the battery capacity required to run it for a couple of months. I would also like to know the general method of finding the way to calculate the power consumed by any uC system.

    Thanks. All help is appreciated.

    Shankar
     
  2. shankaryr

    Thread Starter New Member

    Jul 21, 2008
    7
    0
    Hi,

    Also, could some suggest some batteries to embed in the system which outputs 3.3v. Something which could be soldered on the chip? Ideas on rigging the circuit will be a bonus.

    Thanks.
    Shankar
     
  3. roddefig

    Active Member

    Apr 29, 2008
    149
    0
    I think the most straight-forward method would be to use a multi-meter that can log the current over time. That will give you an idea of the power over time.
     
  4. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    The datasheet has numbers for the current consumption for active mode and for low power modes using different clock speeds. You can start there. How long will the unit be in active mode?

    Just a quick example:

    If you assume that it will be in active mode for maybe <100ms and the sleep mode is 10 minutes then you can as a first order ignore the active mode current draw (unless it is HUGE). The great majority of power will be consumed during sleep -- this will be in the uW range-- uA * Vdd. A CR2354 coin cell has ~ 560mAh. Derate this to 420mAh.

    420mAh/20uA = 21000 hours (assuming sleep current is 20uA micro + other stuff)

    This also assumes a relatively stable temperature and that the "other stuff" is either off or not connect while the micro is sleeping. Also be aware that batteries do not have a flat discharge curve (lithium cells are pretty flat though) and as such you need to consider your measurement circuit when the battery is nearing end-of-life.
     
  5. shankaryr

    Thread Starter New Member

    Jul 21, 2008
    7
    0
    Hi there,


    Thanks a lot. That was very useful. By the way, when we say 20uA or 50 uA or 50mA, what are we refering to? How do we know the current over time which should give us a stat about the consumption. I am just curious but the calc. you did was indeed very helpful.

    Thanks
     
  6. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    It is the current "leaving" or "returning" from the battery. So as roddefig suggested you can hook up a multimeter in series and measure the actual current to make sure you have everything programmed and hooked up correctly.
     
  7. shankaryr

    Thread Starter New Member

    Jul 21, 2008
    7
    0
    thanks for the info.
     
Loading...