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CC1110 Power supply monitor

ronnym
Expert 1835 points

I am using the CC1110 in a Lithium Ion powered app. I have a 2.5 volt LDO regulator, and would like to monitor the Lithium cell as simply and inexpensively as possible. At a preset voltage, the chip would go into PM3 until recharged and reset. Using a resistive divider between the battery and ground, and monitoring the voltage with the internal A/D would work, but create constant drain on the battery. The internal brown out detect would restart the chip and cause it to oscillate on and off. Any other ideas? I'de prefer to not add another voltage monitor chip...

Thanks, Ron

  • 0
    Mastermind 8170 points

    Someone probably has a better idea but here are a few thoughts:

    1.) Use the divider, the ADC input R is 197K @ 4 MHz, likely higher at a low sample rate.  You should be able to get by with  <30ua total.
    2.) Use a small MOSFET and a GPIO to energize the divider and disconnect it when not needed. You might consider charging  a small sampling cap to reduce the time the MOSFET needs to conduct.
    Both of these use the ADC permitting low battery warning, change of sample period (and Tx) when the battery is getting low etc. Note the ADC current is 1.2ma when measuring.

    My favorite:

    3. Use a window comparator (JFET type op amp will work). It will set there at pico to nano amps. Use it to generate an interrupt when its output flips due to the low voltage point being reached on its input. If you do not want to use a interrupt simply poll the comparator's output periodically. Figure $.50 in parts.