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MSP430FR2100: Low power operation below 100uA

Part Number: MSP430FR2100

I need a solution where the MCU draws less than 100uA with timers operating and digital outputs are kept in a high or low state. The simplest solution to this would seem to be to run the MCU in active mode at e.g. 32kHz. Is this possible, or will I need to run it at 1MHz and alternate between active mode and low power mode? If LPM is used, may outputs be kept high during LPM?

  • When I investigated this (on the F2 series, but I expect it still applies) I found that power doesn't scale down linearly with very low CPU (MCLK) speeds. I concluded it was better to run at a higher speed (0.5-1MHz) and use LPM liberally.

    GPIOs maintain their state in LPM. Timers generally run in LPM, though you should choose a timer clock appropriate to the LPM "depth". I encourage you to look over data sheet (SLASE78D) Table 6-1 to choose the LPM based on the features you want.

  • Thanks, this partly answers the query.
    My concern then is that when the CPU run in active mode this way, the supply current drawn by the CPU will be higher than what the power suplly supplies. This means that the main supply capacitor voltage (=voltage supplied to the CPU) will perhaps go down by let's say 0.2V during the active period. Assuming we are within the voltage band recommended for the CPU, is there any risk that this reduction of voltage may affect the operation of the CPU?

  • The MSP430 is quite agile when it comes to varying operating voltage (or clock speed). The DCO speed varies slightly with voltage, but the FLL can adapt for this. [Other data sheets specify the DCO variation with temperature and voltage, but I don't see that in this data sheet. The REFO is about 1%/V, which probably suggests an order of magnitude.] There are a few specific exceptions -- e.g. the ADC and eCOMP have a minimum of 2.0V.

  • Hi,

    Unlike Flash device, for FRAM device, you can run it at full speed in their operation voltage. So, the reduction of voltage will not affect the operation of the CPU.

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