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LPM0 vs LPM1

Warren Langley
Prodigy 190 points
Other Parts Discussed in Thread: MSP430FR5969

I have a MSP430FR5969 application in which I am using DMA and the UART in a low power mode.  Because the UART uses SMCLK which is sourced by the DCO, the best possible mode is LPM1 (I believe).  I thought it was interesting that the observed power consumption in LPM1 was ~350uA and in LPM0 was ~200uA.

The descriptions above look identical.  Any thoughts on why LPM1 would have higher power consumption than LPM0?  Where can I find more information on the differences between LPM0 and LPM1.  Thanks!

  • 0
    Guru 227245 points

    The LPM0 description seems to be wrong. AFAIK, DCO remains enabled in LPM0, even if not used by ACLK or SMCLK. In LPM1, the DCO gets disabled if not currently used by an active clock. (so LPM1 reverts to LPM0 if the DCO is required for SMLCK or ACLK). LPM2 then also disables the DCO bias generator.
    It takes some time to return from LPM1 to active mode, and even longer to return from LPM2.

    Power consumption (actually the average power consumption) is higher in LPM1 if the device switches from LPM1 to active mode often. In this case, there is some dead time between an interrupt and re-activation of the CPU, because the DCO needs to be started and has to settle first. Under certain circumstances, this may lead to a higher average power, even though during the time where the device is in LPM1, the power consumption is lower than during LPM0.
    For the time the device is completely dormant in LPM1, the power consumption should be below LPM0.

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