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I have a question regarding optimising design for ultra low power consumption device. I'm trying to develop a remote sensor node that should measure and send data every few hours.

Currently I have an RTC (DS1337) that wakes up my MCU (ATMEGA328P) from deep sleep via hardware interrupt. While the sleep current is fairly low ( avg 76 uA), it is still a fairly large amount if I aim for a device to run in the wild for couple of years.

Could I instead, use the RTC to ENABLE/DISABLE the 3.3v LDO (MIC5404) thus shutting completely down the MCU and have the RTC runs on a separate coin cell battery? I think this is called power-gating. What will be the hidden disadvantage ?

Thanks!

RTC: https://datasheets.maximintegrated.com/en/ds/DS1337-DS1337C.pdf

LDO: http://ww1.microchip.com/downloads/en/DeviceDoc/MIC550x-300mA-Single-Output-LDO-in-Small-Packages-DS20006006A.pdf

Waz
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    We need links to the datasheets for the RTC and LDO. – Elliot Alderson Feb 27 '19 at 17:05
  • Hi Elliot, I have edited the original message, adding the reference for MCU,LDO and RTC. Thank you – Waz Feb 27 '19 at 17:11
  • Your ATmega probably doesn't need a regulator at all. What sort of battery are you using? – Chris Stratton Feb 27 '19 at 17:14
  • 3.6V Li-SOCL2 (LS14250) currently, but I'm looking to use coin cell 3V battery instead for form factor reduction. If there is no need for an LDO indeed, then I would do power gating via JFET instead. However my question remain, as I fail to see any disadvantages of power gating vs. wake/sleep. – Waz Feb 27 '19 at 17:15
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    Please provide **links to the datasheets** for the RTC and LDO. Don't make us search for them. – Elliot Alderson Feb 27 '19 at 17:15
  • What is the lowest power consumption of the MCU in a mode from which it can only be woken by external signal? What else is in the circuit which might not be able to take the full battery voltage which the ATmega needs to communicate with, and by what means of communication? – Chris Stratton Feb 27 '19 at 17:30
  • Hi Chris, the lowest power I have obtained is 76uA with 3.3v and external crystal 8Mhz, and some fuse setting optimisation. The communication mode is a LoRa module that is also power-gated by the MCU (or sleep mode, i have yet to look this up). There is also an ultrasonic transducer system that is powered from a 5V boost convertor, but the 5V boost convertor is disable while MCU is in sleep mode or shutdown, so it does not account for my "long term" power consumption. So in short, every other aspect of that design does not require power before the MCU get to wake up and enable them. – Waz Feb 27 '19 at 17:35
  • You're not really considering the issues of supply voltage differences between parts of the circuit (or for that matter, signals between chips powered at different times). And it doesn't sound like your MCU is in its lowest power mode - quick looking suggests you should be able to get to the 5-6 uA range, possibly even to less than a uA. – Chris Stratton Feb 27 '19 at 18:32
  • 76 uA seems really high for this part - how are your fuses configured? I can usually get down near 1 uA. – John Birckhead Feb 27 '19 at 19:01
  • ATmega low power modes https://electronics.stackexchange.com/a/49233/2246 – Chris Stratton Feb 27 '19 at 19:09

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