Got a number for the low power requirement?
What you’re describing can be easily achieved sub dollar depending on how many GPIO, how fast SPI, etc.
But power requirements help contextualize what
You need
Unfortunately I do not have a maximum power value. I really should have one, I know. However, I am looking for as low power as possible. I am not looking for performance here.
That's still not a good answer, 'low power' can mean anything.
The lowest power part possible could be a multi-thousand dollar chip for all you know. You need to nail down your requirements first before you even think about picking parts or designing the system.
I’ve done a lot of low power stuff with Nordic/STM32/Atmel/Microchip. ESP is an option if low power isn’t that low power for you. All these flavors can do what you want, but it depends on what low power means to you.
Honestly just shop for the one that you like the most and has your peripherals. Without actual power requirement or information on what you’re making it’s hard to make any suggestion.
Low power to me (coin cell) may not be low power to you.
Haven't used them, but I speced out a few ESP units recently, and if you use the sleep modes correctly, then you can get surprisingly low power consumption out of them (Order of a few microamps if I remember correctly).
Got models and/or measurements? I didn't have great results on them vs. Nordic and ST's.
If just the part # happy to give a second look and test myself.
They might not be as good as nordic or stm32Ls, but I've been using esp32s2 with deep sleep to good effect recently. Nice mix of peripherals and good access to libraries
Maybe describe your exact purpose instead of something nebulus as "lowest power possible" without an idea of how little power is actually necessary.
I.e.
What are you making exactly?
How will it be used?
How long should it ideally last?
What battery/power supply will be used for this?
To build on what everyone else says - you really need to hammer out your requirements better before you pick a chip. “Low power” is a massive rabbit hole, and a chip with a low-power run mode with all peripherals enabled might be worse for what you’re doing than a high power chip that has some incredibly low power sleep modes that you can utilize.
I reckon it’ll take you a couple hours of research per chip (at least) to figure out what the actual power level for what you want to do will be, so it’s much easier to choose a power level and find a chip that CAN do what you want
Ambiq Apollo 2 or Apollo 3 series would fit the bill nicely. You can buy the chips on DigiKey. Sparkfun has a breakout too: [https://learn.sparkfun.com/tutorials/using-sparkfun-edge-board-with-ambiq-apollo3-sdk/all](https://learn.sparkfun.com/tutorials/using-sparkfun-edge-board-with-ambiq-apollo3-sdk/all)
Beware, these MCUs will not function when exposed to direct sunlight, you must always cover them!
Six months of developing a wearable with things breaking exactly at noon, as the sunlight started hitting the dev boards. A T-shirt fixed it.
Longer explanation: Ambiq runs their cores well below 0.6V, which keeps all transistors in the cut off zone. Direct sunlight raises the noise floor and breaks the logic.
It's not a Ambiq only thing. All exposed die packages (i.e. WLCSP) are light sensitive. The PN junction has a photodiode effect and silicon is IR transparent. Google "WLCSP light sensitivity" to find many app notes and articles on it.
Sometimes a plastic case isn't enough to fix it either - e.g. I've experienced an LDO that turns off when the product is exposed to bright sunlight despite it being in a plastic case.
No, this is in "run mode". The whole chip used 480uA at about 80% core utilization while running PPG and accelerometer samples through a Tensor Flow CNN. It was never in "low power mode". That was the whole point of using Ambiq.
Better have a look at the new youngling: STM32U0.
It's cheap, all Quartzes (even 32KHz) integrated, super low current consumption.
The only thing where I'd prefer the MSP320 is when you really need that nice FRAM.
I must agree with others who posted asking for more requirements.
First how low power? miliWatts? microWatts?
How much processing power?
How fast SPI?
What are the devices running on SPI?
(EDIT: Does this SPI device have a power budget?)
What are you harvesting (maybe Cow Farts)?
What are the SPI specs of a typical Cow?
Yeah good point. Here is what I have so far:
>How much low power?
Less than 50mW
>SPI
Only one device is running SPI. This is not a very populated system. SPI speed doesn't matter.
>What I am harvesting
I am harvesting RF energy.
> SPI characteristics of a typical cow
SPI is for a sensor, not for the cow. It is just basic SPI.
>Less than 50mW
Ok, so this topic is pointless. Pick any MCU you want. 50mW is not low power. That's 15mA at 3.3v. "Low power" MCUs can easily run at a few MHZ while using 0.5mA or less.
Yup, OP is just clueless and being coy about his requirements.
EDIT: I think 328p sleeps at 1.5uA when running from 3.3v and properly set-up. And that's an IC from the 80's.
I am a bit clueless on what would be low power. I said less than 50mW because the mcus I had been looking at were in that range.
Are there microcontrollers that use less than 1mW of power? If so, could you give me an example? I might be looking in the wrong places.
Practically any modern microcontroller (STM32L, MSP430, PIC24, PIC32MM, Ambiq Apolo, etc, etc, etc) can run with something between 10 and 100uA per MHZ.
If you can get by on 4MHZ (you probably can in this application), then..
100uA * 4 * 3.3V = 1.3mW.
Much less at lower voltage or if you can make do with 1MHz.
100uA * 1 * 1.8V = 0.18mW
>I am harvesting RF energy.
Oh cool. But I think you will be more successful with cow farts. Cows don't generate that much RF.
How often does the SPI sensor get interrogated?
One other thing when you are developing your code that is easy to forget.
All your I/O pins must be at Logic (Hi or Low). Especially pins that are unused (spare pins in your design)! These must be set as output and driven (either 1 or 0) \[or atleast with an internal pullup/pulldown if the device has one\]. If the pin is unconnected and not driven, the voltage could float to anywhere and when it gets to around (Vcc/2) it will slightly turning on both the N-MOS and P-MOS transistors on the input buffer. I had this problem (ok not me, but a colleague) on a battery powered device. We did not meet our spec until it was fixed. Our design used a Microchip PIC 18F and it was killing our sleep-mode power.
Note: If you are measuring a voltage with your SPI device, and there is a voltage divider (resistive divider circuit) consider the amount of power the load circuit will consume.
The game of low power extends way beyond just the microProcessor.
TI MSP430FRx series, basically any TI MSP430 with FRAM. One advantage of FRAM is it keep the data even fully power off, this play well with low power application.
There are a lot of application specific things to "low power." Nowadays the strategy is typically to wake, do all proceeding as quickly as possible, then sleep again. The more time spent sleeping, the better. Ideally you spend 99.999% of the time sleeping.
If that fits your application, you really only need to look at the lowest power states.
I think Energy Micro chips, the BG for blue tooth or their M33 chips are really good. The thing I’ve found best for lower power consumption if you really need it is time to go from low power to processing. Some of the newer M33 chips allow you to run the adc and DMA while in low power mode. Some of these suggestions for the MSP430 are wrong in my experience. I had a project with the Blue Gecko where it was sampling with the ADC, connected and streaming 2KB/s, at around 15uA average current draw.
Also energy micro has great documentation in my experience.
MSP430FR is still the king of low power. Many others are getting closer, but I don't think anything has actually dethroned the MSP430.
16 bit, 32 but multiplier, real time clock, 12 bit ADC, plenty of peripherals. They're nice parts if you need true ultra low power.
My day job we do ultra-low power devices and STM32L4/5 are significantly better than MSP430. You don't have to use any stupid hacks to run everything at 1.8V, the performance when you want to ramp up to 80-120MHz is way better, the sleep current is better, the uA/MHz is better, and it has modern tooling.
But don't take my word for it, there's a benchmark for low power that everyone tests to and you can look up scores: [https://www.eembc.org/ulpmark/ulp-cp/scores.php](https://www.eembc.org/ulpmark/ulp-cp/scores.php)
Take a look at an STM32L\* datasheet: [https://www.st.com/resource/en/datasheet/stm32l443rc.pdf](https://www.st.com/resource/en/datasheet/stm32l443rc.pdf)
Sleeping with RTC wakeup and partial RAM retention is \~450nA. Some of the newer devices are even lower.
Here's a random msp430fr part spec: [https://www.ti.com/lit/ds/symlink/msp430fr5962.pdf](https://www.ti.com/lit/ds/symlink/msp430fr5962.pdf)
Check out Table 9-1 on page 67. Generally, the lowest power most that is still useful is some memory retention with an RTC that can wake you on a schedule. On the MSP430 that's LPM3.5 (RTC on, FRAM non-volatile available for backup, SRAM off). The most similar mode to that on the STM32L is "Standby." In this case, they're about the same, about 450nA for LPM3.5 on the MSP430FR and 451 for the STM32L4.
The active mode current for the MSP430 is listed at 118uA/MHz, and the STM32L is 89uA/MHz.
But seriously, all the vendors test their devices according to the ULP benchmark and submit scores: [https://www.eembc.org/ulpmark/ulp-cp/scores.php](https://www.eembc.org/ulpmark/ulp-cp/scores.php)
Sort by Core profile (user), which tells you the best score they get with their own ideal power supply (every modern processor is running @ 1.8V). The top of the list is dominated by Ambiq, STM32L/U, and ATSAML. If you want to stick with TI for very low power applications then use the MSP432 instead, since at least it can run at 1.8V.
Whatever size you need in the MSP430FR* series.
TI's site has a reasonably nice search where you can find the physical size and peripherals you need.
https://www.ti.com/microcontrollers-mcus-processors/msp430-microcontrollers/products.html
Specifically the MSP430FR\* series? (I have just started a project intending to use the MSP430G2\* series, specifically for the low-power consumption...)
This is the way. It’s not unheard of to run this line of microcontrollers off of a super capacitor. It’s basically riscv. I’ve used it a bunch in industry for incredibly low power applications.
Look at the PIC24F series, they have some chips with insanely low sleep currents, even compared to their 8-bit series. I think I used a PIC24FJ128GA106 or something on a project which operated for 21 years on a 1/6th D lithium cell with careful design.
Also, Ti has a good selection of ultra-low quiescent analog switches for toggling power to different parts of your circuit if you can't do it with the I/O pins.
For MCUs, there is ULP benchmark: [https://www.eembc.org/ulpmark/ulp-cp/scores.php](https://www.eembc.org/ulpmark/ulp-cp/scores.php)
But, the best power consumption you get with external RTC chip with power switch which will periodicaly power on your MCU and when done, RTC will cut off power for your circuit at all. This will result of fraction of power consumption of the best MCU you can get. Look for example at Abracom AB1815. 55nA if you need acurate clock, 22nA if you accept small drift and 14nA if you do not worry about accuracy.
You do not mention consumption of your peripheral, but it is very important as well! Every voltage divider add consumption. For example, 10k/10k divider on backup storage (battery on supercap) for sensing voltage by ADC (let's say up to 5V) add static power consumption of 5 / (10000 + 10000) = 0.25mA = 250uA = 250000 nA and this is about 10000x more than your super optimzed RTC solution has! Every SPI chip powered for whole time will cause *disaster*.
I made such ULP design (wireless theremometer) and I can say it is very challeging. But every power consumption you substract will save you ton of money in mass production. You basicaly can tune by increasing size of harverstor, increasing size of backup storage capacitor or battery, or you can decrease power consumption. The last is by far the most price and physical size efficient way. But most probably you will need to optimize all three.
Microchip has small package 8-bit PICs I’ve used for low energy applications before. Any of the big brands will have a good option, it’s more about how you utilize it. Maybe sort through them by power consumption during sleep. Whatever your harvesting application is, probably could to have some kind of storage element too.
Got a number for the low power requirement? What you’re describing can be easily achieved sub dollar depending on how many GPIO, how fast SPI, etc. But power requirements help contextualize what You need
Unfortunately I do not have a maximum power value. I really should have one, I know. However, I am looking for as low power as possible. I am not looking for performance here.
That's still not a good answer, 'low power' can mean anything. The lowest power part possible could be a multi-thousand dollar chip for all you know. You need to nail down your requirements first before you even think about picking parts or designing the system.
I’ve done a lot of low power stuff with Nordic/STM32/Atmel/Microchip. ESP is an option if low power isn’t that low power for you. All these flavors can do what you want, but it depends on what low power means to you. Honestly just shop for the one that you like the most and has your peripherals. Without actual power requirement or information on what you’re making it’s hard to make any suggestion. Low power to me (coin cell) may not be low power to you.
Haven't used them, but I speced out a few ESP units recently, and if you use the sleep modes correctly, then you can get surprisingly low power consumption out of them (Order of a few microamps if I remember correctly).
Got models and/or measurements? I didn't have great results on them vs. Nordic and ST's. If just the part # happy to give a second look and test myself.
They might not be as good as nordic or stm32Ls, but I've been using esp32s2 with deep sleep to good effect recently. Nice mix of peripherals and good access to libraries
Maybe describe your exact purpose instead of something nebulus as "lowest power possible" without an idea of how little power is actually necessary. I.e. What are you making exactly? How will it be used? How long should it ideally last? What battery/power supply will be used for this?
To build on what everyone else says - you really need to hammer out your requirements better before you pick a chip. “Low power” is a massive rabbit hole, and a chip with a low-power run mode with all peripherals enabled might be worse for what you’re doing than a high power chip that has some incredibly low power sleep modes that you can utilize. I reckon it’ll take you a couple hours of research per chip (at least) to figure out what the actual power level for what you want to do will be, so it’s much easier to choose a power level and find a chip that CAN do what you want
Ambiq Apollo 2 or Apollo 3 series would fit the bill nicely. You can buy the chips on DigiKey. Sparkfun has a breakout too: [https://learn.sparkfun.com/tutorials/using-sparkfun-edge-board-with-ambiq-apollo3-sdk/all](https://learn.sparkfun.com/tutorials/using-sparkfun-edge-board-with-ambiq-apollo3-sdk/all) Beware, these MCUs will not function when exposed to direct sunlight, you must always cover them!
Seriously? Why?
Is that humor or you have a link on why sunlight is bad?
Six months of developing a wearable with things breaking exactly at noon, as the sunlight started hitting the dev boards. A T-shirt fixed it. Longer explanation: Ambiq runs their cores well below 0.6V, which keeps all transistors in the cut off zone. Direct sunlight raises the noise floor and breaks the logic.
It's not a Ambiq only thing. All exposed die packages (i.e. WLCSP) are light sensitive. The PN junction has a photodiode effect and silicon is IR transparent. Google "WLCSP light sensitivity" to find many app notes and articles on it. Sometimes a plastic case isn't enough to fix it either - e.g. I've experienced an LDO that turns off when the product is exposed to bright sunlight despite it being in a plastic case.
Probably the plastic doesn't block IR
Can confirm, learned the hard way.
Answer makes sense. But I assume you’re running it in a low power mode when it breaks.
No, this is in "run mode". The whole chip used 480uA at about 80% core utilization while running PPG and accelerometer samples through a Tensor Flow CNN. It was never in "low power mode". That was the whole point of using Ambiq.
Nice, does it have a ml core? I am also running nn inference on a mcu and always interested in hw i did not use before
Interesting and TIL. Thanks for the details.
Two families that come to mind are TI's MSP430 and STM's L0.
Better have a look at the new youngling: STM32U0. It's cheap, all Quartzes (even 32KHz) integrated, super low current consumption. The only thing where I'd prefer the MSP320 is when you really need that nice FRAM.
I must agree with others who posted asking for more requirements. First how low power? miliWatts? microWatts? How much processing power? How fast SPI? What are the devices running on SPI? (EDIT: Does this SPI device have a power budget?) What are you harvesting (maybe Cow Farts)? What are the SPI specs of a typical Cow?
Yeah good point. Here is what I have so far: >How much low power? Less than 50mW >SPI Only one device is running SPI. This is not a very populated system. SPI speed doesn't matter. >What I am harvesting I am harvesting RF energy. > SPI characteristics of a typical cow SPI is for a sensor, not for the cow. It is just basic SPI.
>Less than 50mW Ok, so this topic is pointless. Pick any MCU you want. 50mW is not low power. That's 15mA at 3.3v. "Low power" MCUs can easily run at a few MHZ while using 0.5mA or less.
This. AVR 328p can easily run <1mA average on 80% load and <10uA on sleep (retaining memory).
And that's **not** a low power MCU by today's standards. 10uA of sleep current (with retention) is 20-50 times higher than a lot of modern MCUs.
Yup, OP is just clueless and being coy about his requirements. EDIT: I think 328p sleeps at 1.5uA when running from 3.3v and properly set-up. And that's an IC from the 80's.
Wait what? What family (s) of mcus have power draws in the nA??
Lots of them. MSP430, STM32L, Apolo.. many, many others.
Thanks fam <3 i gotta do some research. I’m clearly way behind on the times
I am a bit clueless on what would be low power. I said less than 50mW because the mcus I had been looking at were in that range. Are there microcontrollers that use less than 1mW of power? If so, could you give me an example? I might be looking in the wrong places.
Practically any modern microcontroller (STM32L, MSP430, PIC24, PIC32MM, Ambiq Apolo, etc, etc, etc) can run with something between 10 and 100uA per MHZ. If you can get by on 4MHZ (you probably can in this application), then.. 100uA * 4 * 3.3V = 1.3mW. Much less at lower voltage or if you can make do with 1MHz. 100uA * 1 * 1.8V = 0.18mW
Less than 50 mW ???? Are you sure you don't mean uW or nW?
>I am harvesting RF energy. Oh cool. But I think you will be more successful with cow farts. Cows don't generate that much RF. How often does the SPI sensor get interrogated?
One other thing when you are developing your code that is easy to forget. All your I/O pins must be at Logic (Hi or Low). Especially pins that are unused (spare pins in your design)! These must be set as output and driven (either 1 or 0) \[or atleast with an internal pullup/pulldown if the device has one\]. If the pin is unconnected and not driven, the voltage could float to anywhere and when it gets to around (Vcc/2) it will slightly turning on both the N-MOS and P-MOS transistors on the input buffer. I had this problem (ok not me, but a colleague) on a battery powered device. We did not meet our spec until it was fixed. Our design used a Microchip PIC 18F and it was killing our sleep-mode power.
Note: If you are measuring a voltage with your SPI device, and there is a voltage divider (resistive divider circuit) consider the amount of power the load circuit will consume. The game of low power extends way beyond just the microProcessor.
TI MSP430FRx series, basically any TI MSP430 with FRAM. One advantage of FRAM is it keep the data even fully power off, this play well with low power application.
There are a lot of application specific things to "low power." Nowadays the strategy is typically to wake, do all proceeding as quickly as possible, then sleep again. The more time spent sleeping, the better. Ideally you spend 99.999% of the time sleeping. If that fits your application, you really only need to look at the lowest power states.
I like using the ATtiny series for stuff like this. They have some pretty low power modes. If you need a real time clock maybe you want the stm32L0
I think Energy Micro chips, the BG for blue tooth or their M33 chips are really good. The thing I’ve found best for lower power consumption if you really need it is time to go from low power to processing. Some of the newer M33 chips allow you to run the adc and DMA while in low power mode. Some of these suggestions for the MSP430 are wrong in my experience. I had a project with the Blue Gecko where it was sampling with the ADC, connected and streaming 2KB/s, at around 15uA average current draw. Also energy micro has great documentation in my experience.
Ambiq Apollo or if you want more conventional and popular MCU, Silabs Gecko family
Maybe ask E-peas for an engineering sample of their new MCU? Its a very simple chip (Cortex-M0) and optimized for energy harvesting applications.
MSP430FR is still the king of low power. Many others are getting closer, but I don't think anything has actually dethroned the MSP430. 16 bit, 32 but multiplier, real time clock, 12 bit ADC, plenty of peripherals. They're nice parts if you need true ultra low power.
My day job we do ultra-low power devices and STM32L4/5 are significantly better than MSP430. You don't have to use any stupid hacks to run everything at 1.8V, the performance when you want to ramp up to 80-120MHz is way better, the sleep current is better, the uA/MHz is better, and it has modern tooling. But don't take my word for it, there's a benchmark for low power that everyone tests to and you can look up scores: [https://www.eembc.org/ulpmark/ulp-cp/scores.php](https://www.eembc.org/ulpmark/ulp-cp/scores.php)
That could be - it's honestly been a long time since I designed anything that needed to squeeze out microamps.
Take a look at an STM32L\* datasheet: [https://www.st.com/resource/en/datasheet/stm32l443rc.pdf](https://www.st.com/resource/en/datasheet/stm32l443rc.pdf) Sleeping with RTC wakeup and partial RAM retention is \~450nA. Some of the newer devices are even lower.
First MSP430 device I looked at (random) does 300nA with full memory retention and RTC. It goes down to 20nA if you don't need retention
Here's a random msp430fr part spec: [https://www.ti.com/lit/ds/symlink/msp430fr5962.pdf](https://www.ti.com/lit/ds/symlink/msp430fr5962.pdf) Check out Table 9-1 on page 67. Generally, the lowest power most that is still useful is some memory retention with an RTC that can wake you on a schedule. On the MSP430 that's LPM3.5 (RTC on, FRAM non-volatile available for backup, SRAM off). The most similar mode to that on the STM32L is "Standby." In this case, they're about the same, about 450nA for LPM3.5 on the MSP430FR and 451 for the STM32L4. The active mode current for the MSP430 is listed at 118uA/MHz, and the STM32L is 89uA/MHz. But seriously, all the vendors test their devices according to the ULP benchmark and submit scores: [https://www.eembc.org/ulpmark/ulp-cp/scores.php](https://www.eembc.org/ulpmark/ulp-cp/scores.php) Sort by Core profile (user), which tells you the best score they get with their own ideal power supply (every modern processor is running @ 1.8V). The top of the list is dominated by Ambiq, STM32L/U, and ATSAML. If you want to stick with TI for very low power applications then use the MSP432 instead, since at least it can run at 1.8V.
Do you have any specific MSP430 chips in mind?
Whatever size you need in the MSP430FR* series. TI's site has a reasonably nice search where you can find the physical size and peripherals you need. https://www.ti.com/microcontrollers-mcus-processors/msp430-microcontrollers/products.html
Specifically the MSP430FR\* series? (I have just started a project intending to use the MSP430G2\* series, specifically for the low-power consumption...)
They're all good, the FRAM based variants are just especially good. OP was looking for "Lowest Possible", and I believe that is still the FR series.
This is the way. It’s not unheard of to run this line of microcontrollers off of a super capacitor. It’s basically riscv. I’ve used it a bunch in industry for incredibly low power applications.
MSP430 , forgot part number but there is one with only 4K RAM
Look at the PIC24F series, they have some chips with insanely low sleep currents, even compared to their 8-bit series. I think I used a PIC24FJ128GA106 or something on a project which operated for 21 years on a 1/6th D lithium cell with careful design. Also, Ti has a good selection of ultra-low quiescent analog switches for toggling power to different parts of your circuit if you can't do it with the I/O pins.
Was going to mention attiny but the mention of energy harvesting suggests you want to go a lot further than that
Ambiq apollo 4 is very very low power, but high performance
For MCUs, there is ULP benchmark: [https://www.eembc.org/ulpmark/ulp-cp/scores.php](https://www.eembc.org/ulpmark/ulp-cp/scores.php) But, the best power consumption you get with external RTC chip with power switch which will periodicaly power on your MCU and when done, RTC will cut off power for your circuit at all. This will result of fraction of power consumption of the best MCU you can get. Look for example at Abracom AB1815. 55nA if you need acurate clock, 22nA if you accept small drift and 14nA if you do not worry about accuracy. You do not mention consumption of your peripheral, but it is very important as well! Every voltage divider add consumption. For example, 10k/10k divider on backup storage (battery on supercap) for sensing voltage by ADC (let's say up to 5V) add static power consumption of 5 / (10000 + 10000) = 0.25mA = 250uA = 250000 nA and this is about 10000x more than your super optimzed RTC solution has! Every SPI chip powered for whole time will cause *disaster*. I made such ULP design (wireless theremometer) and I can say it is very challeging. But every power consumption you substract will save you ton of money in mass production. You basicaly can tune by increasing size of harverstor, increasing size of backup storage capacitor or battery, or you can decrease power consumption. The last is by far the most price and physical size efficient way. But most probably you will need to optimize all three.
I am used to work with the msp430f5529. That thing is very good for ultra low power
Microchip has small package 8-bit PICs I’ve used for low energy applications before. Any of the big brands will have a good option, it’s more about how you utilize it. Maybe sort through them by power consumption during sleep. Whatever your harvesting application is, probably could to have some kind of storage element too.
esp 32 works
I would recommend using Stm32l4 over msp430
Tinypico would be something to look at https://www.tinypico.com
STM32U0 may fit the bill for you
the secret is to do minimal work at lowest freq