Looking for Low current deep sleep MCUs - Page 1
Forum section: electronics / general

author: JPortici
author_rank: Super Contributor
timestamp: June 28, 2017, 10:31:53 am
content: Hi,I have to redo a remote because the transceiver has gone EOL and no pin to pin replacement is there.New transceiver has been selected, this would also be a good time to change the MCU.In this application the remote is in sleep for most of the time, and exchanges data with another gadget at the press of a button or in "active" modes.there are three modes:- Active connecting, 4 second sleep, 60ms active- Active connected, 32 second sleep, 60ms active (this is the mode the remote will be the most. average current from the transceiver is 6.024/21.61 uA best/worst case scenarios)- Idle, 256 second sleep, a couple of ms active just to occasionally check battery then go back to sleepPressing a button will put the remote in "Active connecting" modeDuring activity current is dominated by the transceiver, but during sleep current is dominated by MCU.Current MCU is a PIC16LF1823, chosen because i know it quite well... and it has a very low deep sleep current (in this case it is called "power down" in the datasheet, whereas for other families/brands with power down RAM power is removed, deep power down only way to exit is pulling a pin high/low)I'll Assume i can trust the datasheet.1823 has a Power down current + WDT (to exit from sleep) of 530 nA, says the datasheet (3.0V, 25°C). I can confirm it's in this ball park for all tested units during developement and production.However, working with this chip is a pain in the butt, very little Flash/RAM.Solution #1 is to scale up to 1824 or 1825 (increase flash/ram), make the code a little less hand optimized but more readable and call it a day.Solution #2 is to choose a different MCU with low cost, low pin count (max 20 for TSSOP, max 32 for QFN) and a power down current in the same ballparkWhat i've looked at for now:From Microchip:- Other PIC16: LF15325, LF18324. Basically, updated cores/peripherals. A bit more flexible, also for power managed modes but datasheet is still "Preliminary" with incomplete data. More than one year ago i rejected them for the same reason. sigh.- only other family that had all the requirements (low cost, low pin count, low power down current, SPI and ADC) was the PIC32MM. this boasts 520nA typical power down current + WDT. Other plus would be easier programmingFrom NXP:- LPC1111FDH20 has a very high deep sleep current, 6 uA. 220nA for deep power down and 4 always on registers (enough to save all the variables needed). Problem, with DPD only way to wake up the MCU is to pull the wake pin. The new transceiver doesn't have a low power oscillator and automatic wake up like the old one so i can't use this mode. pity.- LPC822M101JHI33 is probably the only good candidate i found: seep power down with wake up timer, 1.1uA. Still very high, but apparently less variations across temperature rangeAnd that's it. I didn't find anything else, that's a very short list. I accept suggestions- I checked out some ATTiny or SAM parts but power down currents were way higher. Same for STM32 L0- I'd avoid having to learn another family for this (8051, MSP, ..) unless i have better resultsSuggestions?

author: danadak
author_rank: Super Contributor
timestamp: June 28, 2017, 10:48:30 am
content: Possibly this -http://www.cypress.com/file/45776/downloadRegards, Dana.

author: MosherIV
author_rank: Super Contributor
timestamp: June 28, 2017, 10:57:17 am
content: I think the LPC1111FDH20 from NXP covers the ARM Cortex M0 series.Maybe look at another chip vendor for something more suitable, ST Micro :http://www.st.com/en/microcontrollers/stm32f0-series.html?querycriteria=productId=SS1574Also, do not avoid 16bit micros. I believe the good old MSP430 from TI is exceptional for low power and because they are going out of fashion, TI are making them cheap now.

author: JPortici
author_rank: Super Contributor
timestamp: June 28, 2017, 11:10:28 am
content: Thanks dana, Only PSOCs in pricerange seems to be PSOC4s, datasheet says 2uA deep sleep current. not that goodAgain, I looked at the STM32L0 family. sopposedly the lowest power they make. not so low power, unless i read the datasheets wrong, or they made it hard to understand (wouldn't be their first time)Remember i'm not looking at LOW POWER in running mode, but only at deep sleep and power down modes! it's being hard for me to find something as low power as pic16 in that aspect

author: alm
author_rank: Super Contributor
timestamp: June 28, 2017, 11:13:17 am
content: I second the MSP430 suggestion. Should be a nicer architecture and more flash than the 8-bit PICs. Something likethis partshould be able to handle everything in low power mode 3 (0.5 uA typical) and is available with up to 16 kB flash / 512 bytes RAM. They will probably be more expansive than the PIC16, however.EDIT: An alternative would be to use an external watchdog timer (likethis one) together with any MCU that can do a very low power deep sleep with wake up from pin change interrupt. For example, that MSP 430 would be down to 0.1 uA typical plus 35 nA typical for the watchdog timer.

author: TK
author_rank: Super Contributor
timestamp: June 28, 2017, 11:18:59 am
content: Quote from: alm on June 28, 2017, 11:13:17 amMSP430 is a nice option, and they are available in DIP package

author: jwm_
author_rank: Frequent Contributor
timestamp: June 28, 2017, 11:25:24 am
content: Msp432 is the msp low power design with an arm core. But msp430 is not bad at all, it's right in a sweet spot where 16 bits makes sense.

author: JPortici
author_rank: Super Contributor
timestamp: June 28, 2017, 11:36:54 am
content: Reading through the MSP430 manual..MSP430FR2111 - seems like LPM4,RTC,VLO is what i'm looking for. 590nA @25°, 3.0V. Basically on par with PIC16 XLP, not bad at allstill 2x the price of the pic in the quantities i'm looking forward to get, but it's a good excuse to get a launchpad devkitCorrect me if i'm wrong: with this mode i would- Put data to keep in FRAM- Go to sleep- With RTC event MCU restarts- Bit (saved in fram) tells if i have to do full initialization of transceiver or skip to programis it correct?

author: Yansi
author_rank: Super Contributor
timestamp: June 28, 2017, 11:56:15 am
content: You could also use STM32L0(Supply current in Stop mode well under 1uA at normal temperatures)

author: TK
author_rank: Super Contributor
timestamp: June 28, 2017, 12:09:24 pm
content: Quote from: JPortici on June 28, 2017, 11:36:54 amI am sure there are non-FRAM MSP430 chips at lower prices

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 28, 2017, 12:14:27 pm
content: Take a look at the recent PIC16F15xxx chips - lots more memory and a lot cheaper.

author: dgtl
author_rank: Regular Contributor
timestamp: June 28, 2017, 12:16:06 pm
content: Silabs (former Energy Micro) has been targeting the low-power segment. If you are looking for ARM uc-s, then check for their stuff as well. In addition they advertized nice energy profiling tools, that measure system current correlated to program trace, so you can optimize the higher consumption parts. Didn't check the current consumption numbers, though.

author: JPortici
author_rank: Super Contributor
timestamp: June 28, 2017, 12:35:42 pm
content: I checked again the L0 manual but it seems i can't exit stop mode with the watchdog/RTC event. Please, correct me if i'm wrongQuote from: TK on June 28, 2017, 12:09:24 pmI sorted for minimum price, that was the first one that ticked all the boxes@mike, 16f15xxx and 16f18xxx are on my list even though their datasheet is still incomplete for electrical characteristics. IIRC difference between the two for what i care about is in HEF vs EEPROM and thus slight difference in price (< 10 cents at low quantities, <5 cent in higher quantities)RE: EMF chips.. well, i'm going to use a silabs transceiver. I did check the EMF arm chips (also because i wanted to use on with integrated transceiver at one point) but i found the documentation really hard to interpret/understand, harder than ST if you can believe it, i got a bit put off. Too bad because chips are really promising

author: alm
author_rank: Super Contributor
timestamp: June 28, 2017, 12:38:47 pm
content: What about the external watchdog in some tiny package? Do not want the extra BOM item? Could turn out the be cheaper and lower power than getting a more expensive micro that has a watchdog timer that works at a sufficiently low power level.

author: Yansi
author_rank: Super Contributor
timestamp: June 28, 2017, 01:26:07 pm
content: Quote from: JPortici on June 28, 2017, 12:35:42 pmYes it of course can be waked up by RTC from stop mode. That is the purpose of the RTC Alarm function. Watchdog can also wake it up.

author: MosherIV
author_rank: Super Contributor
timestamp: June 28, 2017, 01:34:13 pm
content: QuoteCheck again, there are 3 low power modes. I had to double check and I agree with JPortici.The table says that only an external IRQ will wake the processor from STOP. Probably because in STOP mode the ARM core and all peripherals are no longer being clocked!Another gotcha about stop mode is that the processor pretty much wakes up and has forgotten where it was when put to sleep, ie like waking up and booting up again, so the code has to check if it is waking from STOP modeI have never had to use this STOP mode before only the first level of low power.

author: Unknown
author_rank: Unknown
timestamp: June 28, 2017, 02:09:19 pm
content: In addition to the MSP430 you might take a look at theSilabs EFM8 "Sleepy Bee."Up to 4k RAM, 64k flash. Minimum 50-80nA sleep mode consumption, depending on peripherals and supply voltage. Wakes up from sleep on:RTC eventsPort match eventComparator rising edgeIt can also be stopped / reset for less power draw, with the GPIO retaining state. Data sheet:http://www.silabs.com/documents/public/data-sheets/efm8sb1-datasheet.pdf

author: JPortici
author_rank: Super Contributor
timestamp: June 28, 2017, 02:18:06 pm
content: yep, since RAM is being powered off exept for the five registers in the always_on domain, only thing the mcu can do is do a reset.checking for reset from stop could be done by putting data on the always_on registershopefully they are cleared on a POR to start from a known state, but with STM and their manuals... who knows? do they actually write POR values now in the manuals?ah, i should end the rant because i wouldn't be using it anyway, adding an external chip to a costlier chip, on a tight bom an board is nonsense.Only two chips that seems to make it are PIC16, which already works, and msp430. i was looking if i could achieve same low power down / stop / whatever this manufacturer calss it power and eliminate some of the headaches.. not adding new headachesthe more i look into it the more i think i'll just go with a pic16 with more memory and more relaxed programmingjust excecuting sleep instruction halts the processor and the internal clock, power goes down to some tens of nA. Then WDT is separate and can be enabled so LPWDT is a couple hundred nA with sufficient accuracy, at WDT event clock starts again and after it stabilyzes code resumes excecution from last instruction. ram retention voltage is 1.5V, the whole thing can't operate at less than 2.3V so no problems. as simple as that

author: Yansi
author_rank: Super Contributor
timestamp: June 28, 2017, 02:21:36 pm
content: Quote from: MosherIV on June 28, 2017, 01:34:13 pmI know what I am saying. You shall look again, not me. (The RTC generates events for the EXTI controller. Reference manual RM0377, chapter 22.5).

author: suicidaleggroll
author_rank: Super Contributor
timestamp: June 28, 2017, 02:31:07 pm
content: Quote from: JPortici on June 28, 2017, 02:18:06 pmYou don't have to go to LPM4...LPM3 should be more than sufficient. It still keeps ACLK and the crystal active, which you should be able to use to drive a timer to wake back up. The simple msp430g2553 consumes 500nA at 1.8v in LPM3. That's 900nW...it would take 127 years for that to drain a single 1 Wh AAA. How low do you need to go?

author: MosherIV
author_rank: Super Contributor
timestamp: June 28, 2017, 02:57:05 pm
content: QuoteFair enough (and my apologies). Another case of the reference manual contradicting itself.The table in the Power Control section clearly states that Stop mode "HSI andHSEoscillatorsOFF"Which to me means that the RTC external clock is switched OFF, so the RTC should not be running.Guess someone will have to try it to see which part of the ref manual is correct.Like I said, I have not tried the STOP low power mode.

author: JPortici
author_rank: Super Contributor
timestamp: June 28, 2017, 03:11:45 pm
content: Quote from: Yansi on June 28, 2017, 02:21:36 pmYou are right! I don't know why i understood that i couldn't run the LSI oscillator in stop mode(and when i wrote that i had JUST read both the datasheet and the reference manual)

author: krho
author_rank: Regular Contributor
timestamp: June 28, 2017, 03:56:38 pm
content: QuoteI don't know what you were looking at but STM states the following for STM32L072KB0.29 ?A Standby mode (3 wakeup pins)0.43 ?A Stop mode (16 wakeup lines)0.86 ?A Stop mode + RTC + 20 KB RAM retention

author: Yansi
author_rank: Super Contributor
timestamp: June 28, 2017, 04:10:06 pm
content: Quote from: MosherIV on June 28, 2017, 02:57:05 pmWhy would you run RTC in yourlow powerapplication from HSI/HSE in the first place?RTC is kept running from LSI (internal RC) or LSE (crystal).There is none contradiction in the RM in this case.

author: MosherIV
author_rank: Super Contributor
timestamp: June 28, 2017, 04:29:33 pm
content: QuoteYes, sorry my mistake.Was not paying attention, busy doing the day job.

author: wraper
author_rank: Unknown
timestamp: June 28, 2017, 04:32:00 pm
content: Quote from: Elf on June 28, 2017, 02:09:19 pm+1, in addition it has decent free IDE and cheap dev board.http://uk.farnell.com/silicon-labs/slstk2011a/dev-board-efm8sb20f64g-sleepy/dp/2469341which has built in J-link debugger, can be used for programming/debugging external device as well.EDIT, it also has 2% precision internal oscillator which might be useful in this case. Also silabs MCUs are very cheap as bonus.

author: danadak
author_rank: Super Contributor
timestamp: June 28, 2017, 05:03:21 pm
content: If you look at stop mode you can get down to tens of nA at room temp,hot ~ 1 uA. Note startup time from stop mode is 2 mS. Startup timeof course impacts avg power consumption in LP designs,http://www.cypress.com/file/121271/downloadRegards, Dana.

author: snarkysparky
author_rank: Frequent Contributor
timestamp: June 28, 2017, 08:06:13 pm
content: PIC24F04KL series.