Best low-power MCU? - Page 1
Forum section: electronics / projects

author: 8086
author_rank: Super Contributor
timestamp: November 27, 2010, 03:16:27 am
content: Hi all,I'm starting a project that needs to be able to go into a low-power mode and wake up at set intervals. I like the parallax propeller but it seems to have quite high current draw even with PLL off and only 1 core running. I was wondering if anyone knew of a good PIC with minimum 10 I/O pins and very low current draw when configured correctly. Either that or some way to make the propeller not draw as much current. Needs to be SMD also.Of course I will be scouring the internet but if you know of any then let me know please, thankyou

author: oPossum
author_rank: Super Contributor
timestamp: November 27, 2010, 03:25:36 am
content: There are many PIC nanowatt XLP parts with RTCC that can sleep with less than 3 uA.How much code and RAM space do you need? Writing firmware in C? 5V or 3V I/O?http://www.microchip.com/ParamChartSearch/chartdetail.aspx?branchID=143&mid=14&lang=en

author: TheDirty
author_rank: Frequent Contributor
timestamp: November 27, 2010, 03:38:53 am
content: We would need more concrete numbers for what you actually need. Sounds like most popular microcontrollers with sleep or deep sleep modes would work fine for you. Doesn't sound like you need the heavyweight MSP430 or NanoWatt or Cortex-M0.

author: 8086
author_rank: Super Contributor
timestamp: November 27, 2010, 03:42:39 am
content: Thanks for that, I really like the look of the nanowatt XLP partsIn answer to your other q's: code and ram space really is unknown at this point, i'm just getting a basic outline of the project right now. firmware will be C, yes. 3v I/O.

author: oPossum
author_rank: Super Contributor
timestamp: November 27, 2010, 03:45:23 am
content: PIC24FJ64GB002 looks good64k flash (highest available in 28 pin package)8k RAMRTCC28 pin DIP, SOIC or QFNhttp://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en536121

author: Hypernova
author_rank: Unknown
timestamp: November 27, 2010, 05:52:49 am
content: Look into atmel xmega if you want lots of peripherals. You get :-up to 8 SPI, 8 UART, 4 I2C, 128K flash and 8K ram. You can also hook up external ram chip to get 16MB-4 DMA channels-24 128MHz PWM at 10bit resolution (how I use them to get 125KHz signal at that resolution, max is 16bit but you can chain them to get 32bit etc)-16 12bit ADC DAC. about 200+KSample/sTQFP package with internal 32MHz, 2MHz and 32.768KHz crystals for RTC. sparkfun has a break out. All the IO are also logically organized and easy to control. If you want to toggle a pin just do PORTA.OUTTGL = PINx_bm as one instruction, don't have to do read-modify-write. 3 level interrupts so you can do quad multi threading without using a RTOS.I know you wanted PIC's but it's always nice to look around.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 27, 2010, 10:32:39 am
content: Pretty much all current mainstream micros have low-power modes - XMOS is an oddball as it's targetted at high performance, not low power.The biggest difference you'll see is the power needed to run a timer to wake it up periodically - this can typically range from 10uA to below 1uA. Unless you're using small coin cells anything below 10uA is generally fine.A second important factor is how quickly it can wake up, do something useful and go back to sleep again - oscillator startup time is usually the most critical factor (also PLL lock time for higher-end parts like ARMs) , with RC oscs being orders of magnitude better than crystals or ceramic resonators. Many parts have 1% calibrated RC oscs, and at least one 0.25% (some PIC24s with USB), which is as good as a ceramic resonator without the startup time.The ability to switch osc types on the fly can also be handy - wake up on RC, check if anytyhing needs doing and only do the xtal startup/PLL time where necessary.The other useful capability is switchable clock speeds, for when you need to stay awake but not be doing much - the Nanowatt PICs are good in this respect.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 27, 2010, 11:34:28 am
content: Quote from: oPossum on November 27, 2010, 03:25:36 amthe nanowatt marketing is ok. why dont first check out the simpler pic (eg 12f629) that sleep down to 1nA at 2V. my project pic12f629@3.3V (power supplied from 23A 12V) put the pic down to ~2uA, will take a while b4 the 23A is degraded. the problem was not the pic spec (sleep current), but my own circuit design that draw too much power while the mcu is sleeping, almost blame the mcu, but it turned out its my own stupidity with the circuit design. took me a while b4 figuring that out. so the advice... dont just look at the mcu and try to crank the code to get low power and blame it if it cant reach your target/spec. the whole circuit design must be taken into consideration. my 2cnts.

author: Hypernova
author_rank: Unknown
timestamp: November 27, 2010, 11:54:02 am
content: Quote from: mikeselectricstuff on November 27, 2010, 10:32:39 amxmos doesn't really factor into this topic as it's not meant to be a microcontroller, more like embedded processors like Blackfin and Coldfire.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 27, 2010, 12:16:35 pm
content: Quote from: Hypernova on November 27, 2010, 11:54:02 ammaybe the idea is to rule out any more complex processors/mcus. i guess lowest powered mcu means the simplest featured mcu as you can get. or am i wrong?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 27, 2010, 12:55:45 pm
content: Quote from: shafri on November 27, 2010, 11:34:28 amNot with a wakeup timer running it doesn't.