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Rich Quinnell

Millivolt MCUs Emerging

Rich Quinnell
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Microp
Microp
3/6/2012 2:21:28 AM
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Low power MCU- a promising technology
Rich, such low power consuming devices have a promising future in MCU/Embedded world. In most of the high end devices/appliances energy harvesting is a major concern and such low power consuming chips can incorporate for a better durability.

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Rich Quinnell
Rich Quinnell
3/6/2012 12:23:55 PM
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Re: Low power MCU- a promising technology
Your mention of energy harvesting is right on the money. The people working on these near-threshold devices often refer to the ability to operate on a single solar cell as a feature of these devices. I presume that even under artificial lighting a cell can generate enough power to run one of these. Thus, anywhere that the users can see, these MCUs can operate. It makes for a tremendous application space.

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duanebenson
duanebenson
3/6/2012 12:48:16 PM
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Related hardware
Have you heard anything about any of the external components typically needed in an embeded system also operating on down near threshold voltage? I'm thinking about things like MOSFETs, LED, MEMs devices. I know there are a lot of level translation methods, but it would be nice to be able to keep the entire system down in the same low-power range.

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Ryszard Milewicz
Ryszard Milewicz
3/6/2012 1:09:13 PM
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Re: Related hardware
I do agree with Duane, we need low voltage peripheals. For example wireless sensor node: sensor, ADC, RF transmitter. Then all could be supplied using e.g. thermoelectric generator.

By the way, in MCP560x core works at 1.2V and I/O at 3-5V, but it is not very energy efficient processor.

 

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duanebenson
duanebenson
3/6/2012 3:39:53 PM
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Re: Related hardware
Some of the newer PIC processors, and of course some of the ARMs, operate down to 1.8V but I haven't built anything to run at that voltage yet. There is the peripheral issue and 1.8V is an odd voltage. The standard battery won't cut it and Lithium would require a regulator to drop the voltage. Barring a specific need, I don't see much point to 1.8V. 1.2 could get by with most single cell batteries, so that would make more sense.

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Rich Quinnell
Rich Quinnell
3/6/2012 4:28:45 PM
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Re: Related hardware
Duane, does that 1.8V need to be regulated? I would think that the MCU had its own internal regulator and that it would tolerate a supply voltage down to 1.8V but up well above that because if its internal regulation. Does the spec sheet show a broad range?

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duanebenson
duanebenson
3/6/2012 6:12:52 PM
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Re: Related hardware
One of the chips I've used, the PIC18LF26K22 can operate down to 1.8 volts. I don't see anything in the datasheet about a built-in regulator in that chip. The datasheet I have is still in preliminary state so there may be a bit on information covering supply that I haven't seen yet.

Some PICs do have internal regulators though. The PIC18F24J50 wants the core to stay at 2.5 Volts or less. It has an internal regulator for the core voltage allowing the I/O to be supplied with and operate at 3.3 volts. The data sheet notes that if the main input voltage drops below 2.5 volts, then the core will just follow operate at the supply voltage.

The ARM LPC1114 that I'm getting familiar with, doesn't show an internal regulator. The electrical characteristic charts show things like supply current on a continuous line from 1.8V to 3.6V. I'd interpret that to mean that any regulated voltage in that range would be fine. Some of the charts specifically call out different curves for 1.8V, 2.0V, 3.3V and 3.6V. Again, that would imply to me that it operates at any regulated voltage in that range.

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Ryszard Milewicz
Ryszard Milewicz
3/6/2012 7:23:56 PM
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Re: Related hardware
PIC18F24J50 has internal regulator while LF version doesn't and must use external.

I think LPC1114 has internal LDO because Vcc is explained in datasheet as "supply voltage to the internal regulator" and other ARM MCUs have LDO built-in.

STM32F1 internal regulator has output voltage 1.8V, STM32F2 and STM32F4 1.2V.

PIC32MX5xx/6xx/7xx internal regulator output is 1.8V typical. So if you use 3.6V power supply, 50% of input power is lost.


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Rich Quinnell
Rich Quinnell
3/6/2012 11:30:54 PM
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Re: Low power MCU- a promising technology
Microp, so what would you use such a low-power MCU for? The technology seems promising, but at the moment I am at a loss as to what would be useful to do if I could operate essentially without any power, even using energy harvesting.

Maybe we can turn the problem on its head, and consider applications where power is available but not voltage. A single AAA cell would have plenty of headroom to run one of these devices with peripherals. Further, it could run for a long time because it would not be dependent on the battery's terminal voltage being near its peak.

Any other suggestions out there? What could you do with an MCU that needed less than a volt in order to function?

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northstar
northstar
3/7/2012 6:25:22 AM
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Re: Low power MCU- a promising technology
Rich, here is a possible applications: sensors in garments: http://www.newscientist.com/blog/invention/2007/10/circuit-board-clothing.html

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