EEVblog #831 - Power A Micro With No Power Pin!

In this Fundamental Friday Dave will blow your mind as he shows you how you can power a microcontroller *without* a power or ground pin!
A potentially big trap for young and old players alike.
This is not something you'd normally get taught.
Can you guess how it's done before the secret is revealed?

SPOILER:
A tutorial on how ESD protection diodes in chips work and how they can be used, mostly inadvertently to power a chip through the input and output pins without having the power or ground pin connected.
This example uses an MSP430 microcontroller, but is applicable to almost any complex or simple CMOS chip.

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[Emtron_Technologies]

3 years I'm wondering "why it is so", when I am working with PIC uC. With this interesting tutorial, it clears very thing. Thanks Dave.

[BulletMagnet]

Diodes Inc. datasheet not telling you about the diodes.... YOU HAD ONE JOB!

[envisionelectronics]

The company for whom I work has a product that I found to have this error. I mentioned it in a engineering review for a new version of the board and was nearly thrown out of the room because "it works fine, you're wrong." Well, I wasn't wrong and I got a promotion out of the deal.

[jaa]

Do not lie to us Dave. We know you have a batteriser plugged in behind that piece of paper

[lmiddleman]

Another common case where this crops up... if your circuit has multiple power domains, like a battery-powered device where some chips get powered down and others remain powered up [soft-off], you have to worry about I/O between the domains. A logic high signal fed into an input on a powered-down chip will burn current through the protection diodes, especially when powering down a chip effectively ties its VCC to GND rather than floating it like your example.

[SaNjA]

Thank you so much, Dave!!! You've literally saved my project! I've been looking for the current leakage path for about a year, ant it turned out to be this effect! Unbelievable!

[AJ-kjgo]

You did it Dave! Over unity! That's a bobby dazzler

[CoolerQ]

Within the first 5 seconds, I said to myself "protection diode", and then I had to wait 8 minutes to confirm it. Dave, you missed a golden opportunity here to release a short video! :)

[tomsparklabs]

What I like about these videos is that there is no background music, giving you the freedom to add your own.

[PyroShim]

This is why I watch this channel! Best video ever. Always great to learn from an experienced professional.

[ewliang]

lol the part where he says you can remove the ground pin too. Learned something interesting and new to me today by watching this video. +1.

[CapnCoCo]

Thanks for the explanation. I actually stumbled onto this concept a few days ago while playing with some 74HC595 shift registers attached to an Arduino. I pulled the Vcc pin and was baffled to see my circuit still working. Couldn't find a proper explanation other than people calling is parasitic current from the other pins. Your explanation is much better and logical.

[TrebleWing]

I'm really glad you went deep into this explanation. I have been level translating 5v to 3.3 using mosfets for some of my applications, and now I will experiment with just using current limiting resistors! ((5v - 3.3v) - 0.6v) / 1mA! Easy!

[bikingmnviking]

excellent vid... just found you and based on this alone I'm subbing because you both know the material and have *such a passion for the material* you tend to ramble on which of course reminds me of my best professors back in avionics (& really in any field)... the kids in the group could get a seriously awesome free education from watching your vids alone, I'd gather. wow, 3.3 v and hct -- its advanced so much since I was taught the stuff I'll even have to look up the T.

My father taught electronics back in WWII and actually got a radiation classification from standing on hiroshima 9 months after the bomb went off. He instilled a great love of math and electronics and lots of fields in me. I look forward to more of your vids when I have the time.

[drcobol]

Julius Sumner Miller - one of the greatest physics teachers to ever be filmed. Loved watching his shows when they were on air here in America. Your videos are also great, Dave and kepp 'em coming!

[ASilentS]

Prof. Julius Sumner Miller and physics is his business. Respect.

[malgailany]

Really mind blowing facts!
I've witnessed some of these phenomena without being able to find suitable explanation for the situation.
Great video, thanks Dave.

[RicardoRfiles]

You could even power the microcontroller with only some Leds and shine some light on it. The LEDs can act as solar cells if you put a few in series.

[Shamino]

Thanks much! I don't build a lot of circuits, but I have built enough to find this video very educational. I learned something new today.

[PhattyMo]

I knew what this video was going to be about, before I even clicked it. I discovered this a while ago, with the MSP430 chips/launchpad board. I could disconnect everything but the serial lines, and it was still going. Or disconnect the serial lines, and leave the test/reset connected, and it would still run. The LED's were very dim, but they were still blinking/fading. These chips will run off of flea-farts, for power. All it takes is one LOW-ish pin, and one HIGH-ish pin, and they'll run. It was a head scratcher, for a minute.