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running under voltage and DCO interesting find.


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heys, in trying to answer a question in my head about DCO and voltage in.

 

the MSP430 chip can run at significantly lower voltages than listed in the datasheet depending on DCO.

I am using the G2553 PDIP package, but i don't think that would make a difference

 

at 16MHZ the datasheet lists 3.3V as the minimum required voltage, but my chip can run at 16mhz down to 2.2 volts. before it cuts itself off in reset.  and at 1 MHZ it runs down to 1.5V before it cuts out.  interestingly, the DCO speeds up slightly at the low voltage 

post-7036-0-69951000-1371965442_thumb.jpg

 

this testing was done based on watching the SMCLK output and also running a program turning an output pin on and off.

 

this may be useful to low voltage projects that can benefit from the faster clock rates.

 

just interesting stuff i guess.

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How many different chips did you tried this with?  I have had MSP430s (2211s, I believe) start to perform erratically at 3.0 volts when running at 16 MHz.

 

Remember, the datasheet only lists guaranteed parameters and some chips from some batches may perform substantially better than others.

 

It is also worth noting that the factory calibration values for the DCO are calculated at a specified voltage and the DCO will oscillate at a different frequency when the voltage is raised or lowered.  IIRC the nominal delta freq. as a function of voltage is even specified in the datasheet.

 

In my experience, the factory calibration values are not terribly accurate even at the specified voltage, and if DCO accuracy is at all important you should re-calibrate at the operational voltage.

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This is something I was wondering about recently.

 

 

How many different chips  I have had MSP430s (2211s, I believe) start to perform erratically at 3.0 volts when running at 16 MHz.

 

Can you give more details? I would like to work at 16mhz for some things but I am wondering what might go wrong if the battery gets too low.

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Interesting find, although not too surprising. For example, you can also apply over 450V to just about any 1210 ceramic cap and it will survive and "work" for quite awhile regardless of its voltage rating. Datasheet parameters are generally "typical" and "recommended" values. True failure points for components are generally not listed even in the "absolute max rating" sections of datasheets.  Its all about reliability, accuracy, and performance over temperature. My question would be @ 16MHz & 2.2V, is the frequency truly 16MHz? 

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according to the SMCLK output yes it is the blue line on the graph is the measured clock freq (by my oscilloscope) at those voltages.

although the DCO speeds up by about 2% as the voltage drops

 

My original intention was being able to run 16MHZ clock down to 3 volts, which it appears will work fine.  I just extended the testing set out of curiosity

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interesting, mine was with no real load on the MSP other than turning an output on and off, but there was no load on the output...  I'll test it again PWMing 8 LEDs

 

the video is uploading to youtube right now 30 minutes to go, it will be live at this link when its done  but I took the 8 LEDs on my board and flipped them on and off randomly to simulate PWMing them with a breakpoint at the start of the program to catch if it resets randomly.  My chip runs happily down to the same 2.2V at 16MHz clock.

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