Operating Voltage Range

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If a chip (atmega32u2) says Operating Voltage Range (V) is 2.7 to 5.5. Does this mean using an external oscillator will remain constant in that range? That is to say 3.3 will not over clock it any from normal use with 5v?

Last Edited: Mon. Feb 12, 2018 - 07:59 PM
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A crystal, ceramic resonator or a TCXO will keep it's frequency. If you use some funky self-made oscillator, it might not. So you should be more scpecific for definite answer. The internal RC oscillator is quite stable but shows some dependency.
The operating range specifies that the device itself can be used in that range. If you go higher, you might damage it. If you go lower, it wont work reliably or not at all.
But you need to consider something else: while the voltage does not change the oscillator frequency, it changes the frequency compatibility of the device. At 3.3 V it can not run at 16 MHz anymore.

 

From the datasheet:

These are maximum speeds, not the actual oscillator frequencies!

 

Edit: changed the wording a little

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

Last Edited: Mon. Feb 12, 2018 - 08:43 PM
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I can understand this with the internal but was more curios with a tight clock like the txc Quartz (i.e 9B-16.000). My worry being usb timing. My experience with the mega 328 was that running it at 3 volts would force it to run faster and I want to ovoid that. Your opening sentence suggests there is no concern and that is what I was hoping for. Thx for the reply.

 

 

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S_K_U_N_X wrote:
My experience with the mega 328 was that running it at 3 volts would force it to run faster

 

That does not make any sense, please explain???

 

 

Jim

 

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ki0bk wrote:

S_K_U_N_X wrote:
My experience with the mega 328 was that running it at 3 volts would force it to run faster

 

That does not make any sense, please explain???

 

 

Jim

 

 

This was based on of this talk.

http://www.raphnet.net/electroni...

 

Specifically this talk

The dreamcast controller is powered directly from the USB 5 volt line. Communication with the controller is done at 3.3v so a regulator is required for the MCU. This simple design uses an Atmega168 running at 16MHz. At 3.3v, the documented maximum is around 13MHz, so the MCU is overclocked. This does not seem to cause problems, but eventually I might design a more complicated version with a level translator to do away with this practise.

 

 

Maybe his understanding is incorrect or I miss understood it?

 

Last Edited: Tue. Feb 13, 2018 - 03:49 PM
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S_K_U_N_X wrote:

Maybe his understanding is incorrect or I miss understood it?

 

The word 'overclocked' means that the user is running the chip faster than the specification allows not that the chip itself runs faster. See the graph in post #2, that shows the allowed combinations of frequency and voltage that the user can choose, to stay within the specification. Any combination within the shaded area is guaranteed to work; another combination outside that area and the chip may freeze/hang/glitch/die.

 

[E2A]

To expand on that...

 

1) The chip is not guaranteed to work at all below 2.7V. It might; it might not. As the voltage falls below that level, it is likely that parts of the chip, especially the memory, will start to malfunction.

2) The chip is not guaranteed to work at all above 5.5V. Above that voltage it is likely that the chip will burn out.

3) At 2.7V the chip is guaranteed to work at 8MHz.

4) As the voltage increases to 4.5V the frequency at which the chip is guaranteed to work increases to 16MHz.

5) Between 4.5V and 5.5V the maximum frequency stays at 16MHz.

 

Plenty of people have run chips outside of these limits, however, there is no guarantee the chip will work or even survive.

"This forum helps those that help themselves."

"If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

 

Last Edited: Tue. Feb 13, 2018 - 04:32 PM
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Ok, got it. Then running an external clock of 16mhz at a 3.3 operating voltage is not within the safe and guaranteed area. So I will need to regulate to a minimum of 4.5 to get back in a guaranteed operation.

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S_K_U_N_X wrote:
So I will need to regulate to a minimum of 4.5 to get back in a guaranteed operation.
For a one-off, home project you'll likely "get away with it". But if this is for a commercial design it would be very unwise to drive chips outside specification.

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S_K_U_N_X wrote:

Ok, got it. Then running an external clock of 16mhz at a 3.3 operating voltage is not within the safe and guaranteed area. So I will need to regulate to a minimum of 4.5 to get back in a guaranteed operation.

 

For guaranteed operation...yes.

 

Failure modes when operating outside the spec can be very subtle. It can be things like your flash (program) memory sometimes reading out the wrong opcode, or sometimes a counter will miss a step, or a RAM location will be corrupted.

"This forum helps those that help themselves."

"If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

 

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In this case those subtitles are not going to workout. Thc for the help.

 

Clawson, that opens up another topic.