What is max current on an AVR?

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sparrow2
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Posted by sparrow2: Wed. Feb 15, 2017 - 09:52 AM
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If an AVR can take max 40mA on each IO and max 200mA on VCC and Gnd pins.

 

This is simple when there only is one Gnd and Vcc, but for a chip with 3 Vcc and Gnd pins what is max current for the chip?

3x200=600mA

3x200-50=550mA (or something like that)

200mA because it's heat that is the problem. 

or ?

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AVR Microcontrollers, megaAVR and tinyAVR
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awneil
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Posted by awneil: Wed. Feb 15, 2017 - 10:02 AM
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Surely, the datasheet will specify this for the particular chip & package?

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sparrow2
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Posted by sparrow2: Wed. Feb 15, 2017 - 10:11 AM
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NO that is the problem! (Or I'm blind)

 

There is no chip info!

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awneil
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Posted by awneil: Wed. Feb 15, 2017 - 10:36 AM
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So which specific chip are you asking about?

 

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sparrow2
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Posted by sparrow2: Wed. Feb 15, 2017 - 10:53 AM
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Any!

No Atmel AVR datasheet have the information (perhaps Xmega)

 

But in this case it's a mega324

 

only info is under absolute maximum ratings

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awneil
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Posted by awneil: Wed. Feb 15, 2017 - 11:26 AM
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So it doesn't.

 

sad

 

Perhaps what I was thinking of was:

 

ATmega324P/V Complete  Datasheet; revision B, updated: 08/2016 wrote:

3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC =
3V) under steady state conditions (non-transient), the following must be observed:

3.1. The sum of all IOL, for ports PB0-PB7, XTAL2, PD0-PD7 should not exceed 100mA.

3.2. The sum of all IOH, for ports PA0-PA3, PC0-PC7 should not exceed 100mA.

Which gives you a maximum total of 200mA;  which corresponds to the value stated for "DC Current VCC and GND Pins" - so that would be the total for all Vcc & GND pins.

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sparrow2
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Posted by sparrow2: Wed. Feb 15, 2017 - 11:55 AM
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The real problem was because I was looking at the 324PB that have a max current of 100mA on the Vcc and Gnd pins.

It has 1 Vcc and 2 Gnd so does it mean that the amount of sink and source are different? 

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Posted by Torby: Wed. Feb 15, 2017 - 02:52 PM
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Even for 200mA, I think I'd use some little N channel mosfets.

 

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Posted by sparrow2: Wed. Feb 15, 2017 - 03:03 PM
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? the problem is the power for the hole chip. 

Like you can't run 24 5mA LED's direct! (I don't want 24 extra transistors, then I just stay with a 324P)

But if the two Gnd make it a total of 200mA that can run "into" the chip it would work (for this project I don't care about noise on the ADC). 

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Posted by gchapman: Wed. Feb 15, 2017 - 04:44 PM (Reply to #9)
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0.9V * 200mA = 180mW (max sink voltage and max sink current; somewhat warm)

The mega324PB comes in VQFN with an exposed pad to sink the heat.

 

"Dare to be naïve." - Buckminster Fuller

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sparrow2
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Posted by sparrow2: Wed. Feb 15, 2017 - 06:49 PM
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From #9

But I guess that I can put 12 LED's to Gnd and the other 12 to Vcc       (and 24 resistors).

Then it should be ok.

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