Electronic – What does “DC Current VCC and GND Pins” in ATmega8 datasheet mean

atmegacurrentmicrocontroller

I'm using for some DIY project ATmega8-16PU, during the reading of the datasheet

(Datasheet Revision 2486AA–AVR–02/2013 )

I've encountered in section "Electrical Characteristics – TA = -40°C to 85°C" parameter, which is called "DC Current VCC and GND Pins". Value of this parameter is 300mA. I was looking in Internet for some meaningful interpretation of this parameter. What I found was however a lot of confusion on the topic. Here are three possible interpretation of this parameter, can you please tell me, which one is the right one.

300mA is total current into all VCC and out of all GND pins.
300mA is current into all VCC pins and there is 300mA out of all GND
pins
300mA is current into each VCC pin and 300mA is current out of each
GND pin

The most reasonable explanation supporting last interpretation I found under following link:

Allowed current thru AVR devices

Depending on which interpretation is right one, I can e.g. change package type to TQFP in order to increase my current budget.

Please note that I don't want to exceed any Absolut Maximum Ratings, what I want however is to try out exceeding test conditions in datasheet.

Best Answer

To remove further confusion. There is only one Vcc pin.
AVcc is a different power domain only for the ADC Clock system and PORTC. Read the notes below the table.

This is the right answer:

300mA is total current into all VCC and out of all GND pins.

Related Solutions

Electronic – Using avr-gcc _delay_ms causes chip to freeze

I suspect the problem is not with your C code but with your Makefile.

The following lines in your Makefile produce an example.o object file.

main:
    avr-gcc -g -Os -Wall -mmcu=atmega328 -c ../src/example.c

The created .o file only contains the symbols and code from example.c, not the additional source required to actually make it run on a target system such as interrupt vector jump tables and code to initialise the BSS RAM segment to zeros, and load your initialised data sections.

You'll need to add an additional line something like this to run the linker and produce an output object suitable for download to the AVR part. Alternatively, use avr-ld, but you'll have to work out all the required linker options.

main.elf: example.o
    avr-gcc example.o -o main.elf

You can use avr-objdump --disassemble-all <filename> on both example.o and main.elf yourself to verify the different content of each file.

It's always a good idea to try to reduce your problem in steps to the most simple example possible. In this case, it would probably mean dropping into the AVR Studio software and creating a project running on the simulator using their managed build process. From there, you could them export the Makefile in use by their build process by using the 'Export Makefile' menu option. The generated makefile could then be compared with your version.

Actually, it's probably a good idea to use a Makefile similar to the one generated by AVR Studio because it has the correct rules already defined, you just have to set up some variables with regard to which objects need to be generated and the final target file name.

How to the Vss or Vdd pins of a MCU handle sink or source current

All this is saying it that the maximum current, either sinking or sourcing, is 150 mA for the entire chip.. This is probably dictated by heat considerations.

If you had all 51 GPIO pins drawing current, the average would have to be just under 3 mA (150/51) to avoid going over the 150 mA limit. (Actually you could nearly 6 mA per pin, if half were sourcing current and the other half were sinking. But that would be pretty unusual.)

But rather than limit each pin to 3 mA (or 6mA), the spec allows each pin to draw up to 25 mA. But if you have six pins sinking 25 mA each, then you have used up your total of 150 mA and all other pins must not be sinking any current (although they could be sourcing some).