Electrical Characteristics

What part don't you understand? these are the current limits...

http://www.atmel.com/Images/2490S.pdf

I understand this is a current limits..

I am running my MCU (atmega64a) with LDO regulator which has a output current of 150mA, but the datasheet of controller says that dc current b/w vcc and gnd is 200ma-400ma, If this is the case my controller will not even work with min current?? but in actual my MCU is running well.

so my question is whether this current limits are only with certain conditions or the operating current of MCU?

I believe those are the design limits..

Within your design, the max load current (400mA) of the part should be considered. A more robust LDO would be a start. The I/O sink/source current limitation can be overcome with the use of an external transistor or a buffer depending on the number of I/O's. The greater number of I/o's would push one toward a buffer part where real estate is at issue. Again the source power supply should be capable of supporting the max possible load current or you run risk of damage as stated in another reply. The LDO appears to be your initial weak link, solving that issue gives you more options. The other solution is to be sure that the part does not draw >150mA with all I/O's sourcing. You can get LDO regulator in the 50mA-500mA range. It's assumed this is a batt operated or portable device.

i think he means the sinking and sourcing of the I/O ports if all the ports output at the same time(source) it may not exceed 400 mA

when all the I/O ports are set to input at the same time the maximum sink current may not exceed 100 mA.

The CPU logic itself uses maximal 20 mA

Thanks for reply,

I am using some 6 pins which sinks more current,

2 adc pin for led

1 pin for gsm ring

1 pin for audio sbt

1 pin for motor start

1 pin for motor stop

so, now as per the datasheet if any one of these pin exceed 40mA ,then it will not work?? right!!

Well it might work for a time, but you risk damage...

never use a port to directly drive something, use a transistor, fet or opamp to take the load of the CPU.

Those are absolute maximum ratings.

Read the note to the right in the data sheet.

You don't say how you are using the MCU, but I would expect the actual current consumtion to be way below those values.

Typical current drawn by the core is only 20 mA at 8 MHz, add to that what your peripheral circuits are taking, and what you are asking the MCU to source (no more than 20 mA per pin with a 5V supply) and you should find that your LDO is more than adequate.

As Ekpe says, don't drive high loads directly, always buffer.