Confirmation of Current ratings on ATtiny4313

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#1
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Hello, bit of a noob questions. May even belong in general electronics forum. Just needed to confirm I'm understanding the data sheet correctly, don't want any blue smoke !

The ATTiny has:
DC Current per I/O Pin:40.0 mA
DC Current VCC and GND: 200.0 mA

but in the fine print (notes 3 and 4) it says:
The sum of all IOL, for all ports, should not exceed 60 mA.
The sum of all IOH, for all ports, should not exceed 60 mA.

I'm not clear if this is a combined maximum (all source+all sink <=60ma) or is it (all source+all Sink<=120ma as long as each is less than 60ma). I guess you could also read it as maximums per PORT.

I'm multiplexing a bunch of LED's (as a learning exercise)setting the appropriate PORTBx high and PORTDx low.

Each LED is being sourced and sunk (?) through the chip.

ie. Assume my LED's draw 20ma ea. would that mean I can only turn one on at a time ? (1x20ma source+1x20ma sink) or can I do 3 (3x20ma source+3x20ma sink)

Further, the datasheet indicates that these maximums are for steady state conditions. Since I'm cycling through at 4Mhz does that mean I can push them closer to the chip max of 40ma/200ma ?

Thanks in advance.
Marc

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No RSTDISBL, no fun!

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Also, use current limit resistors and ignore those who say they are not needed. Learn to do it right in the first place.

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Brutte wrote:
Related problem.

Thanks, although after reading through that I'm not entirely sure what the answer is ! Sounds like some room for interpretation, which you wouldn't think there should be.

I would think with the chip max at 200ma that you should be able to source 60ma and sink 60ma that would yield 120ma of the absolute max of 200ma. Otherwise you could only use 60ma of 200ma which seems odd.

Probably won't be driving anywhere close to that for this learning project, just trying to understand as much as I can.

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I submitted the questions to Atmel. Here is their response:

The total current should be: all source+all Sink<=120ma as long as each is less than 60ma.

The total sink current must be less than 60mA and the total source current must be less that 60mA.

They are different current loops

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A multiplexed display for a desktop does not need massive currents. You can source/sink from the AVR.

A medium display can have segments direct from the AVR.
The digits (common) need a ULN2803 or similar driver.

A high current display needs drivers for both segments and digits.

As you have discovered, the currents soon add up!
e.g "8." with average 2mA segment current is 16mA through the common pin.
If you are displaying "8.8.8.8", you have got 16mA*4 = 64mA for the digits and 2mA*4 per segment pin ( = 64mA total)

David.

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Quote:

If you are displaying "8.8.8.8", you have got 16mA*4 = 64mA for the digits...

Most would multiplex (as OP mentioned) such a setup. So then the *4 goes away, right?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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No, because the multiplex would do 8mA per segment for 25% of the time. i.e. 2mA average segment current.

Clearly a tiny4313 has to multiplex since it only has 17 GPIO pins available.

If you don't multiplex, you don't need to source current for the common pin. But you have an awful lot of segment wires.

David.