IC output current question - datasheet

[banedon]

Hi guys

I have a newbie question on reading datasheets.
I'm planning to do some bread board tests with a T.I. SN74HC259N (8 bit addressable latch) and want to drive an LED on each of the Q0-7 outputs.
Checking the datasheet it seems to state the following:
(page 4) Continuous output current ... +/-20mA
(datasheet found on this page: http://www.farnell.com/datasheets/1886232.pdf)

Does this refer to a 20mA per pin current output maximum or is it for the entire outputs put together? I suspect the former, but would like to be sure (assuming that I'm looking at the right part of the data sheet!).

Many thanks for any advice given

[JohnnyBerg]

Page 4 also says: "Continuous current through VCC or GND . . . . . . . . . .. . . . . . . . . . . . . . . . . . . ±50 mA"

I am not sure the output can realy drive 20mA, as page 1 says: "High-Current Inverting Outputs Drive Up To
10 LSTTL Loads" and "±4-mA Output Drive at 5 V"

I think the 20mA is the max output clamp current, that is something completely different

As it is a TTL device, and you hook up the leds from the output to VCC (with series resistor), and do not exceed 4mA per LED, you should be fine.

[banedon]

Hi

Thanks for answering my question.

I had 2mA @ 1.9V from each line in mind (so the series resistors would be 1K5). I initially wondered about the 4mA in the main page, but then saw the other setting  .

Thanks again for your advice.

[Zero999]

The absolute maximum current through each output pin is 25mA. It's not a good idea to exceed this and the outputs will certainly not give valid logic levels with this amount of current being sunk or sourced from an output. The maximum output current you can draw, whilst still outputting a valid logic level (this isn't listed on the datasheet you've linked to but is standard for 74HCx) depends on the power supply voltage, at 5V it's 4mA.
http://www.nxp.com/documents/user_manual/HCT_USER_GUIDE.pdf

The absolute maximum current through the VCC and GND pins is 50mA.

Irrespective of the above requirements; you need to make sure the IC doesn't overheat due to excessive power dissipation.

[banedon]

2mA was more than enough. See attached pic & schematic.
Thanks for your advice.