SN74HC164A: SN74HC164A output current

Yuting Li

Part Number: SN74HC164A
Other Parts Discussed in Thread: SN74HC00

Hi team,

My customer wants to use SN74HC164A to directly drive LED. The output current is about 10mA. It recommends that the HC device output current is less than 5.2mA. What would happen if the output current is about 10mA? Will it influent the Voh or Vol? Is there any risks? Thanks.

over 2 years ago

0 Emrys Maier over 2 years ago

TI__Guru* 96591 points

Hello,

Please take a look at this FAQ for details on how to estimate the output voltage under different load conditions: https://e2e.ti.com/support/logic-group/logic/f/logic-forum/742466/faq-what-is-the-output-voltage-voh-or-vol-when-the-output-current-is-x-or-the-supply-voltage-is-y

Let me know if I can be of further assistance.

0 Yuting Li over 2 years ago in reply to Emrys Maier

TI__Intellectual 1420 points

Hi Emrys,

Thanks for your reply. Just double confirm, is it ok for HC device to output 10mA current if the low Voh can be accepted?

+1 Clemens Ladisch over 2 years ago in reply to Yuting Li

Guru 243980 points

Yes. The typical behaviour with a 5 V supply is shown below, but there are no guarantees for the worst case.

+1 Emrys Maier over 2 years ago in reply to Yuting Li

TI__Guru* 96591 points

The curve Clemens showed is very helpful for estimating the VOH and VOL of the device -- additionally, you should keep your output current below 25 mA, as indicated in the datasheet:

0 Yuting Li over 2 years ago in reply to Clemens Ladisch

TI__Intellectual 1420 points

Thanks, the figure is helpful.

0 Yuting Li over 2 years ago in reply to Emrys Maier

TI__Intellectual 1420 points

Got it. Thanks for your help.

0 Yuting Li over 2 years ago in reply to Clemens Ladisch

TI__Intellectual 1420 points

Hi Clemens,

I also have some question about this Figure.

What does the output current and output voltage mean? Is it the SN74HC00 output?
What is the different for these two line?
Is the output current is the sum of 8 channles?
Why does the voltage can be 6V when the supply is 5V? Thanks.

0 Emrys Maier over 2 years ago in reply to Yuting Li

TI__Guru* 96591 points

The curve that Clemens showed is called a 'curve trace.'

It is testing a single output pin from the SN74HC00.

The test has two steps, each of which produces a unique line:

first you set the input low, then sweep the current from -200mA to +200mA

second, you set the input high and repeat.

The machine that is forcing the output current is independent of the supply of the device. It measures the output voltage during the sweep and records the value of voltage for each current that it forced.

Note that the values on this chart go beyond the absolute maximum ratings of the device. You should always follow the datasheet abs max table when it comes to maximum values -- this sweep is just informative - it is not a guarantee of performance.

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SN74HC164A: SN74HC164A output current