SN74AHCT14: About interface level

soichiro kikuchi

Prodigy 250 points

Part Number: SN74AHCT14

Tool/software:

Can SN74AHCT14 be recognized as Low in this combination?

In fact, is Output of SN74LV240 less than 0.55V? (IOL should be much less than 16mA)

4 months ago

0 Clemens Ladisch 4 months ago

Guru 317000 points

The input current (I_I) is nearly zero, so the output voltage will be nearly zero. See [FAQ] What is the output voltage (VOH or VOL) when the output current is X or the supply voltage is Y?

0 Malcolm Lyn 4 months ago

TI__Mastermind 26150 points

Hi Soichiro,

Clemens is right. Refer to the FAQ for more details, but a summary is that the output voltage of a CMOS driver is determined by ohms law. Therefore the voltage won't be high enough to cause a transition on the AHCT device.

Best,

Malcolm

0 soichiro kikuchi 4 months ago in reply to Clemens Ladisch

Prodigy 250 points

In the example, VOH is calculated, but in the case of VOL, Rout×IOL means that the voltage will be higher than GND, right?
If I want to skip calculations. If IOL=100μA, can I use VOL=0.2V?

+1 Malcolm Lyn 4 months ago in reply to soichiro kikuchi

TI__Mastermind 26150 points

Hi soichiro,

The 100uA currents are typically not very accurate test currents by which to make a measurement. You can use 0.2V to estimate the worst case, but in reality if you had 100uA at the output, I would expect the output voltage to be very close to GND.

Best,

Malcolm

0 soichiro kikuchi 4 months ago in reply to Malcolm Lyn

Prodigy 250 points

Hi Malcolm,

Thank you for answering. It seems that Ican use that value when thinking roughly.

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SN74AHCT14: About interface level