SN74HCS00-Q1: Input Threshold and Quiescent Current

Josef Warta

Part Number: SN74HCS00-Q1

Hello Team, following question from customer:

- Ínput switching thresholds:

Vcc = 2.5V but our datasheet only shows data for 2V, 4.5V and 6V.

Spec for 2V is VT+min 0.7V (means 35%VCC) and VT+max 1.5V (means 75%VCC)

if we use this specification then we should have for

Spec for 2.5V is VT+min 0.875V and VT+max 1.875V -> is this correct?

- quiescent current:

For total max. quiescent calculation of the complete chip is this calculation correct?

Iq = Iicc+ 8 x Ii = 2uA + 8x1uA = 10uA?

Many Thanks

Josef

0 Clemens Ladisch over 3 years ago

Guru 258910 points

How to calculate the quiescent current depends on how you define it. If you do want to include the input leakage, then this formula is correct.

0 Michael Daimer over 3 years ago in reply to Clemens Ladisch

Hello Clemens,

I have a follow up question on the topic above:

As an example I have chosen the values for Vcc = 2V and entered them in a diagram.

VT+Min = 0.7V means that worst case at Vin = 0.7V the NAND could count that as logic high level?
Between 0.7V and 1V VT- and VT+ area is overlapping each other.

If VT+ is 0.9V, then VT- is 0.7V maximum, because VHysteresisMin = 0.2V -> Correct?

Is the hysteresis value given to make sure that VT- can never be bigger than VT+?

Thanks and best regards,

Michael

0 Clemens Ladisch over 3 years ago in reply to Michael Daimer

Guru 258910 points

Correct. VT+ is always above VT−, i.e., the hysteresis is always positive (and always larger than 0.2 V).

Logic forum