Tell me about the input tolerant function.

The input/output-equivalent circuit and the allowable input/output voltage specifications are shown below:

The input-tolerant function is designed to prevent current from flowing from an input to the power supply when the input voltage is set higher than the power supply voltage or when power supply (Vcc) = 0 V.

The allowable input voltage specification is shown in the Input Voltage section of the Recommended Operating Conditions table. When the input/output voltage range is 0 - Vcc, voltage in excess of Vcc must not be applied because the circuit has a diode.

The input voltage range of VHC/LCX is 0 - 5.5 V (with the input-tolerant function); thus, up to 5.5 V can be applied to the input regardless of the power supply voltage. When the power supply voltage (Vcc) = 3.3 V, VHC/LCX provides voltage conversion from 5 V to 3.3 V.

The input voltage range of VHC/LCX is 0 - 3.6V (with the input-tolerant function); thus, up to 3.6V can be applied to the input regardless of the power supply voltage. When the power supply voltage (Vcc) = 1.8V, VHC/LCX provides voltage conversion from 3.3 V to 1.8 V.

Input/output equivalent circuit and specifications of allowable input/output voltages
tolerant function Both input/output input only Neither input/output
series VHCT,LCX,VCX VHC AC/ACT,HC/HCT
input/output equivalent circuit
allowable input voltage operating 0 - 5.5V (VCX 3.6V) 0 - 5.5V (VCX 3.6V) 0 - VCC
Power down 0 - 5.5V (VCX 3.6V) 0 - 5.5V (VCX 3.6V) 0V (voltage cannot be supplied)
allowable output voltage output enable 0 - VCC 0 - VCC 0 - VCC
output disable 0 - 5.5V (VCX 3.6V) 0 - VCC 0 - VCC
Power down 0 - 5.5V (VCX 3.6V) 0V (voltage cannot be supplied) 0V (voltage cannot be supplied)
Recommended Operating Conditions in the Data Sheet
Item Symbol
(Unit)
Rating Remarks
TC74VHC TC74LCX TC74VCX
Power supply voltage VCC
(V)
2 - 5.5 2 - 3.6 1.65 - 3.6  
Input voltage VIN
(V)
0 - 5.5 0 - 5.5 0 - 3.6 With input tolerant function
Output voltage VOUT
(V)
0 - VCC 0 - 5.5
(Note 1)
0 - 3.6
(Note 1)
LCX and VCX: with output tolerant function
0 - VCCA
(Note 2)
0 - VCCA
(Note 2)
  • Note 1: output HZ
  • Note 2: output "H" or "L"

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