What does the “H” in the level shifter IC part number “74AVCH” signify?

The “H” in model number “74AVCH” indicates that it is equipped with a bus hold circuit.

The bus hold circuit maintains the input logic state even when the input terminal becomes open (floating) due to a circuit added to the input terminal.

Fig.1　Bus Hold Circuit Example
Fig.1　Bus Hold Circuit Example

Bus Hold Circuit (Fig.1)
The bus hold circuit maintains the logic state using a small-current buffer circuit built into the input section. Therefore, the bus hold circuit defines two current values: the hold current, which is the current required to maintain the input logic, and the overdrive current, which is the current required to change the input logic. To invert the input, the input must have a current capability equal to or greater than the overdrive current. (Table 1)

Table -1 Bus Hold Circuit Hold Current and Overdrive Current (74AVCH2T45)
Characteristics Symbol Test Condition VCCA(V) VCCB(V) Min Typ. Max Unit
Input leakage current IIN VIN(DIR)=0V to 3.6V 0.8 to 3.6 0 to 3.6 - - - μA
High-level input voltage Il(HOLD) VI=0.24V 0.8 0.8 3 - - μA
VI=0.56V 0.8 0.8 -3 - -
VI=0.26V 0.85 0.85 4 - -
VI=0.6V 0.85 0.85 -4 - -
VI=0.29V 0.95 0.95 6 - -
VI=0.67V 0.95 0.95 -6 - -
VI=0.33V 1.1 1.1 10 - -
VI=0.77V 1.1 1.1 -10 - -
VI=0.42V 1.4 1.4 15 - -
VI=0.98V 1.4 1.4 -15 - -
VI=0.50V 1.65 1.65 25 - -
VI=1.15V 1.65 1.65 -25 - -
VI=0.7V 2.3 2.3 45 - -
VI=1.6V 2.3 2.3 -45 - -
VI=0.8V 3.0 3.0 100 - -
VI=2.0V 3.0 3.0 -100 - -
Low-level input voltage II(OD) VI= L →　H 0.8 0.8 50 - - μA
VI= H → L 0.8 0.8 -50 - -
VI= L →　H 0.95 0.95 65 - -
VI= H → L 0.95 0.95 -65 - -
VI= L →　H 1.05 1.05 80 - -
VI= H → L 1.05 1.05 -80 - -
VI= L →　H 1.3 1.3 110 - -
VI= H → L 1.3 1.3 -110 - -
VI= L →　H 1.6 1.6 150 - -
VI= H → L 1.6 1.6 -150 - -
VI= L →　H 1.95 1.95 250 - -
VI= H → L 1.95 1.95 -250 - -
VI= L →　H 2.7 2.7 400 - -
VI= H → L 2.7 2.7 -400 - -
VI= L →　H 3.6 3.6 600 - -
VI= H → L 3.6 3.6 -600 - -

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