# How can I find the maximum operating frequency of a general-purpose logic IC?

If the seat of the general-purpose logic IC does not contain a description of the maximum operating frequency, the propagation delay time (tpLH, tpHL) can be roughly estimated using the following formula. Maximum operating frequency ≒ 1/ (tpLH + tpHL)

Table 1 shows the propagation delay times of representative products in each series and the results of the above formula.
Propagation delay times depend on the IC function. For ICs other than the typical ICs shown below, see the datasheet for propagation delay times and use them to calculate the maximum operating frequency. Propagation delay times also depend on wire lengths and loads in actual applications.
The maximum operating frequencies shown below should be considered only as a guide. Be sure to verify that the ICs you have selected operate properly under actual usage conditions.

Table-1 Maximum operating frequency by series of general-purpose logic IC (calculated value)

Type

Series Name

CMOS Logic IC
Series No.

One-Gate Logic ( L-MOS ) Equivalents

Operating Voltage Range
VCC (V)

Output current*2, IOUT (mA)

tpLH ,tpHL( ns )*1
CL = 50pF

Maximum Operating Frequency (Calculated value) (MHz)

For 5-V Systems

Standard

3 to 18

±0.51
(at 5.0 V)

200
(at 5.0 V)

3

High Speed

TC74HC

2 to 6

±4.0 or ±6.0
(at 4.5 V)
(±2.0 in the case of TC7S）

23
(at 4.5 V)

22

TC74HCT

TC7WT

4.5 to 5.5

31
(at 4.5 V)

17

TC74AC

-

2 to 5.5

± 24
(at 4.5 V)

8.5
(at 4.5 V)

59

TC74ACT

4.5 to 5.5

9.0
(at 5.0 V)

56

Very High Speed

2 to 5.5

± 8.0
(at 4.5 V)

8.5
(at 5.0 V)

59

10
(at 5.0 V)

50

TC7SET

9.5
(at 5.0 V)

53

4.5 to 5.5

8.5
(at 5.0 V)

59

For low voltage Systems

Low Voltage

1.8 to 5.5

± 16
(at 4.5 V)

6.5
(at 3.3 V)

77

Very Low Voltage

TC74VCX

7UL

1.65 to 3.6
(1.65 to 5.5 in the case of TC7SZ/PZ/WZ)

± 24
(at 3.0 V)
(±8.0 in the case of 7UL）

4.2
(at 2.3 V)

114

*1: Maximum propagation delay time of typical ICs (TC4001, TC74HC244, TC74HCT244, TC74AC244, TC74ACT244, 74VHC244, 74VHC9541 (An-Yn), VHCT244, VHCV244, 74LCX244, and TC74VCX244) at -40 to 85 °C, except for the TC4001 for which the maximum propagation delay time at 25 °C is shown.
*2: Those output current values are from DC Characteristics table of the datasheet. In addition, absolute maximum ratings also specify the current.