The difference between 74HC series chips

74LS is a TTL type integrated circuit, 74HC is a CMOS integrated circuit

The difference between 74HCLS/HCTF series chips:

1. LS is a low-power Schottky, HC is a high-speed COMS. LS is slightly faster than HC. HCT input and output are compatible with LS, but low power consumption: F is a high-speed Schottky circuit

2. LS is TTL level, HC is COMS level

3. The LS input is open to high level, and the HC input is not allowed to be open. He generally requires a pull-up and pull-down resistor to determine the level when the input is invalid. LS does not have this requirement

4. The pull-down of LS output is strong and the pull-up is weak, and the pull-down of HC is the same.

5. The working voltage is different. LS can only use SV, while HC is generally 2V to 6V; while the working voltage of HCT is generally 4.5V-55V.

6. Different levels. LS is TEL level, its low level and high level are respectively 08 and V24, while CMOS is 03V and 3.6V when the working voltage is 5V, so CMOS can drive TTL, but the reverse is not possible

7. The driving capability is different. The high level driving capability of LS is 5mA and the low level is 20mA; while the high and low level of CMOS are both 5mA

8. CMOS devices have poor antistatic ability and are prone to latch-up problems, so the input pins of CMOS cannot be directly connected to power.

74 series integrated circuits can be roughly divided into 6 categories

74××(standard type)

74LSxx (Low Power Schottky)

74Sxx (Schottky)

74ALS×x (Advanced Low Power Schottky)

74ASxx (Advanced Schottky);

74F×× (high speed).

In recent years, 74 series of high-speed CMOS circuits have also appeared. This series can be divided into 3 categories



HC is the working level of COMS;

HCT is TTL working level, which can be used interchangeably with 74LS series

HCU is suitable for CMOS circuits without buffer stage

These 9 74 series products have the same logic function and pin arrangement as long as the labels are the same. Different types of 74 series products can be selected according to different conditions and requirements. For example, if the power supply voltage of the circuit is 3V, 74HC series products should be selected.



Series level typical transmission delay ns Maximum drive current (- Toh/Lol) mA

AHC CMOS 8. 5-8/8

AHCT COMS/TTL 8.5-8/8

HC COMS 25-8/8

HCT COMS/TTL 25-8/8

ACT COMS/TTL 10-24/24

FTTL6.5-15/64

ALS TTL 10-15/64

STTL18-15/24

Note: 74 series, 74HC series and 74LS series chips of the same model have the same logic function.