1. General Information

️· Device Type: 8-bit Shift Registers
️· Manufacturer: Nexperia
️· Datasheet Revision: Rev. 7 - 20 October 2022
️· Operating Voltage: Different voltage ranges for the HC and HCT versions (explained below)

2. 74HC594 – Characteristics

️· Supply Voltage Range: Not explicitly given in these excerpts, but implied to be consistent with other 74HC devices, typically 2V to 6V
️· Input Voltage Range:
- VIH (High-level input voltage): 1.5V (at 25°C, but variable with temperature - see the "Tamb = -40 °C to +125 °C" table)
- VIL (Low-level input voltage): 0.5V
️· Output Voltage Levels:
- VOH (High-level output voltage): around 3.7V to 5.2V (dependent on load current and supply voltage)
- VOL (Low-level output voltage): around 0.4V
️· Input Leakage Current (II): ±1.0 μA (at 6.0 V and 125°C)
️· Supply Current (ICC): 160 μA (at 6.0 V, 125°C and IO = 0 A)
️· Additional Supply Current (ΔICC): This is significant. It refers to the extra current drawn when input pins are actively driven. Values are listed for various input pins. Note the difference in values between the SHR, SHCP, STCP, STR, and DS pins. The STR pin draws the highest extra current.
️· Input Capacitance (Ci): 3.5 pF

3. 74HCT594 – Characteristics

️· Supply Voltage Range: 4.5 V to 5.5 V. This is the *key* difference. HCT versions are designed for TTL-compatible logic levels (5V).
️· Input Voltage Range:
- VIH (High-level input voltage): 2.0V
- VIL (Low-level input voltage): 1.2V
️· Output Voltage Levels:
- VOH (High-level output voltage): around 3.98V to 5.2V (dependent on load current and supply voltage)
- VOL (Low-level output voltage): around 0.15 to 0.4V
️· Input Leakage Current (II): ±0.1 μA (at 5.5 V and 125°C)
️· Supply Current (ICC): 8.0 μA (at 5.5 V, 125°C and IO = 0 A)
️· Additional Supply Current (ΔICC): Also significant. Refers to the extra current drawn when input pins are actively driven. Note differences between the SHCP, STCP, STR, and DS pins.
️· Input Capacitance (Ci): 3.5 pF

4. Key Differences between 74HC594 and 74HCT594

️· Supply Voltage: The most important difference. 74HC is designed for lower voltages (2V-6V) and 74HCT is designed for TTL logic (4.5-5.5V).
️· Input Voltage Levels: The input voltage thresholds (VIH and VIL) are different to suit the respective voltage ranges.
️· Leakage Current: Generally the 74HCT has lower leakage current.
️· Additional Supply Current (ΔICC): The values are lower for the HCT series.
️· TTL Compatibility: The HCT version is TTL-compatible, meaning its output levels are suitable for directly interfacing with standard 5V TTL logic circuits. The HC series is not.

Important Notes:

️· Temperature Dependence: The voltage levels and currents are all affected by temperature. The provided datasheet excerpts give values at 25°C, but this will vary with temperature.
️· Load Conditions: The output voltage levels (VOH and VOL) are heavily dependent on the load current. The stated values are for specific load conditions.
️· Always Refer to the Complete Datasheet: These excerpts provide some key information but it’s essential to consult the full datasheet for detailed specifications, timing diagrams, and application notes.