📌 Product Overview
The SN54HC164 / SN74HC164 is an 8-bit parallel-out serial shift register designed for data conversion and expansion in logic-level systems. 💡 Targeting Programmable Logic Controllers (PLCs), industrial automation, and LED display matrices, this device converts serial data streams into parallel outputs. Engineers typically select this component for I/O expansion or display driving where board space is limited, utilizing its wide operating voltage range (2V to 6V) to bridge logic families. Critical selection variables include clock frequency (up to 20ns propagation delay) and output drive current (±4mA) to ensure signal integrity under load.
🎯 Typical Applications & Design Context
This component excels in environments requiring efficient data routing without heavy MCU overhead. 👇 Key scenarios include:
- Industrial PLCs: Utilized to expand limited I/O lines across multiple control relays or sensors, leveraging the HC family's robust noise immunity.
- Video Display Systems: Ideal for driving segmented LED or LCD displays where the serial-to-parallel conversion reduces necessary wiring traces.
- Appliance Control: Used in front-panel interfaces for status indicators and mode switching.
The device suits these applications due to its low power consumption (80-μA max Icc) and AND-gated serial inputs, which allow for sophisticated data control lines that can inhibit or enable data flow without complex external gating.
📊 Key Technical Specifications
- Supply Voltage Range: 2 V to 6 V
- Output Drive Current: ±4 mA at 5 V VCC
- Operating Temperature (Commercial): –40°C to 85°C (SN74HC Series)
- Operating Temperature (Military): –55°C to 125°C (SN54HC Series)
- Propagation Delay (t_pd): Typical 20 ns
- Input Current: 1 μA Maximum
| Parameter | Value | Notes |
|---|---|---|
| Supply Voltage (VCC) | 2 V – 6 V | Wide operating range for mixed-voltage systems |
| Clock Frequency (f_max) | Determined by t_pd | Typically supports high-speed logic up to several MHz |
| Output Drive | ±4 mA @ 5V | Can drive up to 10 LSTTL loads |
| Power Dissipation | Low static power | 80-μA max Icc |
⚠️ Absolute Maximum Ratings & Process Limits
Exceeding these parameters risks permanent silicon damage or latent reliability failures in the field. 🚨
- Supply Voltage: –0.5 V to 7 V (Exceeding 7V causes immediate gate oxide breakdown).
- Input Current: ±20 mA (Clamping diodes may fail if this is exceeded, leading to open circuits).
- Continuous Output Current: ±25 mA (Exceeding this leads to bond wire fusing or metallization melt).
- Storage Temperature: –65°C to 150°C.
E-E-A-T Insight:
While the datasheet lists a max output current of ±25mA, designs relying on this limit for sustained periods (e.g., directly driving LEDs without limiting resistors) often experience thermal runaway. Furthermore, for the PRF-38535 compliant versions (SN54HC164), all parameters are 100% tested in production, whereas commercial versions may rely on sampling. In mass production SMT, exceeding the maximum junction temperature during reflow can degrade the AND-gated input characteristics, causing unexpected data latching failures later in the product lifecycle.
🧩 Package, Dimensions & Assembly Notes
This device is available in various through-hole and surface-mount packages. 👇
- PDIP (14): 19.30mm × 6.35mm (Legacy/Prototyping)
- SOIC (14): 8.65mm × 3.91mm (Standard SMT)
- TSSOP (14): 5.00mm × 4.40mm (High-density layouts)
- LCCC (14): 9.39mm × 9.39mm (Military/Harsh Environment)
Assembly Note:
For the SN54HC164 in ceramic packages (CFP/LCCC), moisture sensitivity is less of a concern than plastic packages, but CTE mismatch must be managed on the PCB to prevent pad lifting during thermal cycling. Ensure the Clock (CLK) and Clear (CLR) traces are impedance-controlled and kept short to prevent ringing, as the HC family inputs are sensitive to fast edge rates coupled with long inductive traces.
🔍 Procurement & Sourcing Insights
Sourcing Logic ICs like the SNx4HC164 requires attention to temperature grade and origin of manufacture.
- Supply Chain Stability: This is a mature, long-lifecycle product, but "54" series (Military) parts often have significantly longer lead times than "74" series (Commercial).
- Counterfeit Risk: High in the open market. Authentic MIL-PRF-38535 parts require specific traceability certs.
- Alternative Validation: When swapping brands (e.g., TI to Nexperia or ON Semi), verify the Reset (CLR) pin timing. Some alternatives have different propagation delays on the clear function, which can cause glitches in high-speed PLCs.
- Binning: No speed binning is typically required, but power consumption varies by manufacturer.
❓ FAQ
Q: Can I use the SN74HC164 to directly drive LEDs?
A: Yes, but strictly with current limiting. While it can source/sink ±4mA, driving an LED at 20mA continuously requires a driver transistor. Exceeding ±4mA nominal will degrade the output voltage swing (V_OL/V_OH) and eventually damage the IC.
Q: What is the difference between SN54HC164 and SN74HC164?
A: The SN54 series is built to MIL-PRF-38535 standards, tested for –55°C to 125°C operation, and often housed in hermetic ceramic packages. The SN74 series is for commercial use (0°C to 70°C or –40°C to 85°C) in plastic packages. Using the commercial grade in an industrial setting above 85°C risks data corruption.
Q: Do I need a pull-up resistor on the Serial Inputs (A & B)?
A: Not strictly required if driven actively. However, if the input lines are long or subject to electromagnetic noise (common in industrial cabinets), unused inputs should be tied to ground or VCC, and active lines may benefit from series termination to prevent false clocking.
Q: How do I validate an alternative brand for this shift register?
A: Check the Input Capacitance and Output Rise/Fall times. A generic alternative with slower edge rates might work for a slow display but will fail in a high-speed PLC communication loop. Always validate the Setup Time (t_su) relative to your MCU's clock speed.
