Product Overview
The Fairchild Semiconductor 74AC161SCX is a high-speed synchronous 4-bit binary counter implemented in the advanced CMOS (AC) technology. It belongs to the 74AC family, designed to offer high-speed operation with low power consumption, making it suitable for a wide range of digital applications including frequency division, event counting, and time delay circuits. The device features synchronous counting, meaning that all flip-flops within the counter are triggered simultaneously by the clock edge, which eliminates ripple delays typical of asynchronous counters and improves timing performance.

Functional Description
The 74AC161SCX is a synchronous 4-bit binary counter with asynchronous clear and synchronous load capabilities. It counts from 0 to 15 (4 bits) and then rolls over. The counting operation advances on the rising edge of the clock signal when the enable inputs are appropriately set. It includes asynchronous clear (reset) input, which immediately sets the count to zero regardless of the clock, and synchronous load input that allows the counter to be preset with a desired value on the next clock pulse. This makes the device highly versatile for programmable counting sequences.

Pin Configuration and Description

* Clock (CLK): Rising edge triggered input that controls the counting operation.
* Clear (CLR): Asynchronous active-low input that resets the counter to zero immediately.
* Load (LOAD): Active-low synchronous input used to load data from the input pins into the counter on the rising clock edge.
* Enable Inputs (ENP and ENT): Two enable inputs that must be high for the counter to advance; ENT is used for cascading counters.
* Data Inputs (D0-D3): Four parallel data inputs used for synchronous loading of a preset value into the counter.
* Outputs (Q0-Q3): Four outputs representing the current count value in binary format.
* Ripple Carry Output (RCO): Output that goes high when the counter reaches terminal count and both enable inputs are high, used for cascading multiple counters.

Key Features

* High-speed operation typical of AC family, with propagation delays in the range of a few nanoseconds.
* Synchronous counting reduces timing errors and improves predictability in digital systems.
* Asynchronous clear for immediate reset functionality.
* Synchronous load for presetting counter values.
* Dual enable inputs for flexible control and cascading multiple counters.
* Low power consumption, suitable for battery-powered and portable devices.
* TTL compatible inputs ensure easy interfacing with a wide range of digital logic families.
* Wide supply voltage range (typically 2V to 6V) allows operation in diverse system environments.

Electrical Characteristics

* Supply Voltage (VCC): 2.0 V to 6.0 V, typically 5 V for standard applications.
* Input Voltage Levels: TTL compatible with input high-level voltage minimum around 2.0 V and input low-level voltage maximum around 0.8 V.
* Operating Temperature Range: -40°C to +85°C industrial grade.
* Input Leakage Current: Typically in the nanoampere range, ensuring minimal loading on input signals.
* Output Drive Capability: Can source or sink typical TTL logic current levels, allowing direct driving of standard logic inputs.
* Propagation Delay: Typical clock to output delay of approximately 10 to 15 ns at 5 V supply.
* Maximum Clock Frequency: Can operate reliably up to approximately 90 MHz under typical conditions.
* Power Dissipation: Low quiescent current in the microampere range, with dynamic power consumption depending on switching frequency.

Timing Characteristics

* Setup time for data and enable inputs relative to the clock rising edge typically in the range of 5 to 7 ns.
* Hold times are generally around 0 to 3 ns, ensuring robust operation without timing hazards.
* Asynchronous clear propagation delay is typically under 10 ns, providing fast reset capability.

Typical Applications

* Digital event counters and frequency dividers.
* Programmable dividers or timers in digital systems.
* Cascaded counters for higher bit count applications using RCO output.
* Digital clocks and timers.
* Sequential logic circuits and state machines.
* Pulse generation and timing adjustment circuits.

Package and Physical Dimensions
The 74AC161SCX is typically available in a standard Small Outline Integrated Circuit (SOIC) package, featuring 16 pins with a compact footprint for space-saving PCB designs. The package ensures good thermal dissipation and reliable soldering performance in surface-mount assembly lines.

Summary
Fairchild Semiconductor’s 74AC161SCX is a versatile, high-performance synchronous 4-bit binary counter optimized for fast digital logic systems. Its combination of synchronous operation, asynchronous clear, synchronous parallel load, and dual enables make it an ideal choice for complex counting and timing applications. With fast propagation delays, TTL input compatibility, and low power consumption, it integrates easily into a variety of digital systems requiring precise and reliable counting functions.