Onsemi MC14538BDR2G Dual Precision Monostable Multivibrator: Datasheet, Pinout, and Application Circuits
The MC14538BDR2G from onsemi is a highly versatile, dual monostable multivibrator (one-shot) integrated circuit from the venerable 4000-series CMOS logic family. Renowned for its precision and stability, this device is engineered to generate a clean, accurately timed output pulse upon receiving an input trigger. Its ability to function in either retriggerable or non-retriggerable modes makes it an indispensable component for a vast array of timing applications in digital systems.
This IC is housed in a common SOIC-16 package, making it suitable for both prototyping and compact PCB designs. Each of the two independent monostable circuits within the package features complementary outputs (Q and \Q), providing design flexibility.
Key Datasheet Specifications
The MC14538B operates over a wide supply voltage range, typically from 3V to 18V, allowing it to interface with various logic families. Its timing period is primarily determined by external components: a resistor (\(R_X\)) and a capacitor (\(C_X\)). The output pulse width is given by the formula \(t = R_X \times C_X\), offering designers direct control over the timing interval.
Critical electrical characteristics include:
Low Power Consumption: Inherent to CMOS technology, making it ideal for battery-operated devices.
High Noise Immunity: A standard feature of the 4000 series, ensuring reliable operation in electrically noisy environments.
Trigger Options: Each monostable can be triggered by a positive or negative edge on its inputs, providing significant application flexibility.
Pinout Configuration
Understanding the pinout is crucial for circuit design. The SOIC-16 pinout is as follows:
Pins 1, 15: Output Q (Monostable 1, 2)
Pins 2, 14: Output \Q (Monostable 1, 2)
Pins 3, 13: Input Trigger A (Positive-edge trigger for Monostable 1, 2)
Pins 4, 12: Input Trigger B (Negative-edge trigger for Monostable 1, 2)
Pins 5, 11: Reset (Active LOW; resets output when LOW)
Pins 6, 10: External Capacitor (\(C_X\)) connection (Monostable 1, 2)
Pins 7, 9: External Resistor/Capacitor junction (\(R_X/C_X\)) (Monostable 1, 2)
Pin 8: Ground (VSS)
Pin 16: Supply Voltage (VDD)
Application Circuits
The MC14538B's versatility is best demonstrated through its application circuits.
1. Basic Non-Retriggerable One-Shot: This is the simplest mode. The timing components \(R_X\) and \(C_X\) are connected between their designated pins (e.g., Pin 9 and Pin 16 for VDD, and Pin 10 and Pin 8 for GND). A trigger pulse applied to either the A or B input (with the other held at the appropriate logic level) initiates a single output pulse of a precise duration, regardless of subsequent trigger events during this period.
2. Retriggerable Pulse Extender: In this configuration, the output pulse width can be extended by applying a new trigger pulse before the current timing period expires. This is exceptionally useful for debouncing mechanical switches or for creating a "watchdog" timer that remains active as long as a periodic signal is present.
3. Cascaded Timers for Long Delays: For generating very long delays that would require impractically large resistors or capacitors with a single timer, multiple monostables can be cascaded. The output of the first timer triggers the second, effectively multiplying the individual time periods (\(t_{total} = t1 \times t2\)).
The onsemi MC14538BDR2G stands as a proven and reliable solution for precision timing tasks. Its dual independent channels, flexible triggering and reset options, and wide operating voltage range make it a superior choice over basic 555 timers in many complex digital systems. Whether used for pulse shaping, debouncing, sequential timing, or creating time delays, this IC offers a robust and predictable performance that modern designers continue to leverage.
Keywords:
Monostable Multivibrator, Pulse Width Timing, Retriggerable, CMOS Logic, Application Circuits
