onsemi MC14538BDR2 Dual Precision Monostable Multivibrator: Datasheet, Application Circuit, and Pinout Configuration
The onsemi MC14538BDR2 is a highly versatile and reliable integrated circuit belonging to the CMOS 4000 series. It functions as a dual, retriggerable, and resettable monostable multivibrator (one-shot), providing two independent timing channels in a single 16-pin package. This device is engineered to generate precise, stable output pulses with a duration determined by external resistors (RT) and capacitors (CT). Its precision and flexibility make it a cornerstone component in a vast array of digital systems for timing, pulse shaping, and sequencing applications.
Pinout Configuration
Understanding the pinout is crucial for effective circuit design. The MC14538BDR2 is housed in a standard SOIC-16 package.
Channel 1 Pins: The first monostable circuit uses pins 1 through 8.
Pin 1 (CT1): Connection for the external timing capacitor.
Pin 2 (RT1/CT1): Connection for the external timing resistor and capacitor.
Pin 3 (RT1): Connection for the external timing resistor.
Pin 4 (A1): One of two trigger inputs (negative-edge trigger).
Pin 5 (B1): The second trigger input (positive-edge trigger).
Pin 6 (CD1): Clear/Direct Reset input (active LOW).
Pin 7 (Q1): True output.
Pin 8 (Q1̅): Complementary output.
Channel 2 Pins: The second, identical monostable circuit uses pins 9 through 16.
Pins 9 (Q2̅), 10 (Q2), 11 (CD2), 12 (B2), 13 (A2), 14 (RT2), 15 (RT2/CT2), 16 (CT2).
Power Supply: VDD (Pin 16) and VSS (Pin 8) provide the positive and ground connections for the entire IC, typically operating from 3V to 18V.
Key Datasheet Specifications
The MC14538B's datasheet outlines its robust electrical characteristics:
Wide Operating Voltage Range: 3.0 V to 18.0 V allows compatibility with TTL and higher-voltage CMOS logic levels.
High Noise Immunity: Standard for CMOS technology, typically 45% of the supply voltage.
Low Power Consumption: A very low quiescent current, making it suitable for battery-powered devices.
Retriggerable and Resettable Functionality: The output pulse width can be extended by applying a new trigger pulse during the active state (retriggerable). The timing cycle can be terminated prematurely by applying a LOW signal to the Clear (CD) pin (resettable).
Trigger Options: The device offers both positive-edge (B input) and negative-edge (A input) triggering, providing immense flexibility in responding to different digital signals.
Application Circuit
A fundamental application circuit for one channel of the MC14538B is a fixed-duration pulse generator. The output pulse width (tW) is approximately given by the formula tW = RT CT.
1. Component Connection: Connect an external resistor (RT) between Pin 3 (RT) and VDD. Connect an external capacitor (CT) between Pin 1 (CT) and VSS. Pin 2 (RT/CT) is joined to the junction of RT and CT.
2. Triggering: A common configuration is to use the B input (positive-edge trigger). The trigger signal is applied to Pin 5 (B1), while Pin 4 (A1) is tied to VDD (logic HIGH).
3. Reset: To ensure normal operation, the Clear input (Pin 6, CD1) is tied to VDD (inactive).
4. Output: Upon receiving a positive-edge trigger signal, the output Q (Pin 7) will go HIGH for the precise duration set by RT and CT, regardless of the length of the input trigger pulse.
This circuit is fundamental in applications such as debouncing mechanical switches, creating time delays between system events, and converting short glitches into well-defined, clean pulses.
The onsemi MC14538BDR2 stands out as a precision workhorse for timing applications. Its dual, independent channels, combined with wide voltage range, retriggerable/resettable features, and flexible triggering options, make it an exceptionally useful and enduring component for digital designers. Its ability to generate accurate pulses from external passive components ensures its continued relevance in both modern and legacy electronic systems.
Keywords
1. Monostable Multivibrator
2. Retriggerable
3. Pulse Width Timing
4. CMOS Logic IC
5. Precision One-Shot
