74LS221 DIP Dual Monostable Multivibrator with Schmitt-Trigger Inputs
The 74LS221 is a high-speed TTL integrated circuit containing two independent monostable multivibrators (one-shots) designed to provide a highly stable output pulse. This IC is used to generate precise time delays or timed pulses in digital systems. Unlike the 74LS123, the 74LS221 is not retriggerable, meaning that once the timing cycle begins, the output pulse will remain at its programmed width regardless of any subsequent input transitions until the cycle is complete.
This device features Schmitt-trigger architecture on the B-inputs, allowing it to trigger reliably even from slow-rising or noisy input signals. The output pulse width is determined by an external resistor and capacitor ($R_{ext}$ and $C_{ext}$), providing a wide range of timing possibilities from nanoseconds to seconds. It also includes an asynchronous clear input that can immediately terminate the output pulse at any time, ensuring total control over the timing window.
KEY FEATURES
- Dual independent monostable multivibrators in one package
- Non-retriggerable operation for consistent pulse width timing
- Schmitt-trigger inputs for superior noise immunity and slow-signal handling
- Precise pulse width control via external RC components
- Asynchronous clear input to override and end the timing cycle
- Standard 16 pin dual in line package
SPECIFICATIONS
- Supply Voltage 4.75V to 5.25V
- Operating Temperature 0 to 70 Celsius
- Logic Type TTL Low Power Schottky
- Minimum Output Pulse Width 35ns
- Typical Propagation Delay 25ns
- High Level Output Current -0.4mA
- Low Level Output Current 8mA
- Input Voltage High 2.0V Minimum
INTERFACES
- 1A 2A Trigger inputs active low
- 1B 2B Trigger inputs active high (Schmitt-trigger)
- 1CLR 2CLR Clear inputs active low
- 1Q 2Q True pulse outputs
- 1Q BAR 2Q BAR Complementary pulse outputs
- 1Cext 2Cext External capacitor connections
- 1Rext/Cext 2Rext/Cext External resistor/capacitor nodes
- VCC Positive supply voltage
- GND Ground reference
