Dual Monostable Multivibrators
This multivibrator features a negative-transition-triggered input and a positive-transition-triggered input either of which
can be used as an inhibit input. Pulse triggering occurs at a particular voltage level and is not directly related to the
transition time of the input pulse. Schmitt-trigger input circuitry (TTL hysteresis) for B input allows jitter-free
triggering from inputs with transition rates as slow as 1 V/s, providing the circuit with excellent noise immunity of
typically 1.2 V. A high immunity to VCC noise of typically 1.5 V is also provided by internal latching circuitry. Once
fired, the outputs are independent of further transitions of the A and B inputs and are a function of the timing
components, or the output pulses can be terminated by the overriding clear. Input pulses may be of any duration
relative to the output pulse. Output rise and fall times are TTL compatible and independent of pulse length.
Typical triggering and clearing sequence are illustrated as a part of the switching characteristics waveforms. Pulse
width stability is achieved through internal compensation and is virtually independent of VCC and temperature.
In most applications, pulse stability will only be limited by the accuracy of external timing components. Jitter-free
operation is maintained over the full temperature and VCC range for more than six decades of timing capacitance (10 pF
to 10 µF) and more than one decade of timing resistance (2 kΩ to 100 kΩ).
Throughout these ranges, pulse width is defined by the relationship: tw (out) = Cext • Rext • 1n 2.
• Ordering Information
HD74LS221RPEL SOP-16 pin (JEDEC)
Note: Please consult the sales office for the above package availability.
EL (2,500 pcs/reel)
Rev.3.00, Jul.15.2005, page 1 of 8