74LS221 Dual Monostable Multivibrator IC with Schmitt-Trigger Inputs

The 74LS221 designed as a monolithic dual multivibrator with performance characteristics virtually identical to those of the 74LS121 devices. Each multivibrator in the IC features a negative transition triggered input and a positive transition triggered input, either of which used as an inhibit input. The 74LS221 IC has a wide range of working voltage, a wide range of working conditions, and directly interfaces with CMOS, NMOS, and TTL configurations. Moreover, the output of the IC always comes in TTL.  Thus makes it easy to work with other TTL devices and microcontrollers.

Pulse triggering happens at a certain voltage level and is unrelated to the input pulse’s transition time. Schmitt-trigger input circuitry (TTL hysteresis) for B input permits jitter-free triggering from inputs as slow as 1 V/s, offering good noise immunity (usually 1.2 V). Internal latching circuitry also provides a high level of tolerance to VCC noise, generally 1.5 V. Internal compensation achieves pulse-width stability that is almost independent of VCC and temperature. The precision of external timing components is the sole thing that limits pulse stability in most applications.

A monostable multivibrator (MMV), also referred as a one-shot multivibrator. This is pulse generator circuit in which the duration of the pulse is determined by the R-C network, connected externally to the 555 timers. In such a vibrator, one state of output remains stable while the other is in quasi-stable (unstable). For auto-triggering of output from a quasi-stable state to a stable state, energy stored by an externally connected capaci­tor to a reference level. The time taken in storage determines the pulse width.

Applications

• It is generally used in devices such as delay timers & gated circuits, etc.