74HCT221

The 74HCT221 is a dual non-retriggerable monostable multivibrator. Each multivibrator features edge-triggered inputs (nA and nB), either of which can be used as an enable 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 for the nB inputs allow jitter-free triggering from inputs with slow transition rates, providing the circuit with excellent noise immunity. Once triggered, the outputs (nQ, nQ) are independent of further transitions of nA and nB inputs. The output pulse width is defined by the following relationship:

• t_W = 0.7 × C_EXTR_EXT

The output pulses can be terminated by the active LOW reset inputs (nRD). Pulse width stability is achieved through internal compensation and is virtually independent of V_CC and temperature. In most applications pulse stability will only be limited by the accuracy of the external timing components . This device features reduced input threshold levels to allow interfacing to TTL logic levels. Inputs also include clamp diodes, this enables the use of current limiting resistors to interface inputs to voltages in excess of V_CC.