1. General description

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: tW = 0.7  CEXT  REXT 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 VCC and temperature. In most applications pulse stability

will only be limited by the accuracy of the external timing components. Inputs include

clamp diodes. This enables the use of current limiting resistors to interface inputs to

voltages in excess of VCC.

2. Features and benefits

 Input levels:

 For 74HCT221: TTL level

 Pulse width variance is typically less than 5

 Direct reset terminates output pulse

 Schmitt-trigger action on nB inputs

 ESD protection:

 HBM JESD22-A114F exceeds 2000 V

 MM JESD22-A115-A exceeds 200 V

 Specified from 40 C to +85 C and from 40 C to +125 C