74VHC221A

The 74VHC221A is an advanced high speed CMOS Monostable Multivibrator fabricated with silicon gate CMOS technology. It achieves the high speed operation similar to equivalent Bipolar Schottky TTL while maintaining the CMOS low power dissipation. Each multivibrator features both a negative, A, and a positive, B, transition triggered input, either of which can be used as an inhibit input. Also included is a clear input that when taken LOW resets the one-shot. The VHC221A can be triggered on the positive transition of the clear while A is held LOW and B is held HIGH. The VHC221A is non-retriggerable, and therefore cannot be retriggered until the output pulse times out. The output pulse width is determined by the equation:
     PW = (Rx)(Cx); where PW is in seconds, R is in ohms,and C is in farads.
     Limits for Rx and Cx are:
          External capacitor, Cx: No limit
          External resistors, Rx: V_CC= 2.0V, 5 k min
                                              V_CC > 3.0V, 1 k min
An input protection circuit of the 74VHC221A  ensures that 0 to 7V can be applied to the input pins without regard to the supply voltage.This device can be used to interface 5V to 3V systems and two supply systems such as battery back up. This circuit prevents device destruction due to mismatched supply and input voltages.