特性 Features

? Overriding RESET Terminates Output Pulse

? Triggering from the Leading or Trailing Edge

? Q and Q Buffered Outputs

? Separate Resets

? Wide Range of Output-Pulse Widths

? Schmitt Trigger on B Inputs

? Fanout (Over Temperature Range)

- Standard Outputs . . . . . . . . . . . . . . . 10 LSTTL Loads

- Bus Driver Outputs . . . . . . . . . . . . . 15 LSTTL Loads

? Wide Operating Temperature Range . . . -55oC to 125oC

? Balanced Propagation Delay and Transition Times

? Significant Power Reduction Compared to LSTTL

Logic ICs

? HC Types

- 2V to 6V Operation

- High Noise Immunity: NIL = 30%, NIH = 30% of VCC

at VCC = 5V

? HCT Types

- 4.5V to 5.5V Operation

- Direct LSTTL Input Logic Compatibility,

VIL= 0.8V (Max), VIH = 2V (Min)

- CMOS Input Compatibility, Il ≤ 1μA at VOL, VOH

描述 Description

The ’HC221 and CD74HCT221 are dual monostable

multivibrators with reset. An external resistor (RX) and an

external capacitor (CX) control the timing and the accuracy

for the circuit. Adjustment of RX and CX provides a wide

range of output pulse widths from the Q and Q terminals.

Pulse triggering on the B input occurs at a particular voltage

level and is not related to the rise and fall time of the trigger

pulse.

Once triggered, the outputs are independent of further trigger

inputs on A and B. The output pulse can be terminated by a

LOW level on the Reset (R) pin. Trailing Edge triggering (A)

and leading-edge-triggering (B) inputs are provided for

triggering from either edge of the input pulse. On power up,

the IC is reset. If either Mono is not used each input (on the

unused device) must be terminated either high or low.

The minimum value of external resistance, RX, is typically 500Ω.

The minimum value of external capacitance, CX, is 0pF. The

calculation for the pulse width is tW = 0.7 RXCX at VCC = 4.5V.