SN74LS423 Dual Retriggerable Monostable Multivibrators |

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Dual Retriggerable Monostable Multivibrators

Dual Retriggerable Monostable Multivibrators - SN74LS423


The 'LS422 and 'LS423 are identical to 'LS122 and 'LS123 except they cannot be triggered via clear.

These d-c triggered multivibrators feature output-pulse-width control by three methods. The basic pulse time is programmed by selection of external resistance and capacitance values (see typical application data). The 'LS422 contains an internal timing resistor that allows the circuits to be used with only an external capacitor, if so desired. Once triggered, the basic pulse width may be extended by retriggering the gated low-level-active (A) or high-level-active (B) inputs, or be reduced by use of the overriding clear. Figure 1 illustrates pulse control by retriggering and early clear.

The 'LS422 and 'LS423 have enough Schmitt hysteresis to ensure jitter-free triggering from the B input with transition rates as slow as 0.1 millivolt per nanosecond. The 'LS422 Rint is nominally 10 k ohms.

The SN54LS422 and SN54LS423 are characterized for operation over the full military temperature range of -55°C to 125°C. The SN74LS422 and SN74LS423 are characterized for operation from 0°C to 70°C.FIGURE 1-TYPICAL INPUT/OUTPUT PULSES



  • Will Not Trigger from Clear
  • D-C Triggered from Active-High or Active-Low Gated Logic Inputs
  • Retriggerable for Very Long Output Pulses, Up to 100% Duty Cycle
  • Overriding Clear Terminates Output Pulse
  • 'LS422 Has Internal Timing Resistor

An external timing capacitor may be connected between Cext and Rext/Cext (positive).

To use the internal timing resistor of 'LS422, connect Rint to VCC.

For improved pulse width accuracy and repeatability, connect an external resistor between Rext/Cext and VCC with Rint open-circuited.

To obtain variable pulse widths, connect an external variable resistance between Rint or Rext/Cext and VCC.



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Part number Order Technology Family Input type Output type VCC (Min) (V) VCC (Max) (V) IOL (Max) (mA) IOH (Max) (mA) Rating
SN74LS423 Order now LS     TTL     TTL     4.75     5.25     8     -0.4     Catalog