74LV123

The 74LV123 is a low-voltage Si-gate CMOS device and is pin and function compatible with the 74HC/HCT123.

The 74LV123 is a dual retriggerable monostable multivibrator with output pulse width control by three methods. The basic pulse time is programmed by selection of an external resistor (R_EXT) and capacitor (C_EXT). They are normally connected as shown in Figure 1. Once triggered, the basic output pulse width may be extended by retriggering the gated active LOW-going edge input (nA) or the active HIGH-going edge input (nB). By repeating this process, the output pulse period (nQ = HIGH, nQ = LOW) of the 74LV123 can be made as long as desired. Alternatively, an output delay can be terminated at any time by a LOW-going edge on input nR_D, which also inhibits the triggering. Figures 1 and 2 illustrate pulse control by retriggering and early reset. The basic output pulse width is essentially determined by the values of the external timing components R_EXT and C_EXT. For pulse width when C_EXT <10000pF,see Figure 5. When C_{EXT  >} 10,000pF, the typical output pulse width is defined as: t_W = 0.45x R_EXT x C_EXT (typ.), where tW = pulse width in ns; REXT = external resistor in KW; and C_EXT = external capacitor in pF. Schmitt-trigger action in the nA and nB inputs makes the circuit highly tolerant of slower input rise and fall times.