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M74HC123 Dataheets PDF



Part Number M74HC123
Manufacturers ST Microelectronics
Logo ST Microelectronics
Description DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR
Datasheet M74HC123 DatasheetM74HC123 Datasheet (PDF)

M54HC123/123A M74HC123/123A DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR . . . . . . . . . HIGH SPEED tPD = 25 ns (TYP) at VCC = 5V LOW POWER DISSIPATION STANDBY STATE ICC=4 µA (MAX.) AT TA=25°C ACTIVE STATE ICC = 200 µA (TYP.) AT VCC=5V HIGH NOISE IMMUNITY VNIH = VNIL = 28 % VCC (MIN.) OUTPUT DRIVE CAPABILITY 10 LSTTL LOADS SYMMETRICAL OUTPUT IMPEDANCE IOH = IOL = 4 mA (MIN.) BALANCED PROPAGATION DELAYS tPLH = tPHL WIDE OPERATING VOLTAGE RANGE VCC (OPR) = 2 V TO 6 V WIDE OUTPUT PULSE WIDTH RAN.

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M54HC123/123A M74HC123/123A DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR . . . . . . . . . HIGH SPEED tPD = 25 ns (TYP) at VCC = 5V LOW POWER DISSIPATION STANDBY STATE ICC=4 µA (MAX.) AT TA=25°C ACTIVE STATE ICC = 200 µA (TYP.) AT VCC=5V HIGH NOISE IMMUNITY VNIH = VNIL = 28 % VCC (MIN.) OUTPUT DRIVE CAPABILITY 10 LSTTL LOADS SYMMETRICAL OUTPUT IMPEDANCE IOH = IOL = 4 mA (MIN.) BALANCED PROPAGATION DELAYS tPLH = tPHL WIDE OPERATING VOLTAGE RANGE VCC (OPR) = 2 V TO 6 V WIDE OUTPUT PULSE WIDTH RANGE tWOUT = 120 ns ∼ 60 s OVER AT VCC = 4.5 V PIN AND FUNCTION COMPATIBLE WITH 54/74LS123 B1R (Plastic Package) F1R (Ceramic Package) M1R (Micro Package) C1R (Chip Carrier) ORDER CODES : M54HCXXXF1R M74HCXXXM1R M74HCXXXB1R M74HCXXXC1R DESCRIPTION The M54/74HC123 is a high speed CMOS MONOSTABLE multivibrator fabricated with silicon gate C2MOS technology. It achieves the high speed operation similar to equivalent LSTTL while maintaining the CMOS low power dissipation. There are two trigger inputs, A INPUT (negative edge) and 8 INPUT (positive edge). These inputs are valid for slow rising/falling signals, (tr = tf = I sec). The device may also be triggered by using the CLR input (positive-edge) because of the Schmitt-trigger input ; after triggering the output maintains the MONOSTABLE state for the time period determined by the external resistor Rx and capacitor Cx. When Cx ≥ 10nF and Rx ≥ 10KΩ, the output pulse width value is approssimatively given by the formula: tw(out) = K • Cx • Rx. Two different pulse width constant are available: K ≅ 0.45 for HC123 K ≅ 1 for HC123A. Taking CLR low breaks this MONOSTABLE STATE. If the next trigger pulse occurs during the MONOSTABLEperiod it makes the MONOSTABLE period longer. Limit for values of Cx and Rx : Cx : NO LIMIT Rx : VCC < 3.0 V 5 K Ω to 1 M Ω VCC ≥ 3.0 V 1 K Ω to 1 M Ω All inputs are equipped with protection circuits PIN CONNECTIONS (top view) NC = No Internal Connection October 1993 1/14 M54/M74HC123/123A SYSTEM DIAGRAM TIMING CHART 2/14 M54/M74HC123/123A BLOCK DIAGRAM Note : (1) Cx, Rx, Dx are external components. (2) Dx is a clamping diode. The external capacitor is charged to VCC inthe stand-by state, i.e. no trigger. When the supply voltage is turned off Cx is discharged mainly through an internal parasitic diode (see figures). If Cx is sufficiently large and VCC decreases rapidy, there will be some possibility of damaging the I.C. with a surge current or latch-up. If the voltage supply filter capacitor is large enough and VCC decrease slowly, the surge current is automatically limited and damage the I.C. is avoided. The maximum forward current of the parasitic diode is approximately 20 mA. In cases where Cx is large the time taken for the supply voltage to fall to 0.4 VCC can be calculated as follows : tf ≥ (VCC – 0.7) ⋅ Cx/20mA In cases where tf is too short an external clamping diode is required to protect the I.C. from the surge current. FUNCTIONAL DESCRIPTION STAND-BY STATE The external capacitor, Cx, is fully charged to VCC in the stand-by state. Hence, before triggering, transistor Qp and Qn (connected to the Rx/Cx node) are both turned-off. The two comparators that control the timing and the two reference voltage sources stop operating. The total supply current is therefore only leakage current. TRIGGER OPERATION Triggering occurs when : 1 st) A is ”low” and B has a falling edge ; 2 nd) B is ”high” and A has a rising edge ; 3 rd) A is low and B is high and C1 has a rising edge. After the multivibrator has been retriggered comparator C1 and C2 start operating and Qn is turned on. Cx then discharges through Qn. The voltage at the node R/C external falls. When it reaches VREFL the output of comparator C1 becomes low. This in turn resets the flip-flop and Qn is turned off. At this point C1 stops functioning but C2 continues to operate. The voltage at R/C external begins to rise with a time constant set by the external components Rx, Cx. Triggering the multivibrator causes Q to go high after internal delay due to the flip-flop and the gate. Q remains high until the voltage at R/C external rises again to VREFH. At this point C2 output goes low and O goes low. C2 stop operating. That means that after triggering when the voltage R/C external returns to VREFH the multivibrator has returned to its MONOSTABLE STATE. In the case where Rx ⋅ Cx are large enough and the discharge time of the capacitor and the delay time in the I.C. can be ignored, the width of the output pulse tw (out) is as follows : tW(OUT) = 0.46 Cx ⋅ Rx (HC123) tW(OUT) = Cx ⋅ Rx (HC123A) 3/14 M54/M74HC123/123A FUNCTIONAL DESCRIPTION (continued) RE-TRIGGERED OPERATION When a second trigger pulse follows the first its effect will depend on the state of the multivibrator. If the capacitor Cx is being charged the voltage level of R/C external falls to Vrefl again and Q remains high i.e. the retrigger pulse arrives in a time shorter than the period Rx ⋅ Cx seconds, the capacitor charging t.


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