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DM74LS123 Datasheet(PDF) 3 Page - National Semiconductor (TI) |
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DM74LS123 Datasheet(HTML) 3 Page - National Semiconductor (TI) |
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3 / 6 page 
Switching Characteristics at VCC e 5V and TA e 25 C RL e 2kX Symbol Parameters From (Input) CL e 15pF CL e 15pF Units To (Output) CEXT e 0 pF REXT e 5kX CEXT e 1000 pF REXT e 10 KX Min Max Min Max tPLH Propagation Delay Time AtoQ 33 ns Low to High Level Output tPLH Propagation Delay Time BtoQ 44 ns Low to High Level Output tPHL Propagation Delay Time AtoQ 45 ns High to Low Level Output tPHL Propagation Delay Time BtoQ 56 ns High to Low Level Output tPLH Propagation Delay Time Clear to Q 45 ns Low to High Level Output tPHL Propagation Delay Time Clear to Q 27 ns High to Low Level Output tWQ(Min) Minimum Width of Pulse AorBtoQ 200 ns at Output Q tW(out) Output Pulse Width A or B to Q 4 5 m s Operating Rules 1 An external resistor (RX) and an external capacitor (CX) are required for proper operation The value of CX may vary from 0 to any necessary value For small time con- stants high-grade mica glass polypropylene polycarbon- ate or polystyrene material capacitors may be used For large time constants use tantalum or special aluminum capacitors If the timing capacitors have leakages ap- proaching 100 nA or if stray capacitance from either ter- minal to ground is greater than 50 pF the timing equations may not represent the pulse width the device generates 2 When an electrolytic capacitor is used for CX a switching diode is often required for standard TTL one-shots to pre- vent high inverse leakage current This switching diode is not needed for the ’LS123 one-shot and should not be used In general the use of the switching diode is not recommended with retriggerable operation Furthermore if a polarized timing capacitor is used on the ’LS123 the negative terminal of the capacitor should be connected to the ‘‘CEXT’’ pin of the device (Figure 1 ) TLF6386 – 8 FIGURE 1 3 For CX ll 1000 pF the output pulse width (TW)isde- fined as follows TW e KRX CX where RX is in kX CX is in pF TW is in ns K 037 4 The multiplicative factor K is plotted as a function of CX below for design considerations TLF6386 – 2 FIGURE 2 3 |
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