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DM74LS123N View Datasheet(PDF) - National ->Texas Instruments

Part NameDescriptionManufacturer
DM74LS123N Dual Retriggerable One-Shot with Clear and Complementary Outputs National-Semiconductor
National ->Texas Instruments National-Semiconductor
DM74LS123N Datasheet PDF : 6 Pages
1 2 3 4 5 6
Switching Characteristics at VCC e 5V and TA e 25 C
Symbol
Parameters
From (Input)
To (Output)
RL e 2 kX
CL e 15pF
CEXT e 0 pF REXT e 5 kX
CL e 15pF
CEXT e 1000 pF REXT e 10 KX
Min
Max
Min
Max
tPLH
Propagation Delay Time
A to Q
33
Low to High Level Output
tPLH
Propagation Delay Time
B to Q
44
Low to High Level Output
tPHL
Propagation Delay Time
A to Q
45
High to Low Level Output
tPHL
Propagation Delay Time
B to Q
56
High to Low Level Output
tPLH
Propagation Delay Time
Clear to Q
45
Low to High Level Output
tPHL
Propagation Delay Time
Clear to Q
27
High to Low Level Output
tWQ(Min) Minimum Width of Pulse
at Output Q
A or B to Q
200
tW(out) Output Pulse Width
A or B to Q
4
5
Units
ns
ns
ns
ns
ns
ns
ns
ms
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 )
3 For CX ll 1000 pF the output pulse width (TW) is de-
fined as follows
TW e KRX CX
where RX is in kX
CX is in pF
TW is in ns
K 0 37
4 The multiplicative factor K is plotted as a function of CX
below for design considerations
FIGURE 2
TL F 6386 – 2
FIGURE 1
TL F 6386 – 8
3
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