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DM74LS123 Datasheet(PDF) 3 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. DM74LS123
Description  Dual Retriggerable One-Shot with Clear and Complementary Outputs
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Maker  NSC [National Semiconductor (TI)]
Homepage  http://www.national.com
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DM74LS123 Datasheet(HTML) 3 Page - National Semiconductor (TI)

   
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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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