Datasheet

74HC_HCT123 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 9 — 19 January 2015 10 of 25
NXP Semiconductors
74HC123; 74HCT123
Dual retriggerable monostable multivibrator with reset
[1] t
pd
is the same as t
PHL
and t
PLH
; t
t
is the same as t
THL
and t
TLH
[2] For other R
EXT
and C
EXT
combinations see Figure 7. If C
EXT
> 10 nF, the next formula is valid.
t
W
=K R
EXT
 C
EXT
, where:
t
W
= typical output pulse width in ns;
R
EXT
= external resistor in k;
C
EXT
= external capacitor in pF;
K = constant = 0.45 for V
CC
= 5.0 V and 0.55 for V
CC
=2.0V.
The inherent test jig and pin capacitance at pins 15 and 7 (nREXT/CEXT) is approximately 7 pF.
[3] The time to retrigger the monostable multivibrator depends on the values of R
EXT
and C
EXT
. The output pulse width will only be
extended when the time between the active-going edges of the trigger input pulses meets the minimum retrigger time. If C
EXT
>10 pF,
the next formula (at V
CC
= 5.0 V) for the setup time of a retrigger pulse is valid:
t
rtrig
= 30 + 0.19  R
EXT
 C
EXT
0.9
+13 R
EXT
1.05
, where:
t
rtrig
= retrigger time in ns;
C
EXT
= external capacitor in pF; R
EXT
= external resistor in k.
The inherent test jig and pin capacitance at pins 15 and 7 (nREXT/CEXT) is 7 pF.
[4] When the device is powered-up, initiate the device via a reset pulse, when C
EXT
<50pF.
[5] C
PD
is used to determine the dynamic power dissipation (P
D
in W).
P
D
=C
PD
 V
CC
2
 f
i
+ (C
L
 V
CC
2
 f
o
) + 0.75  C
EXT
 V
CC
2
 f
o
+D 16  V
CC
where:
f
i
= input frequency in MHz;
f
o
= output frequency in MHz;
D = duty factor in %;
C
L
= output load capacitance in pF;
V
CC
= supply voltage in V;
C
EXT
= timing capacitance in pF;
(C
L
 V
CC
2
 f
o
) sum of outputs.
t
W
pulse width V
CC
= 4.5 V
nA
LOW; see Figure 10 20 3 - 25 - 30 - ns
nB HIGH; see Figure 10
20 5 - 25 - 30 - ns
nRD
LOW; see Figure 11 20 7 - 25 - 30 - ns
nQ HIGH and nQ
LOW;
V
CC
=5.0V;
see Figure 10 and 11
[2]
C
EXT
= 100 nF;
R
EXT
= 10 k
-450- - - - - s
C
EXT
= 0 pF;
R
EXT
=5k
-75- - - - -ns
t
rtrig
retrigger time nA,nB; C
EXT
= 0 pF;
R
EXT
= 5 k; V
CC
= 5.0 V;
see Figure 10
[3][4]
-110- - - - - ns
R
EXT
external timing
resistor
V
CC
= 5.0 V; see Figure 7 2-1000- - - -k
C
EXT
external timing
capacitor
V
CC
= 5.0 V; see Figure 7
[4]
--- - - - -pF
C
PD
power
dissipation
capacitance
per monostable;
V
I
= GND to V
CC
 1.5 V
[5]
-56- - - - -pF
Table 7. Dynamic characteristics
…continued
Voltages are referenced to GND (ground = 0 V); C
L
= 50 pF unless otherwise specified; for test circuit see Figure 12.
Symbol Parameter Conditions 25 C 40 C to +85 C 40 C to +125 C Unit
Min Typ Max Min Max Min Max