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参数资料
| 型号： | M54HC423F1R |
| 厂商： | 意法半导体 |
| 英文描述： | PLUG, D, PCB, R/A, 15WAY; Connector type:D Sub, Filtered; Gender:Plug; Ways, No. of:15; Mating cycles, No. of:100; Termination method:PCB; Material, contact:Turned Copper alloy; Plating, contact:Gold over Nickel; Material:Steel; RoHS Compliant: Yes |
| 中文描述： | 双RETRIGGERABLE单稳态触发器 |
| 文件页数： | 3/14页 |
| 文件大小： | 290K |
| 代理商： | M54HC423F1R |
BLOCK DIAGRAM
Note:
(1)Cx, Rx, Dxare external components.
(2)Dx isa clamping diode.
Theexternal capacitor ischarged toV
CC
inthestand-by state, i.e.no trigger.Whenthesupply voltageisturned off Cxisdischarged mainly
through an internal parasitic diode (see figures). IfCx is sufficiently large and V
CC
decreases rapidy, there will besomepossibility ofda-
maging theI.C.witha surge currentor latch-up. If the voltage supply filtercapacitor is large enough and V
CC
decrease slowly,thesurge
current is automatically limited and damage theI.C. isavoided. Themaximum forward current of the parasitic diode isapproximately 20
mA.In cases where Cx islarge the time takenforthe supply voltage to fallto 0.4 V
CC
canbecalculated as follows:
t
f
≥
(V
CC
– 0.7)
Cx/20mA
Incases where t
f
istooshort an external clamping diode is required toprotect theI.C. fromthesurge current.
FUNCTIONAL DESCRIPTION
STAND-BY STATE
The external capacitor, Cx, is fully charged to V
CC
in the stand-by state. Hence, before triggering,
transistor QpandQn(connected totheRx/Cxnode)
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.
TRIGGEROPERATION
Triggering occurswhen :
1 st) A is ”low” and B has a falling edge ;
2 nd) B is ”high” and A has a rising edge ;
3 rd) AislowandBishigh andC1 hasa risingedge.
After the
multivibrator
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.
has
been retriggered
When itreaches V
REFL
theoutput of comparator C1
becomeslow.Thisinturnresets theflip-flop and Qn
is turned off.
At this point C1 stops functioning but C2 continues
to operate.
ThevoltageatR/Cexternalbegins torise withatime
constant set by the external components Rx, Cx.
Triggering the multivibratorcausesQtogohigh after
internal delay due to the flip-flop and the gate. Q
remains high until the voltage at R/C external rises
againto V
REFH
. Atthis point C2output goeslowand
O goes low. C2 stop operating. That means that
after triggering when the voltage R/C external
returns to V
REFH
themultivibrator 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 :
t
W(OUT)
= 0.46 Cx
Rx (HC423)
t
W(OUT)
= Cx
Rx (HC423A)
M54/M74HC423/423A
3/14
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