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參數(shù)資料
| 型號(hào)： | M74HC123AF1R |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR |
| 中文描述： | 雙RETRIGGERABLE單穩(wěn)態(tài)觸發(fā)器 |
| 文件頁數(shù)： | 4/12頁 |
| 文件大?。?/td> | 503K |
| 代理商： | M74HC123AF1R |
M74HC123
4/12
BLOCK DIAGRAM
(1) Cx, Rx, Dx are external components.
(2) Dx is a clamping diode.
The external capacitor is charged to Vcc in the stand-by-state, i.e. no trigger. When the supply voltage is turned off Cx is discharged mainly
trough an internal parasitic diode(see figures). If Cx is sufficiently large and Vcc decreases rapidly, there will be some possibility of damaging
the I.C. with a surge current or latch-up. If the voltage supply filter capacitor is large enough and Vcc decrease slowly, the surge current is
automatically limited and damage to the I.C. is avoided. The maximum forward current of the parasitic diode is approximately 20 mA. In cases
where Cx is large the time taken for the supply voltage to fall to 0.4 Vcc can be calculated as follows :
t
> (Vcc - 0.7) x Cx/20mA
In cases where t
f
is too short an external clamping diode is required to protect the I.C. from the surge current.
FUNCTIONAL DESCRIPTION
STAND-BY STATE
The external capacitor,Cx, is fully charged to Vcc
in the stand-by state. Hence, before triggering,
transistor Qp and Qn (connected to the Rx/Cx
node) 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.
TRIGGER OPERATION
Triggering occurs when :
1 st) A is "LOW" and B has a falling edge;
2 nd) B is "HIGH" and A has a rising edge;
3 rd) A is "LOW" and B is HIGH and C1 has a
rising edge;
After the multivibrator has been retriggered
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.
When it reaches V
REFL
the output of comparator
C1 becomes low. This in turn reset the flip-flop
and Qn is turned off.
At this point C1 stops functioning but C2 continues
to operate.
The voltage at R/C external begins to rise with a
time constant set by the external components Rx,
Cx.
Triggering the multivibrator causes Q to go high
after internal delay due to the flip-flop and the
gate. Q remains high until the voltage at R/C
external rises again to V
REFH
. At this point C2
output goes low and O goes low. C2 stop
operating. That means that after triggering when
the voltage R/C external returns to V
REFH
the
multivibrator 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 :
tW(OUT) = 0.45 Cx · Rx
RE - TRIGGERED OPERATION
When a second trigger pulse follows the first its
effect will depend on the state of the multivibrator.
If the capacitor Cx is being charged the voltage
level of R/C external falls to V
REFL
again and Q
remains High i.e. the retrigger pulse arrives in a
time shorter than the period Rx · Cx seconds, the
capacitor charging time constant. If the second
trigger pulse is very close to the initial trigger pulse
it is ineffective ; i.e. the second trigger must arrive
in the capacitor discharge cycle to be ineffective;
Hence the minimum time for a second trigger to be
effective depends on Vcc and Cx
RESET OPERATION
CL is normally high. If CL is low, the trigger is not
effective because Q output goes low and trigger
control flip-flop is reset.
Also transistor Op is turned on and Cx is charged
quickly to Vcc. This means if CL input goes low the
IC becomes waiting state both in operating and
non operating state.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| M74HC123AM | 制造商:National Semiconductor 功能描述:74HC123 NSC'91 IN S3E8B |
| M74HC123AM1R | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR |
| M74HC123B1R | 功能描述:單穩(wěn)態(tài)多諧振蕩器 Dual Multivibrator RoHS:否 制造商:Texas Instruments 每芯片元件:1 邏輯系列:LVC 邏輯類型:Monostable Multivibrator 封裝 / 箱體:SSOP-8 傳播延遲時(shí)間:18.6 ns 高電平輸出電流:- 32 mA 低電平輸出電流:32 mA 電源電壓-最大:5.5 V 電源電壓-最小:1.65 V 最大功率耗散: 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝:Reel |
| M74HC123B1R | 制造商:STMicroelectronics 功能描述:IC 74HC CMOS 74HC123 DIP16 6V |
| M74HC123C1R | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR |
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