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參數(shù)資料
| 型號(hào)： | MC1455 |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | Timing Circuit |
| 中文描述： | 時(shí)序電路 |
| 文件頁(yè)數(shù)： | 5/10頁(yè) |
| 文件大?。?/td> | 147K |
| 代理商： | MC1455 |
MC1455, MC1455B, NCV1455B
http://onsemi.com
5
Figure 13. Representative Circuit Schematic
100
Threshold
Comparator
Trigger
Comparator
FlipFlop
Output
V
CC
Threshold
Trigger
Reset
Discharge
Gnd
Discharge
Reset
100 k
5.0 k
5.0 k
e
4.7 k
c b
7.0 k
6.8 k
3.9 k
b
220
4.7 k
Output
Control Voltage
5.0 k
1.0 k
4.7 k
830
4.7k
10 k
c
GENERAL OPERATION
The MC1455 is a monolithic timing circuit which uses an
external resistor capacitor network as its timing element. It
can be used in both the monostable (oneshot) and astable
modes with frequency and duty cycle controlled by the
capacitor and resistor values. While the timing is dependent
upon the external passive components, the monolithic circuit
provides the starting circuit, voltage comparison and other
functions needed for a complete timing circuit. Internal to the
integrated circuit are two comparators, one for the input
signal and the other for capacitor voltage; also a flipflop and
digital output are included. The comparator reference
voltages are always a fixed ratio of the supply voltage thus
providing output timing independent of supply voltage.
Monostable Mode
In the monostable mode, a capacitor and a single resistor
are used for the timing network. Both the threshold terminal
and the discharge transistor terminal are connected together
in this mode (refer to circuit in Figure 14). When the input
voltage to the trigger comparator falls below 1/3 V
CC
, the
comparator output triggers the flipflop so that its output
sets low. This turns the capacitor discharge transistor “off”
and drives the digital output to the high state. This condition
allows the capacitor to charge at an exponential rate which
is set by the RC time constant. When the capacitor voltage
reaches 2/3 V
CC
, the threshold comparator resets the
flipflop. This action discharges the timing capacitor and
returns the digital output to the low state. Once the flipflop
has been triggered by an input signal, it cannot be retriggered
until the present timing period has been completed. The time
that the output is high is given by the equation t = 1.1 R
A
C.
Various combinations of R and C and their associated times
are shown in Figure 16. The trigger pulse width must be less
than the timing period.
A reset pin is provided to discharge the capacitor, thus
interrupting the timing cycle. As long as the reset pin is low,
the capacitor discharge transistor is turned “on” and
prevents the capacitor from charging. While the reset
voltage is applied the digital output will remain the same.
The reset pin should be tied to the supply voltage when not
in use.
Figure 14. Monostable Circuit
R
L
+V
CC
(5.0 V to 15 V)
Reset
V
CC
8
Discharge
7
6
5
Threshold
Control
Voltage
0.01 F
1
2
Trigger
Output
3
4
R
A
R
L
MC1455
C
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