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參數資料
| 型號： | MIC1557 |
| 廠商： | Micrel Semiconductor,Inc. |
| 英文描述： | IttyBitty RC Oscillator(IttyBitty技術CMOS RC振蕩器) |
| 中文描述： | IttyBitty RC振蕩器（IttyBitty技術的CMOS鋼筋混凝土振蕩器） |
| 文件頁數： | 6/8頁 |
| 文件大?。?/td> | 166K |
| 代理商： | MIC1557 |
MIC1555/1557
Application Information
Basic Monostable (One-Shot) Circuit
A monostable oscillator produces a single pulse each time
that it is triggered, and is often referred to as a “one-shot”. The
pulse width is constant, while the time between pulses
depends on the trigger input. One-shots are generally used
to “stretch” incoming pulses, of varying widths, to a fixed
width. The IttyBitty MIC1555 is designed for monostable
operation, but may also be connected to provide astable
oscillations. The pulse width is determined by the time it takes
to charge a capacitor from ground to a comparator trip point.
If the capacitor (C
T
) is charged through a resistor (R
T
)
connected to the output of an MIC1555, the trip point is
approximately 1.1RC
T
(the same time as the initial power-on
cycle of an astable circuit.) If the trigger pulse of an MIC1555
remains low longer than the output pulse width, short oscilla-
tions may be seen in the output of a one-shot circuit, since the
threshold pin has precedence over the trigger pin. These
occur since the output goes low when the threshold is
exceeded, and then goes high again as the trigger function is
asserted. AC coupling the input with a series capacitor and
a pull-up resistor, with an RC time constant less than the
pulse width, will prevent these short oscillations. A diode (D
T
)
in parallel with (R
T
) resets the one-shot quickly.
Micrel
MIC1555/1557
6
October 1998
CS
OUT
THR
TRG
VS
GND
D
T
R
T
OUT
3
C
IN
R
PU
C
T
MIC1555
Trigger
1
3
V
IN
t
ON
= 1.1R
T
C
T
2.7V to 18V
1
2
4
5
Figure 1. One-Shot Diagram
The period of a monostable circuit is:
t = k
2
RC
where:
t = period (s)
k
2
= constant [from Typical Characteristics graph]
R = resistance (
)
C = capacitance (F)
Basic Astable (Oscillator) Circuits
An astable oscillator switches between two states, “on” and
“off”, producing a continuous square wave. The IttyBitty
MIC1557 is optimized for this function, with the two compara-
tor inputs, threshold and trigger (T/T), tied together internally.
Chip select (CS) is brought out to allow on-off control of the
oscillator.
The MIC1555 may also be used as an astable oscillator by
tying the threshold and trigger pins together, forming a T/T
pin. If a resistor (R
T
) is connected from the output to a
grounded timing capacitor, (C
T
) the voltage at their junction
will ramp up from ground when the output goes high. If the T/
T pin is connected to this junction, the output will switch low
when the ramp exceeds
2
3
of the input voltage. The junction's
voltage ramps down toward ground while the output is low.
When the ramp is below
1
3
of the input voltage, the output
switches to high, and the junction ramps up again.
The continuing frequency of an MIC1555/7 astable oscillator
depends on the RC time constant, and is approximately 0.7/
RC below 1MHz. At frequencies above 1MHz the RC
multiplier increases as capacitance is decreased, and propa-
gation delay becomes dominant. Non-symmetrical oscillator
operation is possible at frequencies up to 5MHz.
If a duty cycle other than 50% is desired, a low-power signal
diode may be connected in series with the timing resistor
(R
A
), and a second resistor (R
B
) in series with an opposite
facing diode connected in parallel. The frequency is then
made up of two components, the charging time (t
A
) and the
discharging time (t
B
) t
A
= 0.7R
A
C and t
B
= 0.7R
B
C. The
frequency is the reciprocal of the sum of the two times t
A
+ t
B
,
so the total time is 1.4R
T
C
T
. The first half-cycle of an astable,
after power-on or CS enable, is lengthened since the capaci-
tor is charging from ground instead of the 13 input trigger trip
voltage, to 1.1RC, the same as a monostable pulse.
R
A
1k to 1M
CS
OUT
T/T
VS
GND
OUT
5
MIC1557
2.7V to 18V
C
B
R
E
C
100pF to 10μF
3
2
4
1
CS
t = 0.7(R
A
+R
B
)C
T
t
R
B
Figure 2. Oscillator Diagram
The MIC1555 or MIC1557 can be used to construct an
oscillator.
The frequency of an astable oscillator is:
f
1
k RC
=
where:
f = frequency (Hz)
k
1
= constant [from Typical Characteristics graph]
R = resistance (
)
C = capacitance (F)
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相關代理商/技術參數 |
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| MIC1557BM5 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| MIC1557BM5 TR | 功能描述:IC OSC MONO TIMING 5MHZ SOT23-5 RoHS:否 類別:集成電路 (IC) >> 時鐘/計時 - 可編程計時器和振蕩器 系列:IttyBitty® 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:45 系列:- 類型:溫度 - 補償晶體振蕩器（TCXO） 計數:- 頻率:25MHz 電源電壓:3.135 V ~ 3.465 V 電流 - 電源:1.5mA 工作溫度:-40°C ~ 85°C 封裝/外殼:16-SOIC（0.295"，7.50mm 寬） 包裝:管件 供應商設備封裝:16-SOIC W 安裝類型:表面貼裝 |
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| MIC1557YM5 | 制造商:Rochester Electronics LLC 功能描述: 制造商:RF Micro Devices Inc 功能描述: |
| MIC1557YM5 TR | 功能描述:計時器和支持產品 2.7V to 18V, "555" RC Timer/Oscillator with Shutdown in SOT23-5 RoHS:否 制造商:Micrel 類型:Standard 封裝 / 箱體:SOT-23 內部定時器數量:1 電源電壓-最大:18 V 電源電壓-最小:2.7 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 |
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