参数资料
| 型号： | MIC1557YM5 TR |
| 厂商： | Micrel Inc |
| 文件页数： | 3/17页 |
| 文件大小： | 0K |
| 描述： | IC OSC MONO TIMING 5MHZ SOT23-5 |
| 标准包装： | 1 |
| 系列： | IttyBitty® |
| 类型： | 555 型，计时器/振荡器（单路） |
| 频率： | 5MHz |
| 电源电压： | 2.7 V ~ 18 V |
| 电流 - 电源： | 350µA |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | SC-74A，SOT-753 |
| 包装： | 标准包装 |
| 供应商设备封装： | SOT-23-5 |
| 安装类型： | 表面贴装 |
| 产品目录页面： | 1113 (CN2011-ZH PDF) |
| 其它名称： | 576-1055-6 |
Micrel, Inc.
MIC1555/1557
March 11, 2014
11
Revision 6.0
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
(CT) is charged through a resistor (RT) connected to the
output of an MIC1555, the trip point is approximately
1.1RTCT (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
oscillations 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 (DT) in parallel with (RT) resets
the one-shot quickly.
Figure 1. One-Shot Diagram
The period of a monostable circuit is:
t = k2 RC
where:
t = period (s)
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 comparator inputs, threshold and trigger (T/T), tied
together internally. 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 (RT) is connected from the output to a
grounded timing capacitor (CT), 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
propagation
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 (RA), and a second resistor (RB) in series with an
opposite facing switching diode and resistor connected in
parallel (see Figure 2). The frequency is then made up of
two
components,
the
charging
time
(tA) and the
discharging time (tB) tA = 0.7RACT and tB = 0.7RBCT. The
frequency is the reciprocal of the sum of the two times tA
+ tB, so the total time is 1.4RTCT. The first half-cycle of an
astable, after power-on or CS enable, is lengthened since
the capacitor is charging from ground instead of the 1/3
input trigger trip voltage, to 1.1RC, the same as a
monostable pulse.
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