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參數(shù)資料
| 型號： | MIC2289 |
| 廠商： | Micrel Semiconductor,Inc. |
| 元件分類： | LED驅(qū)動器 |
| 英文描述： | 2mm 】 2mm White LED Driver with Internal Schottky Diode and OVP |
| 中文描述： | 2毫米】2mm的白光LED內(nèi)部肖特基二極管和OVP驅(qū)動器 |
| 文件頁數(shù)： | 5/9頁 |
| 文件大?。?/td> | 88K |
| 代理商： | MIC2289 |
August, 2004
5
M9999-081104
MIC2289
Functional Diagram
Micrel
Functional Description
The MIC2289 is a constant frequency, PWM current mode
boost regulator. The block diagram is shown above. The
MIC2289 is composed of an oscillator, slope compensation
ramp generator, current amplifier, g
m
error amplifier, PWM
generator, 500mA bipolar output transistor, and Schottky
rectifier diode. The oscillator generates a 1.2MHz clock. The
clock
’
s two functions are to trigger the PWM generator that
turns on the output transistor and to reset the slope compen-
sation ramp generator. The current amplifier is used to
measure the switch current by amplifying the voltage signal
from the internal sense resistor. The output of the current
amplifier is summed with the output of the slope compensa-
tion ramp generator. This summed current-loop signal is fed
to one of the inputs of the PWM generator.
GND
V
REF
PWM
Generator
Ramp
Generator
1.2MHz
Oscillator
SW
EN
FB
OUT
VIN
95mV
g
m
OVP
Σ
MIC2289 Block Diagram
The g
m
error amplifier measures the LED current through the
external sense resistor and amplifies the error between the
detected signal and the 95mV reference voltage. The output
of the g
m
error amplifier provides the voltage-loop signal that
is fed to the other input of the PWM generator. When the
current-loop signal exceeds the voltage-loop signal, the
PWM generator turns off the bipolar output transistor. The
next clock period initiates the next switching cycle, maintain-
ing the constant frequency current-mode PWM control. The
LED is set by the feedback resistor:
I
LED
=
95mv
R
FB
The Enable pin shuts down the output switching and disables
control circuitry to reduce input current to leakage levels.
Enable pin input current is zero at zero volts.
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