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MIC2292 Datasheet(PDF) 5 Page - Micrel Semiconductor

Part No. MIC2292
Description  High Frequency PWM White LED Drivers with Internal Schottky Diode and OVP
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Maker  MICREL [Micrel Semiconductor]
Homepage  http://www.micrel.com
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MIC2292 Datasheet(HTML) 5 Page - Micrel Semiconductor

   
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August, 2004
5
M9999-081204
MIC2292/93
Micrel
Functional Description
The MIC2292/93 is a constant frequency, PWM current mode
boost regulator. The block diagram is shown above. The
MIC2292/93 is composed of an oscillator, slope compensa-
tion ramp generator, current amplifier, g
m error amplifier,
PWM generator, 500mA bipolar output transistor, and Schottky
rectifier diode. The oscillator generates a 1.6MHz clock for
the MIC2292 and a 2.0MHz clock for the MIC2293. The
clocks' 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.
Functional Diagram
MIC2292/93 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.
GND
VREF
PWM
Generator
Ramp
Generator
2.0MHz
Oscillator
SW
EN
FB
OVP*
VIN
95mV
*OVP available on MLFTM package option only
gm
OVP*
Σ
1.6MHz
or


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