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MIC2287CYD5TR Datasheet, PDF (5/9 Pages) Micrel Semiconductor – 1.2MHz PWM White LED Driver with OVP in 2mm × 2mm MLF™ and Thin SOT-23 | |||
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MIC2287C
Functional Diagram
VIN FB OVP*
EN
OVP*
gm
VREF
95mV
PWM
Generator
ï
1.2MHz
Oscillator
Ramp
Generator
*OVP available on MLFTM package option only
MIC2287C Block Diagram
SW
GND
Micrel
Functional Description
The MIC2287C is a constant frequency, PWM current mode
boost regulator. The block diagram is shown above. The
MIC2287C is composed of an oscillator, slope compensation
ramp generator, current ampliï¬er, gm error ampliï¬er, PWM
generator, and a 500mA bipolar output transistor. The oscil-
lator generates a 1.2MHz clock. The clockâs two functions
are to trigger the PWM generator that turns on the output
transistor and to reset the slope compensation ramp genera-
tor. The current ampliï¬er is used to measure the switch cur-
rent by amplifying the voltage signal from the internal sense
resistor. The output of the current ampliï¬er is summed with
the output of the slope compensation ramp generator. This
summed current-loop signal is fed to one of the inputs of the
PWM generator.
The gm error ampliï¬er measures the LED current through the
external sense resistor and ampliï¬es the error between the
detected signal and the 95mV reference voltage. The output
of the gm error ampliï¬er 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:
95mv
ILED = RFB
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.
February 2006
5
M0510-020906
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