MIC2287C MICREL [Micrel Semiconductor], MIC2287C Datasheet - Page 5

• Manufacturer Part Number: MIC2287C
• Manufacturer: MICREL [Micrel Semiconductor]

Functional Diagram
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 amplifier, g
generator, and a 500mA bipolar output transistor. The oscil-
lator 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 compensation ramp genera-
tor. The current amplifier is used to measure the switch cur-
rent by amplifying the voltage signal from the internal sense
resistor. The output of the current amplifier 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 g
February 2006
MIC2287C
m
error amplifier measures the LED current through the
*
OVP available on MLF
V
VIN
REF
95mV
FB
OVP*
m
error amplifier, PWM
OVP*
g
TM
m
package option only
Oscillator
1.2MHz
MIC2287C Block Diagram
5
Generator
Generator
external sense resistor and amplifies the error between the
detected signal and the 95mV reference voltage. The output
of the g
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:
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.
Ramp
PWM
EN

I
LED
m
=
error amplifier provides the voltage-loop signal
95mv
R
FB
SW
GND
M0510-020906
Micrel