mic2292-34yml Micrel Semiconductor, mic2292-34yml Datasheet - Page 5

• Manufacturer Part Number: mic2292-34yml
• Description: Mic2292/mic2293 High Frequency Pwm White Led Drivers With Internal Schottky Diode And Ovp
• Manufacturer: Micrel Semiconductor

Functional Diagram
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 compensation
ramp generator, current amplifier, g
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 compensation
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 compensation ramp
generator. This summed current-loop signal is fed to one of
the inputs of the PWM generator.
July 2005
MIC2292/93
V
VIN
REF
95mV
m
FB
OVP*
error amplifier, PWM
g
m
MIC2292/93 Block Diagram
Oscillator
1.6MHz
2.0MHz
or
5
The g
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.
Generator
Generator
Ramp
PWM
EN
m
I
S
LED
error amplifier measures the LED current through the
m
=
error amplifier provides the voltage-loop signal
95mv
R
FB
OUT
SW
GND
M9999-070105
Micrel, Inc.