MIC2289-15YML datasheet(5/10 Pages) MICREL

Part #	MIC2289-15YML

Description	White LED Driver Internal Schottky Diode and OVP

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Manufacturer	MICREL [Micrel Semiconductor]

Direct Link	http://www.micrel.com

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5 / 10 page

Micrel, Inc.

MIC2289

July 2007

5

M9999-071007

Functional Diagram

GND

VREF

PWM

Generator

Ramp

Generator

1.2MHz

Oscillator

SW

EN

FB

OUT

VIN

95mV

gm

OVP

S

MIC2289 Block Diagram

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, gm 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 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.

The gm 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 gm 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, maintaining the constant

frequency current-mode PWM control. The LED is set by

the feedback resistor:

FB

LED

R

95mW

I

=

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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MIC2289-15YML Datasheet(PDF) 5 Page - Micrel Semiconductor

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