MIC2290(2004) Просмотр технического описания (PDF) - Micrel

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MIC2290
(Rev.:2004)

2mm × 2mm PWM Boost Regulator with Internal Schotty Diode

Micrel 

MIC2290

Functional Diagram

VIN FB

EN

OUT

OVP

gm

VREF

1.24V

PWM

Generator

Σ

CA

1.2MHz

Oscillator

Ramp

Generator

Figure 1. MIC2290 Block Diagram

SW

GND

Micrel

Functional Description

The MIC2290 is a constant frequency, PWM current mode

boost regulator. The block diagram is shown in Figure 1. The

MIC2290 is composed of an oscillator, slope compensation

ramp generator, current amplifier, gm error amplifier, PWM

generator, and a 0.5A bipolar output transistor. 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 feedback voltage through

the external feedback resistors and amplifies the error be-

tween the detected signal and the 1.24V 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 sig-

nal, 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 con-

trol.

August 2004

7

M9999-081104

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