Micrel

MIC2295

July 2004

M9999-052402

(408) 955-1690

8

Functional Description

The MIC2295 is a high power density, PWM dc/dc

boost regulator. The block diagram is shown in

Figure 1. The MIC2295 is composed of an oscillator,

slope compensation ramp generator, current

amplifier, gm error amplifier, PWM generator, and a

1.2A 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.

voltage through the external feedback resistors and

amplifies the error between the detected signal and

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 constant frequency

current-mode PWM control

GND

CA

PWM

Generator

Ramp

Generator

1.2MHz

Oscillator

SW

EN

FB

OVP*

VIN

1.24V

OVP*

Σ

MIC2295

MIC2295 Block Diargam