August, 2004

5

M9999-081204

MIC2292/93

Micrel

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 compensa-

tion ramp generator, current amplifier, g

PWM 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 compen-

sation 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 compensa-

tion ramp generator. This summed current-loop signal is fed

to one of the inputs of the PWM generator.

Functional Diagram

MIC2292/93 Block Diagram

The g

external sense resistor and amplifies the error between the

detected signal and the 95mV reference voltage. The output

of the g

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:

I

95mv

R

FB

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.

GND

PWM

Generator

Ramp

Generator

2.0MHz

Oscillator

SW

EN

FB

OVP*

VIN

95mV

OVP*

Σ

1.6MHz

or