July 2005

5

M9999-070105

MIC2292/93

Micrel, Inc.

Functional Description

The MIC2292/93 is a constant frequency, PWM current mode

boost regulator. The block diagram is shown above. The

MIC2292/93iscomposedofanoscillator,slopecompensation

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.

Functional Diagram

MIC2292/93 Block Diagram

external sense resistor and amplifies the error between the

detected signal and the 95mV reference voltage. The output

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:

95mv

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

OUT

VIN

95mV

OVP*

S

1.6MHz

or