Datasheet

MIC2288
DS20006034B-page 10  2018 Microchip Technology Inc.
4.0 FUNCTIONAL DESCRIPTION
The MIC2288 is a constant frequency, PWM current
mode boost regulator. See the Functional Block
Diagram. The MIC2288 is composed of an oscillator,
slope compensation ramp generator, current amplifier,
g
m
error amplifier, PWM generator, and a 1A bipolar
output transistor. The oscillator generates a 1.2 MHz
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 g
m
error amplifier measures the feedback voltage
through the external feedback resistors and amplifies
the error between the detected signal and the 1.24V
reference voltage. The output of the g
m
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.