MIC2295 Datasheet, PDF (8/13 Pages) Micrel Semiconductor – High Power Density 1.2A Boost Regulator

Micrel
MIC2295
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.
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 constant frequency
current-mode PWM control
VIN FB OVP*
OVP*
g_m
V_REF
1.24V
EN
MIC2295
SW
PWM
Generator
Σ
CA
1.2MHz
Oscillator
Ramp
Generator
*OVP available on MLF^TM package option only.
MIC2295 Block Diargam
GND
July 2004
8
M9999-052402
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