MIC2288 Micrel Semiconductor, MIC2288 Datasheet - Page 6

• Manufacturer Part Number: MIC2288
• Description: 1A 1.2 MHZ PWM BOOST CONVERTER IN THIN SOT 23 AND 2 X MLF
• Manufacturer: Micrel Semiconductor

MIC2288
Functional Diagram
Functional Description
The MIC2288 is a constant frequency, PWM current mode
boost regulator. The block diagram is shown in Figure 1. The
MIC2288 is composed of an oscillator, slope compensation
ramp generator, current amplifier, g
generator, and a 1A 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.
M9999-021904
*
OVP available on MLF
VIN
1.24V
FB
m
OVP*
error amplifier, PWM
OVP*
g
TM
Figure 1. MIC2288 Block Diagram
m
package option only.
Oscillator
1.2MHz
6
The g
the external feedback resistors and amplifies the error be-
tween the detected signal and the 1.24V reference voltage.
The output of the g
signal that is fed to the other input of the PWM generator.
When the current-loop signal exceeds the voltage-loop sig-
nal, 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 con-
trol.
Generator
Generator
Ramp
PWM
EN
m
error amplifier measures the feedback voltage through
CA
m
error amplifier provides the voltage-loop
SW
GND
February 2004
Micrel