Micrel

MIC2296

January 2010

6

M9999-011310

Functional Description

The MIC2296 is a high power density, PWM dc/dc boost

regulator. The block diagram is shown in Figure 1. The

MIC2296

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 600kHz 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.

through the external feedback resistors and amplifies the

error between the detected signal and the 1.24V reference

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

GND

CA

PWM

Generator

Ramp

Generator

600kHz

Oscillator

SW

EN

FB

OVP*

VIN

1.24V

OVP*

MIC2296

Figure 1. MIC2296 Block Diagram