MIC2196

Micrel

MIC2196

6

August 2004

Functional Description

The MIC2196 is a BiCMOS, switched-mode multi-topology

controller. It will operate most low-side drive topologies

including boost, SEPIC, flyback and forward. The controller

has a low impedance driver capable of switching large N-

channel MOSFETs. It features multiple frequency and duty

cycle settings. Current mode control is used to achieve

superior transient line and load regulation. An internal correc-

tive ramp provides slope compensation for stable operation

above a 50% duty cycle. The controller is optimized for high-

efficiency, high-performance DC-DC converter applications.

Figure 1 shows a block diagram of the MIC2196 configured

as a PWM boost converter.

Functional Diagram

Osc

Error

Amplifier

0.11V

D1

L1

fs/4

Control

Bias

PWM

Comparator

GND

Overcurrent

Comparator

Frequency

Foldback

fs/4

Overcurrent Reset

Corrective

Ramp

On

Gain = 3.7

CS

4

OUTN

7

V

IN

8

V

fb

6

GND

2

V

DD

5

COMP

2

EN/UVLO

3

gm = 0.0002

Gain = 20

0.3V

100k

R2

R1

Figure 1. MIC2196 Block Diagram

The switching cycle starts when OUTN goes high and turns

on the low-side, N-channel MOSFET, Q1. The V

MOSFET is equal to V

inductor. The inductor current flows through the current

sense resistor, R

amplified and combined with an internal ramp for stability.

This signal is compared with the error voltage signal from the

error amplifier. When the current signal equals the error

voltage signal, the low-side MOSFET is turned off. The

inductor current then flows through the diode, D1, to the

output. The MOSFET remains off until the beginning of the

next switching cycle.