MIC2193

Micrel

M9999-042704

6

April 2004

Functional Characteristics

Controller Overview and Functional Description

The MIC2193 is a BiCMOS, switched mode, synchronous

step down (buck) converter controller. It uses both N- and P-

channel MOSFETs, which allows the controller to operate at

100% duty cycle and eliminates the need for a high-side drive

boot-strap circuit. 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 is a block diagram of the MIC2193 configured as a

synchronous buck converter. At the beginning of the switch-

Functional Diagram

FREQUENCY

FOLDBACK

ERROR

AMP

PWM

COMPARATOR

OVERCURRENT

COMPARATOR

L1

CURRENT

SENSE

AMP

0.3V

100k

gm = 0.0002

gain = 20

fs/4

COMP

ON

GAIN

3

RESET

VREF

1.245V

2

VDD

SLOPE

COMPENSATION

∑

OSC

fs/4

CONTROL

BIAS

CSL

4

VIN

OUTP

8

OUTN

7

Q2

Q1

D1

FB

3

VIN

1

GND

6

Figure 1. MIC2193 Block Diagram

ing cycle, the OUTP pin pulls low and turns on the high-side

P-Channel MOSFET, Q1. Current flows from the input to the

output through the current sense resistor, MOSFET, and

inductor. The current amplitude increases, controlled by the

inductor. The voltage developed across the current sense

resistor, R

bined with an internal ramp for stability. This signal is com-

pared to the output of the error amplifier. When the current

signal equals the error voltage signal, the P-channel MOSFET

is turned off. The inductor current flows through the diode, D1,

until the synchronous, N-channel MOSFET turns on. The

voltage drop across the MOSFET is less than the forward

voltage drop of the diode, which improves the converter

efficiency. At the end of the switching period, the synchro-

nous MOSFET is turned off and the switching cycle repeats.