MP2249 – 6V, 3A, 1MHZ, SYNCHRONOUS STEP-DOWN CONVERTER

MP2249 Rev.1.0

www.MonolithicPower.com

7

11/2/2010

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FUNCTION BLOCK DIAGRAM

PVIN

EN

FB

SW

GND

0.6V

1pF

34pF

600k

BIAS &

VOLTAGE

REFERENCE

0.6V

1MHz

OSCILLATOR

ISLOPE

OSC

CONTROL

LOGIC

MAIN

SWITCH

PCH

R

LOW SIDE

GATE DRIVE

SYNCHRONOUS

RECTIFIER

NCH

OUTPUT

DISCHARGE

Internal SS

PG

0.54V

PWM

PVIN

COMP

0.4V

0.4V

Figure 1—Function Block Diagram

OPERATION

The MP2249 is a constant frequency current

mode PWM step-down converter. The MP2249 is

optimized for low voltage, Li-Ion battery powered

applications where high efficiency and small size

are critical. The MP2249 uses an external

resistor divider to set the output voltage from

0.6V to 6V. The device integrates both a main

switch and synchronous rectifier, which provides

high efficiency and eliminates an external

Schottky diode. The MP2249 can achieve 100%

duty cycle. The duty cycle D of a step-down

converter is defined as:

%

100

V

V

%

100

f

T

D

IN

OUT

OSC

ON

×

≈

×

×

=

voltage and VIN is the input voltage

Current Mode PWM Control

Slope compensated current mode PWM control

provides stable switching and cycle-by-cycle

current limit for superior load and line response

and protection of the internal main switch and

synchronous rectifier. The MP2249 switches at a

constant frequency (1MHz) and regulates the

output voltage. During each cycle the PWM

comparator modulates the power transferred to

the load by changing the inductor peak current

based on the feedback error voltage. During

normal operation, the main switch is turned on for

a certain time to ramp the inductor current at

each rising edge of the internal oscillator, and

switched off when the peak inductor current is

above the error voltage. When the main switch is

off, the synchronous rectifier will be turned on

immediately.