MP2249 – 6V, 3A, 1MHZ, SYNCHRONOUS STEP-DOWN CONVERTER
FUNCTION BLOCK DIAGRAM
PVIN
PVIN
BIAS &
VOLTAGE
REFERENCE
0.6V
0.4V
1MHz
OSCILLATOR
EN
ISLOPE
MAIN
SWITCH
PCH
OSC
CONTROL
LOGIC
PWM
Internal SS
FB
0.6V
COMP
SW
600k
34pF
0.4V
SYNCHRONOUS
RECTIFIER
NCH
R
LOW SIDE
GATE DRIVE
1pF
PG
OUTPUT
DISCHARGE
0.54V
GND
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:
D
=
T
ON
×
f
OSC
×
100%
≈
V
OUT
×
100%
V
IN
Where T
ON
is the main switch on time, f
OSC
is the
oscillator frequency (1MHz), V
OUT
is the output
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.
MP2249 Rev.1.0
11/2/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
7
MPS [ MONOLITHIC POWER SYSTEMS ]
