TM
MP1543 — 1.5A, 500KHZ SYNCHRONOUS RECTIFIED STEP-UP CONVERTER
Selecting the Feed-Forward Capacitor
LAYOUT CONSIDERATIONS
A feed-forward capacitor C3 in parallel with the
high-side resistor R1 can be added to improve
the output ripple at discontinuous conduction
mode and the load transient response (see
Figure 2). Up to 220pF for this capacitor is
recommended for 3.3V output applications.
High frequency switching regulators require
very careful layout for stable operation and low
noise. All components must be placed as close
to the IC as possible. All feedback components
must be kept close to the FB pin to prevent
noise injection on the FB pin trace. The ground
return of C1 and C2 should be tied close to the
GND pin. See the MP1543 demo board layout
for reference.
Selecting the Schottky Diode
A Schottky diode D1 in parallel with the high-
side P-Channel MOSFET is necessary to clamp
the SW node to a safe level for outputs of 4V or
above. A 0.5A, 20V Schottky diode can be used
for this purpose. See Figure 3.
V
IN
1.8V - 3.2V
4
SW
3
1
V
3.3V
400mA
OUT
FB
OUT
C3
5
Up to 220pF
OPTIONAL
EN
EN
MP1543
GND
2
MP1543_F02
Figure 2—3.3V Typical Application Circuit with Feed-Forward Capacitor
D1
V
IN
2.5V - 4.2V
4
SW
3
1
V
5V
400mA
OUT
FB
OUT
5
EN
EN
MP1543
GND
2
MP1543_F02
Figure 3—5V Typical Application Circuit with External Schottky Diode and Output Disconnect
Not Required
MP1543 Rev. 1.0
1/11/2006
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2006 MPS. All Rights Reserved.
7
MPS [ MONOLITHIC POWER SYSTEMS ]
