MP1543 — 1.5A, 500KHZ SYNCHRONOUS RECTIFIED STEP-UP CONVERTER

MP1543 Rev. 1.0

www.MonolithicPower.com

7

1/11/2006

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TM

Selecting the Feed-Forward Capacitor

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.

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.

LAYOUT CONSIDERATIONS

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.

MP1543

SW

OUT

FB

GND

EN

4

3

1

2

5

1.8V - 3.2V

EN

MP1543_F02

C3

Up to 220pF

OPTIONAL

3.3V

400mA

Figure 2—3.3V Typical Application Circuit with Feed-Forward Capacitor

MP1543

SW

OUT

FB

GND

EN

4

3

1

2

5

2.5V - 4.2V

D1

EN

MP1543_F02

5V

400mA

Figure 3—5V Typical Application Circuit with External Schottky Diode and Output Disconnect

Not Required