3A 32V Synchronous Rectified Step-Down

Converter

EC3286

Page 11 of 14

4J23N-Rev.F001

Optional Schottky Diode

During the transition between high-side switch and low-side switch, the body diode of the low-

side power MOSFET conducts the inductor current. The forward voltage of this body diode

is high. An optional Schottky diode may be paralleled between the SW pin and GND pin to

improve overall efficiency. Table 1 lists example Schottky diodes and their Manufacturers.

Input Capacitor

The input current to the step-down converter is discontinuous, therefore a capacitor is required

to supply the AC current to the step-down converter while maintaining the DC input voltage.

Use low ESR capacitors for the best performance. Ceramic capacitors are preferred, but

tantalum or low-ESR electrolytic capacitors may also suffice. Choose X5R or X7R dielectrics

when using ceramic capacitors. Since the input capacitor (C1) absorbs the input switching

current it requires an adequate ripple current rating. The RMS current in the input capacitor

can be estimated by:

choose the input capacitor whose RMS current rating greater than half of the maximum

load current. The input capacitor can be electrolytic, tantalum or ceramic. When using electrolytic

or tantalum capacitors, a small, high quality ceramic capacitor, i.e.

0.1μF, should be placed

as close to the IC as possible. When using ceramic capacitors, make sure that they

have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at

input. The input voltage ripple for low ESR capacitors can be estimated by:

Where C1 is the input capacitance value.

Output Capacitor

The output capacitor is required to maintain the DC output voltage. Ceramic, tantalum, or

low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep

the output voltage ripple low. The output voltage ripple can be estimated by:

Where C2 is the output capacitance value and RESR is the Equivalent series resistance (ESR)

value of the output capacitor.

In the case of ceramic capacitors, the impedance at the switching frequency is dominated by

the

capacitance. The output voltage ripple is mainly caused by the capacitance. For

simplification, the output voltage ripple can be estimated by:

In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at

the switching frequency. For simplification, the output ripple can be approximated to:

Part Number

Voltage/Current

Vendor

B130

30V, 1A

Diodes, Inc.

SK13

30V, 1A

Diodes, Inc.

MBRS130

30V, 1A

International Rectifier