UM3501_15 Datasheet, PDF(8/11 Page) Union Semiconductor, Inc. – 600mA, 1.2MHz, Synchronous Step-Down DC-DC Converter

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UM3501_15 Datasheet, PDF (8/11 Pages) Union Semiconductor, Inc. – 600mA, 1.2MHz, Synchronous Step-Down DC-DC Converter

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UM3501

Inductor Selection

A 1ÂµH to 10ÂµH inductor with DC current rating at least 25% higher than the maximum load

current is recommended for most applications. For best efficiency, the inductor DC resistance

shall be<200mâ¦.

For most designs, the inductance value can be derived from the following equation:

L ï½ VOUT ï´ (VIN ï VOUT )

VIN ï´ ïI L ï´ fOSC

Where âIL is the inductor ripple current. Choose inductor ripple current approximately 30% of the

maximum load current, 600mA.

The maximum inductor peak current is:

I L(MAX)

ï½

I LOAD ï«

ïI L

Under light load conditions below 100mA, larger inductance is recommended for improved

efficiency.

Input Capacitor Selection

The input capacitor reduces the surge current drawn from the input and switching noise from the

device. The input capacitor impedance at the switching frequency shall be less than input source

impedance to prevent high frequency switching current passing to the input. Ceramic capacitors

with X5R or X7R dielectrics are highly recommended because of their low ESR and small

temperature coefficients. For most applications, a 4.7ÂµF capacitor is sufficient.

Output Capacitor Selection

The output capacitor keeps output voltage ripple small and ensures regulation loop stable. The

output capacitor impedance shall be low at the switching frequency. Ceramic capacitor with X5R

or X7R dielectrics are recommended. The output ripple âVOUT is approximately:

ïVOUT

ï£

VOUT ï´ (VIN ï VOUT

VIN ï´ fOSC ï´ L

)

ï´

ï§ï§ï¨ï¦

ESR

ï«

8ï´

f OSC

ï´ C3 ï·ï·ï¸ï¶

Layout Guidance

When laying out the PC board, the following suggestions should be taken to ensure proper

operation of the UM3501.

1. The power traces, including the GND trace, the SW trace and the VIN trace should be kept

short, direct and wide to allow large current flow.

2. Connect the input capacitor C1 to the VIN pin as closely as possible to get good power filter

effect.

3. Keep the switching node, SW, away from the sensitive FB node.

4. Do not trace signal line under inductor.

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http://www.union-ic.com Rev.06 Feb.2015

8/11

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