UM3510 Datasheet, PDF (8/10 Pages) Union Semiconductor, Inc. – 1.0A, 1.5MHz, Synchronous Step-Down DC-DC Converter

UM3510
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 4.7µF 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 ∆V_OUT is approximately:
Layout Guidance
When laying out the PC board, the following suggestions should be taken to ensure proper
operation of the UM3510.
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. Put enough multiply-layer pads when they need
to change the trace layer.
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.02 Dec.2011
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