ACE7215C

1.5A 1.5MHz Synchronous Buck Converter

VER 1.1

6

Input Capacitor Selection

Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their

high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications.

Because the ACE7215C

’s control loop does not depend on the output capacitor’s ESR for stable

operation, ceramic capacitors can be used freely to achieve very low output ripple and small circuit size.

However, care must be taken when ceramic capacitors are used at the input and the output. When a

ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a

load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output

and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can

potentially cause a voltage spike at VIN, large enough to damage the part. When choosing the input and

output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best

temperature and voltage characteristics of all the ceramics for a given value and size.

PC Board Layout Checklist

When laying out the printed circuit board, the following checking should be used to ensure proper

operation of the ACE7215C. Check the following in your layout:

1.

The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short,

direct and wide.

2.

Does the (+) plates of Cin connect to Vin as closely as possible? This capacitor provides the AC

current to the internal power MOSFETs.

3.

Keep the switching node, SW, away from the sensitive VOUT node.

4.

Keep the (-) plates of Cin and Cout as close as possible