TPS54326

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SLVSA13A – OCTOBER 2009 – REVISED OCTOBER 2009

DESIGN GUIDE

Step By Step Design Procedure

This example details the design of a switching regulator design using ceramic output capacitors.

This design is available as the HPA540 evaluation module (EVM). A few parameters must be known in order to

start the design process. These parameters are typically determined on the system level. For this example,

start with the following known parameters:

•

Input voltage range = 4.5 - 18 V

•

Output voltage = 1.05 V

•

Output current = 3 A

•

Output voltage ripple = 3% of output voltage, 31.5 mV

Figure 13 shows the schematic diagram for this design example.

Figure 13. Schematic

Output Inductor Selection

The inductance value is selected to provide approximately 30% peak-to-peak ripple current at maximum load.

Larger ripple current increases output ripple voltage, improves S/N ratio and contributes to stable operation.

Smaller ripple currents result in lower output voltage ripple. When using low ESR output capacitors output ripple

voltage is usually low, so larger ripple currents are acceptable. The coefficient Kind represents the percentage of

ripple current. The value of Kind must not be greater than 0.4. Use 0.3 when using low ESR output capacitors.

peak current of Equation 5 and the RMS current of Equation 6.

Copyright © 2009, Texas Instruments Incorporated

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