Datasheet

TPS54478

www.ti.com

SLVSAS2 –JUNE 2011

APPLICATION INFORMATION

DESIGN GUIDE – STEP-BY-STEP DESIGN PROCEDURE

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

This design is available as the TPS54478EVM-037 (PWR037) 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, we start with the following known parameters:

Output Voltage 1.8 V

Transient Response 1 A to 3.0 A load step ΔVout = 3%

Maximum Output Current 4 A

Input Voltage 3 V to 6V, 5 V nominal

Output Voltage Ripple < 30 mV p-p

Switching Frequency (Fsw) 1000 kHz

The schematic diagram for this design example is shown in Figure 35. The component reference designators of

this schematic are used for the equations in APPLICATION INFORMATION.

SELECTING THE SWITCHING FREQUENCY

The first step is to decide on a switching frequency for the regulator. Typically, you want to choose the highest

switching frequency possible since this produces the smallest solution size. The high switching frequency allows

for lower valued inductors and smaller output capacitors compared to a power supply that switches at a lower

frequency. However, the highest switching frequency causes extra switching losses, which hurt the converter’s

performance. The converter is capable of running from 300 kHz to 2 MHz. Unless a small solution size is an

ultimate goal, a moderate switching frequency of 1MHz is selected to achieve both a small solution size and a

high efficiency operation. Using Equation 7, R4 is calculated to be 35.4 kΩ. A standard 1% 35.7 kΩ value was

chosen in the design.