Datasheet

VIN=3 6V-

TPS54218

www.ti.com

SLVS974B –SEPTEMBER 2009–REVISED JULY 2013

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 HPA511 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 to 2A load step ΔV

OUT

= 3%

Maximum Output Current 2 A

Input Voltage 3.3 V nom. 3 V to 6 V

Output Voltage Ripple < 30 mV

Start Input Voltage (rising VIN) 3.1 V

Stop Input Voltage (falling VIN) 2.8 V

Switching Frequency (Fsw) 1000 kHz

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 200 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 5, R4 is calculated to be 180 kΩ. A standard 1% 182 kΩ value was

chosen in the design.

Figure 34. High Frequency, 1.8 V Output Power Supply Design with Adjusted UVLO

OUTPUT INDUCTOR SELECTION

The inductor selected works for the entire TPS54218 input voltage range. To calculate the value of the output

inductor, use Equation 18. K

IND

is a coefficient that represents the amount of inductor ripple current relative to the

maximum output current. The inductor ripple current is filtered by the output capacitor. Therefore, choosing high

inductor ripple currents impacts the selection of the output capacitor since the output capacitor must have a

ripple current rating equal to or greater than the inductor ripple current. In general, the inductor ripple value is at

the discretion of the designer; however, K

IND

is normally from 0.1 to 0.3 for the majority of applications.

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