7.2.1 Design Requirements

The following table shows the design parameters for this application.

Table 7-1. Design Parameters

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNIT

VIN

Input voltage

5.5

12

18

V

VOUT

Output voltage

5

V

IOUT

Output current rating

2

A

VIN(ripple)

Input ripple voltage

400

mV

VOUT(ripple)

Output ripple voltage

30

mV

FSW

Switching frequency

RT = floating

1000

kHz

tSS

Soft-start time

CSS = 33nF

3.6

mS

TA

Ambient temperature

25

°C

7.2.2 Detailed Design Procedure

7.2.2.1 Custom Design With WEBENCH® Tools

Create a custom design with the TPSM843521 using the WEBENCH® Power Designer.

1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.

2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.

3. Compare the generated design with other possible solutions from Texas Instruments.

The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

• Run electrical simulations to see important waveforms and circuit performance

• Run thermal simulations to understand board thermal performance

• Export customized schematic and layout into popular CAD formats

• Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

7.2.2.2 Output Voltage Resistors Selection

The output voltage is set with a resistor divider from the output node to the FB pin. TI recommends using 1%

tolerance or better divider resistors. Referring to the application schematic of Figure 7-1, start with 30kΩ for R5

and use Equation 15 to calculate R4 = 220kΩ. To improve efficiency at light loads, consider using larger value

resistors. If the values are too high, the converter is more susceptible to noise and voltage errors from the FB

input leakage current are noticeable.

R4=VOUT−VREF

VREF ×R5

(15)

7.2.2.3 Choosing Switching Frequency

The choice of switching frequency is a compromise between conversion efficiency and overall design size.

Higher switching frequency allows the use of smaller inductors and output capacitors, and hence, a more

compact design. However, lower switching frequency implies reduced switching losses and usually results in

higher system efficiency, so the 1000kHz switching frequency was chosen for this example, use 0Ω for R6.

Please note the switching frequency is also limited by the following as mentioned in Section 6.3.10:

• Minimum on time of the integrated power switch

• Input voltage

• Output voltage

• Frequency shift limitation

TPSM843521

SLUSG64 – APRIL 2025

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