REF

OUT

REF

R5

V

R6 =

V

V

´

-

OUT

REF

R5

V

= V

+1

R6

é

ù

´

ê

ú

ë

û

TPS54233-Q1

www.ti.com

SLUSAZ7A – MARCH 2012 – REVISED MARCH 2012

STEP BY STEP DESIGN PROCEDURE

The following design procedure can be used to select component values for the TPS54233-Q1. Alternately, the

SwitcherPro™Software may be used to generate a complete design. The SwitcherPro™ Software uses an

iterative design procedure and accesses a comprehensive database of components when generating a design.

This section presents a simplified discussion of the design process.

To begin the design process a few parameters must be decided upon. The designer needs to know the following:

•

Input voltage range

•

Output voltage

•

Input ripple voltage

•

Output ripple voltage

•

Output current rating

•

Operating frequency

For this design example, use the following as the input parameters

Table 3. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Input voltage range

8 V to 18 V

Output voltage

3.3 V

Input ripple voltage

300 mV

Output ripple voltage

100 mV

Output current rating

2 A

Operating Frequency

300 kHz

SWITCHING FREQUENCY

The switching frequency for the TPS54233-Q1 is fixed at 300 kHz.

OUTPUT VOLTAGE SET POINT

The output voltage of the TPS54233-Q1 is externally adjustable using a resistor divider network. In the

application circuit of Figure 12, this divider network is comprised of R5 and R6. The relationship of the output

voltage to the resistor divider is given by Equation 4 and Equation 5:

(4)

(5)

Choose R5 to be approximately 10 k

Ω. Slightly increasing or decreasing R5 can result in closer output voltage

matching when using standard value resistors. In this design, R5 = 10.2 k

Ω and R6 = 3.24 kΩ, resulting in a

3.31 V output voltage.

INPUT CAPACITORS

The TPS54233-Q1 requires an input decoupling capacitor and depending on the application, a bulk input

capacitor. The typical recommended value for the decoupling capacitor is 10

μF. A high-quality ceramic type X5R

or X7R is recommended. The voltage rating should be greater than the maximum input voltage. A smaller value

may be used as long as all other requirements are met; however 10

μF has been shown to work well in a wide

variety of circuits. Additionally, some bulk capacitance may be needed, especially if the TPS54233-Q1 circuit is

not located within about 2 inches from the input voltage source. The value for this capacitor is not critical but

should be rated to handle the maximum input voltage including ripple voltage, and should filter the output so that

input ripple voltage is acceptable. For this design two 4.7

μF capacitors are used for the input decoupling

capacitor. They are X7R dielectric rated for 50 V. The equivalent series resistance (ESR) is approximately 2 m

Ω,

and the current rating is 3 A. Additionally, a small 0.01

μF capacitor is included for high frequency filtering.

This input ripple voltage can be approximated by Equation 6

Copyright © 2012, Texas Instruments Incorporated

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