F

=

P

OUT

OUT

1

2

L

x C

p

V

= 0.765 x

OUT

R1

1 +

R2

æ

ö÷

ç

÷

ç

÷÷

çè

ø

C1

L1

R2

22.1kΩ

R1

8.25kΩ

C5

0.47μF

EN

VFB

VREG5

SS

VIN

4.5 to 23V

10μF

C2

C3

10μF

0.1μF

7

5

6

8

VIN

VBST

SW

GND

2

1

3

4

VOUT

C6

8200pF

PwrPAD

2.2μH

1

C4

U1

TPS54239DDA

9

R3

10.0kΩ

C7 0.1μF

C8

22μF

VOUT

C9

22μF

VIN

1

Not Installed

EN

VOUT

1.05V 2A

C10

1

TPS54239

www.ti.com

SLVSBT0 – JANUARY 2013

DESIGN GUIDE

Step-By-Step Design Procedure

To begin the design process, the user must know a few application parameters:

•

Input voltage range

•

Output voltage

•

Output current

•

Output voltage ripple

•

Input voltage ripple

Figure 14. Shows the schematic diagram for this design example.

Output Voltage Resistors Selection

The output voltage is set with a resistor divider from the output node to the VFB pin. It is recommended to use

To improve efficiency at light loads consider using larger value resistors, high resistance is more susceptible to

noise, and the voltage errors from the VFB input current are more noticeable.

(2)

Output Filter Selection

The output filter used with the TPS54239 is an LC circuit. This LC filter has double pole at:

(3)

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Product Folder Links: TPS54239