1

2

P

OUT

OUT

F

L

C

p

=

´

V

=

OUT

R2

−

)

U1

TPS54526PWP

TPS54526

www.ti.com

SLVSB84 – MAY 2012

DESIGN GUIDE

Step By Step Design Procedure

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

•

Input voltage range

•

Output voltage

•

Output current

•

Output voltage ripple

•

Input voltage ripple

Figure 16. 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 very light loads consider using larger value resistors, too high of resistance will be more

susceptible to noise and voltage errors from the VFB input current will be more noticeable

(3)

Output Filter Selection

The output filter used with the TPS54526 is an LC circuit. This LC filter has double pole at:

(4)

At low frequencies, the overall loop gain is set by the output set-point resistor divider network and the internal

gain of the TPS54526. The low frequency phase is 180 degrees. At the output filter pole frequency, the gain rolls

off at a -40 dB per decade rate and the phase drops rapidly. D-CAP2™ introduces a high frequency zero that

reduces the gain roll off to –20 dB per decade and increases the phase to 90 degrees one decade above the

zero frequency. The inductor and capacitor selected for the output filter must be selected so that the double pole

of Equation 4 is located below the high frequency zero but close enough that the phase boost provided be the

high frequency zero provides adequate phase margin for a stable circuit. To meet this requirement use the

values recommended in Table 1

Copyright © 2012, Texas Instruments Incorporated

13

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