LC

OUT

OUT

L

C

1

¦ =

2p

Z

R C

1

1

¦ =

2p 3 6

Z

R C

2

1

¦ =

2p 1 8

P

R C

1

1

¦ =

2p 5 8

P

R C

2

1

¦ =

2p 3 7

INT

R C

1

¦

=

2p 1 6

-

CO

INT

0.74

10

´ ¦

¦

=

2

INT

C

R

1

6 =

2p 1¦

LC

R

C

1

1 =

2p 6¦

TPS54110

www.ti.com

SLVS500C

– DECEMBER 2003 – REVISED FEBRUARY 2011

There are a number of different ways to design a compensation network. This procedure outlines a relatively

simple procedure that produces good results with most output filter combinations. Use the SWIFT Designer

Software for designs with unusually high closed-loop crossover frequencies; with low-value, low-ESR output

capacitors such as ceramics; or if you are unsure about the design procedure.

A number of considerations apply when designing compensation networks for the TPS54110. The compensated

error-amplifier gain must not be limited by the open-loop amplifier gain characteristics and must not produce

excessive gain at the switching frequency. Also, the closed-loop crossover frequency must be set less than one

fifth of the switching frequency, and the phase margin at crossover must be greater than 45 degrees. The

general procedure outlined here meets these requirements without going into great detail about the theory of

loop compensation.

First, calculate the output filter LC corner frequency using Equation 10:

(10)

For the design example,

Also, keep the crossover frequency below 100 kHz, as the error amplifier may not provide the desired gain at

higher frequencies. The 60-kHz crossover frequency chosen for this design provides comparatively wide loop

bandwidth while still allowing adequate phase boost to ensure stability.

Next, the values for the compensation components that set the poles and zeros of the compensation network are

calculated. Assuming an R1 value

> than R5 and a C6 value > C7, the pole and zero locations are given by

Equation 11 through Equation 14:

(11)

(12)

(13)

(14)

Additionally there is a pole at the origin, which has unity gain at a frequency:

(15)

This pole is used to set the overall gain of the compensated error amplifier and determines the closed loop

crossover frequency. Since R1 is given as 10 k

Ω and the crossover frequency is selected as 60 kHz, the desired

(16)

And the value for C6 is given by Equation 17:

(17)

Since C6 is calculated to be 2900 pF, and the location of the integrator crossover frequency is important in

setting the overall loop crossover, adjust the value of R1 so that C6 is a standard value of 2700 pF, using

Equation 18:

(18)

The value for R1 is 10.7 K

Ω

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