SLMA002 datasheet(18/55 Pages) TI1

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VREF

VIN

VOUT

Compensation

Network

Modulator

Filter

Current

Feedback

Network

Inductor-Capacitor (L-C) Selection

100

1 M

1 k

100 k

10 k

-90

135

180

-45

270

225

Duty Cycle %

Gain

Phase

-20

100

1 M

1 k

100 k

10 k

-90

135

180

-45

270

225

f - Frequency -Hz

100

-20

100

Duty Cycle %

Gain

Phase

TPS54283,, TPS54286

SLUS749C – JULY 2007 – REVISED OCTOBER 2007

Figure 22. Small Signal Equivalent Block Diagram

The following figures plot the TPS5428x Output-to-Vc gain and phase versus frequency for various duty cycles

(10%, 30%, 50%, 70%, 90%) at three (200 mA, 400 mA, 600 mA) peak-to-peak ripple current levels. The loop

response curve selected to compensate the loop is based on the duty cycle of the application and the ripple

current in the inductor. Once the curve has been selected and the inductor value has been calculated, the output

capacitor is found by calculating the L-C resonant frequency required to compensate the feedback loop. A brief

example follows the curves.

Note that the internal error amplifier compensation is optimized for output capacitors with an ESR zero frequency

between 20kHz and 60kHz. See the following sections for further details.

GAIN AND PHASE

FREQUENCY

Figure 23. TPS54283 at 200-mAp-p Ripple Current

Figure 24. TPS54283 at 400-mAp-p Ripple Current

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Product Folder Link(s): TPS54283 TPS54286

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