TPS54386PWPR datasheet(18/52 Pages) TI

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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

TPS54383,, TPS54386

SLUS774B – AUGUST 2007 – REVISED OCTOBER 2007

Figure 23. Small Signal Equivalent Block Diagram

The following figures plot the TPS5438x 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 20 kHz and 60 kHz. See the following sections for further details.

GAIN AND PHASE

FREQUENCY

Figure 24. TPS54383 at 200-mApp Ripple Current

Figure 25. TPS54383 at 400-mApp Ripple Current

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