TPS54386PWPR datasheet(36/52 Pages) TI

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OUT1

(32)

OUT2

(33)

Compensation Capacitors

fESR(zero)

ESR

´ p ´

(34)

ZERO(desired)

ESR(zero)

(35)

ö æ

÷ ç

ø è

(36)

ESR(zero)

´ p ´

(37)

Input Capacitor Selection

TPS54383,, TPS54386

SLUS774B – AUGUST 2007 – REVISED OCTOBER 2007

• R2 = R9 = 20 kΩ

• V

FB = 0.80 V

• R4= 3.80 kΩ (3.83 kΩ standard value is used)

• R7= 6.40 kΩ (6.34 kΩ standard value is used)

Checking the ESR zero of the output capacitors:

• C = 100 µF

• ESR = 400 mΩ

• ESR(zero) = 3980 Hz

Since the ESR zero of the main output capacitor is less than 20 kHz, an R-C filter is added in parallel with R4

and R7 to compensate for the electrolytic capacitors' ESR and add a zero approximately 40 kHz.

• f

ESR(zero) = 4 kHz

• f

ESR(desired) = 40 kHz

• R4 = 3.83 kΩ

• R5 = 424Ω (422Ω selected)

• R7 = 6.34 kΩ

• R8 = 702Ω (698Ω selected)

• R2 = R9 = 20 kΩ

• R

EQ1 = 3.63 kΩ

• R

EQ2 = 5.51 kΩ

• C8 = 10.9 nF (10 nF selected)

• C15 = 7.22 nF (6800 pF selected)

The TPS54383 datasheet recommends a minimum 10-

µF ceramic input capacitor on each PVDD pin. These

capacitor must be capable of handling the RMS ripple current of the converter. The RMS current in the input

capacitors is estimated by Equation 38.

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