MIC45404 datasheet(24/32 Pages) MICROCHIP

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MIC45404

DS20005478A-page 24

 2015 Microchip Technology Inc.

For example, setting the compensator pole at 5 fXO will

limit its associated phase loss at the crossover

frequency to about 11°. Placement at even higher

frequencies, N × fXO (N > 5), will reduce phase loss

even further at the expense of less noise/ripple attenu-

ation at the switching frequency. Some attenuation of

the switching frequency noise/ripple is achieved as

long as N × fXO <fS.

For the polarized output capacitor, compensator pole

placement at the ESR zero frequency is achieved, as

shown in Equation 5-20:

EQUATION 5-20:

For the ceramic output capacitor, compensator pole

placement at N × fXO (N 5, N × fXO < fS) is achieved,

as detailed in Equation 5-21:

EQUATION 5-21:

The MIC45404 already provides an internal CC2 capac-

itor of 47 pF. Therefore, the external capacitance,

CC2_EXT, that should be added is given by

Equation 5-22:

EQUATION 5-22:

If the result, CC2 – 47 pF, yields to zero or to a negative

number, no additional external capacitance is needed

for CC2.

5.9

Output Voltage Soft Start Rate

The MIC45404 features an internal analog soft start,

such that the output voltage can be smoothly increased

to the target regulation voltage. The soft start rate given

in Section 1.0 “Electrical Characteristics” is referred

to the error amplifier reference, and therefore, the

effective soft start rate value, seen at the output of the

module, has to be scaled according to the internal feed-

back divider attenuation values listed in Table 5-5. To

calculate the effective output voltage soft start slew

rate, SS_SROUT, based on the particular output voltage

setting and the reference soft start slew rate, SS_SR,

use the following formula:

EQUATION 5-23:

For the value of A, see the right column of Table 5-5.

ESR



------------------------

----------

–

-----------------------------------------

C 2

 R



----------

–



----------------------------------------------------------------

C2_EXT

max C

47 pF, 0 pF

–



SS_SR

OUT

SS_SR



Where:

A = Amplification

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