ADP2443ACPZN-R7 datasheet(21/25 Pages) AD

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ADP2443

Data Sheet

Rev. 0 | Page 20 of 24

OUTPUT CAPACITOR SELECTION

The output capacitor is required to meet both the output voltage

ripple and load transient response requirements.

To meet the output voltage ripple requirement, use the following

equation to calculate the ESR and capacitance value of the output

capacitor:

RIPPLE

OUT

RIPPLE

OUT

∆

RIPPLE

OUT

ESR

∆

This calculation results in COUT_RIPPLE = 4.04 μF, and RESR = 51.5 mΩ.

To meet the ±5% overshoot and undershoot transient

requirements, use the following equations to calculate the

capacitance:

)

(

OUT

STEP

OUT

−

∆

where:

KOV = KUV = 2 are the coefficients for estimation purposes.

∆ISTEP = 2 A is the load transient step.

∆VOUT_OV = 5% VOUT is the overshoot voltage.

OUT

STEP

OUT

)

(

∆

−

∆

where ∆VOUT_UV = 5% VOUT is the undershoot voltage.

This calculation results in COUT_OV = 21.2 μF, and COUT_UV = 5.7 μF.

According to the calculation, the output capacitance must be

greater than 21.2 μF, and the ESR of the output capacitor must be

smaller than 51.5 mΩ. It is recommended that one 47 μF/X5R/16 V

ceramic capacitor be used, such as the GRM32ER61C476KE15K

from Murata, with an ESR of 2 mΩ.

SLOPE COMPENSATION SETTING

The ramp resistor, RRAMP, determines the slope compensation.

Use the following equation to calculate the RRAMP value:

MΩ

μH

= L

RRAMP

Choose a standard component value, as follows: RRAMP = 1.5 MΩ.

COMPENSATION COMPONENTS

For better load transient and stability performance, set the cross

frequency, fC, to fSW/10. In this case, fSW is running at 600 kHz;

therefore, the fC is set to 60 kHz.

The 47 µF ceramic output capacitor has a derated value of 32 µF.

kΩ

A/V

µs

515

0.6

kHz

µF

2739

kΩ

19.5

µF

0.002

1.667

kΩ

19.5

µF

0.002

Choose standard components, as follows: RC = 20 kΩ,

CC = 2700 pF, and CCP = 3.3 pF.

Figure 40 shows the Bode plot at a 3 A load current. The cross

frequency is 59 kHz, and the phase margin is 66°.

–60

–24

–36

–48

–12

180

–180

–72

144

–108

108

–144

–36

10k

100k

FREQUENCY (Hz)

PHASE

MAGNITUDE

Figure 40. Bode Plot at 3 A

SOFT START TIME PROGRAM

The soft start feature allows the output voltage to ramp up in a

controlled manner, eliminating output voltage overshoot during

soft start and limiting the inrush current. Set the soft start time

to 4 ms.

0.6

µA

0.6

EXT

Choose a standard component value, as follows: CSS = 22 nF.

INPUT CAPACITOR SELECTION

A minimum 10 μF ceramic capacitor must be placed near the

PVIN pin. In this application, it is recommended that one 10 μF,

X5R, 50 V ceramic capacitor be used.

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