ADP2386ACPZN-R7 datasheet(19/24 Pages) AD

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Data Sheet

ADP2386

Rev. A | Page 19 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:

COUT_RIPPLE =

RIPPLE

OUT

∆

RESR =

RIPPLE

OUT

∆

This calculation results in COUT_RIPPLE = 11.4 μF, and RESR = 18 mΩ.

To meet the ±5% overshoot and undershoot transient

requirements, use the following equations to calculate the

capacitance:

COUT_OV =

)

(

OUT

STEP

−

∆

COUT_UV =

OUT

STEP

)

(

∆

−

∆

where:

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

∆ISTEP = 4 A is the load transient step.

∆VOUT_OV = 5% VOUT is the overshoot voltage.

∆VOUT_UV = 5% VOUT is the undershoot voltage.

This calculation results in COUT_OV = 63.1 μF, and COUT_UV = 24.5 μF.

According to the calculation, the output capacitance must be

greater than 63 μF, and the ESR of the output capacitor must be

smaller than 18 mΩ. It is recommended that one 100 μF/X5R/

6.3 V ceramic capacitor and one 47 μF/X5R/6.3 V ceramic

capacitor be used, such as the GRM32ER60J107ME20 and

GRM32ER60J476ME20 from Murata, with an ESR of 2 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 100 µF and 47 µF ceramic output capacitors have a derated

value of 62 µF and 32 µF.

RC = 2

3.3V

μF 60kHz

0.6 V

480

μs 8.7 A/ V

× ×

××

= 46.7 kΩ

CC = (0.55

0.002

)

μF

46.7 k

Ω+

Ω ×

= 1111 pF

CCP = 0.002

μF

46.7 k

Ω×

= 4.0 pF

Choose standard components, as follows: RC = 44.2 kΩ,

CC = 1200 pF, and CCP = 4.7 pF.

Figure 34 shows the bode plot at 6 A. The cross frequency is

58 kHz, and the phase margin is 61°.

10k

100k

FREQUENCY (Hz)

–12

–24

–36

–48

–60

180

144

108

–36

–72

–108

–144

–180

Figure 34. Bode Plot at 6 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.

CSS =

μA

EXT

= 21.3 nF

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

INPUT CAPACITOR SELECTION

Place a minimum 10 μF ceramic capacitor near the PVIN pin.

In this application, it is recommended that one 10 μF, X5R, 25 V

ceramic capacitor be used.

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