ADP2165ACPZ-3.3-R7 datasheet(18/23 Pages) AD

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ADP2165/ADP2166

Data Sheet

Rev. B | Page 18 of 23

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 = 14 µF and RESR = 7.4 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

PVIN

STEP

)

(

∆

−

∆

where:

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

∆ISTEP = 4 A, the load transient step.

∆VOUT_OV = 5% × VOUT, the overshoot voltage.

∆VOUT_UV = 5% × VOUT, the undershoot voltage.

This calculation results in COUT_OV = 100 µF and COUT_UV = 33 µF.

According to the calculation, the output capacitance must be

greater than 100 µF, and the ESR of the output capacitor must be

smaller than 7.4 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 1200 kHz;

therefore, the fC is set to 120 kHz.

The 100 µF and 47 µF ceramic output capacitors have a derated

value of 62 µF and 32 µF.

RC =

A/V

μs

500

0.6

kHz

120

μF

1.2

= 28.35 kΩ

CC =

kΩ

28.35

μF

Ω)

0.002

(0.2

= 669.8 pF

CCP =

kΩ

28.35

μF

0.002 ×

= 6.63 pF

Choose standard components as follows: RC = 27 kΩ, CC = 680 pF,

and CCP = 4.7 pF.

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

= 23.3 nF

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

INPUT CAPACITOR SELECTION

A minimum 22 µF ceramic capacitor must be placed near the

PVIN pin. In this application, it is recommended that one 47 µF,

X5R, 16 V ceramic capacitor be used.

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