ADP2165ACPZ-1.2-R7 datasheet(16/23 Pages) AD

16 / 23 page

ADP2165/ADP2166

Data Sheet

Rev. B | Page 16 of 23

The ESR and the value of the capacitance determine the output

ripple. Use the following equation to select a capacitor that can

meet the output ripple requirements:

COUT_RIPPLE =

RIPPLE

OUT

∆

RESR =

RIPPLE

OUT

∆

where:

ΔVOUT_RIPPLE is the allowable output ripple voltage.

RESR is the equivalent series resistance of the output capacitor

in ohms (Ω).

Select the largest output capacitance given by COUT_UV, COUT_OV,

and COUT_RIPPLE to meet both the load transient and the output

ripple performance.

The selected output capacitor voltage rating must be greater

than the output voltage. The rms current rating of the output

capacitor must be larger than the value calculated by

OUT_RMS

∆

COMPENSATION DESIGN

For peak current mode control, the power stage can be simplified

as a voltage controlled current source supplying current to the

output capacitor and load resistor. It is composed of one domain

pole and a zero that is contributed by the output capacitor ESR.

The control to output transfer function is based on the following:

GVD (S) =

)

(

)

(

COMP

OUT

= AVI × R ×

fZ =

OUT

ESR

fP =

OUT

ESR

)

(

where:

AVI = 10 A/V.

R is the load resistance.

COUT is the output capacitance.

RESR is the equivalent series resistance of the output capacitor.

The ADP2165/ADP2166 use a transconductance amplifier for the

error amplifier, which compensates for the system loop. Figure 30

shows the simplified, peak current mode control, small signal circuit.

RESR

–

CCP

COUT

RTOP

RBOT

–

AVI

VOUT

VCOMP

VOUT

Figure 30. Simplified Peak Current Mode Control, Small Signal Circuit

The compensation components, RC and CC, contribute a zero,

and the optional CCP and RC contribute an optional pole.

The loop gain transfer equation is as follows:

TV (S) =

−

TOP

BOT

()

)

CCCP

××

×+

The following design guideline shows how to select the RC, CC,

and CCP compensation components for the ceramic output

capacitor applications:

1. Determine the cross frequency, fC. Generally, fC is between

fSW/12 and fSW/6.

2. Calculate RC by using the following equation:

OUT

3. Place the compensation zero at the domain pole, fP; then

determine CC by using the following equation:

OUT

ESR

)

(

4. CCP is optional. It can be used to cancel the zero caused by

the ESR of the output capacitor.

OUT

ESR

The fixed output version IC must consider the feedforward

capacitance of feedback resistor (RTOP) to calculate CCP.

The total internal feedback resistance is 1 MΩ.

First, place the compensation pole at the minimum value

between the domain pole, fP, and

)

(

2π

BOT

TOP

2π

Then, determine CCP by

(

)

(

)

min

−

where CF = 8.14 pF.

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