ADP2441ACPZ-R7 datasheet(24/32 Pages) AD

24 / 32 page

ADP2441

Data Sheet

Rev. A | Page 24 of 32

Output Capacitor Selection

Select the output capacitor by using Equation 12 and Equation 13:

)

(

)

(

ESR

RIPPLE

MIN

OUT















Equation 12 is based on the output voltage ripple (ΔVRIPPLE),

which is 1% of the output voltage.





















DROOP

STEP

OUT

MIN

OUT

)

(

)

(

Equation 13 calculates the capacitor selection based on the

transient load performance requirement of 2%. Perform these

calculations, and then use the equation that yields the larger

capacitor size to select a capacitor.

In this example, the values listed in Table 12 are substituted for

the variables in Equation 12 and Equation 13.

Table 12. Requirements

Parameter

Test Conditions/Comments

Value

Ripple Current

Fixed at 0.3 A for the ADP2441

0.3 A

Voltage Ripple

1% of VOUT

50 mV

Voltage Droop Due

to Load Transient

2% of VOUT

100 mV

ESR

5 mΩ

fSW

700 kHz

The calculation based on the output voltage ripple (see

Equation 12) dictates that the minimum output capacitance is

μF

)

mΩ

(

kHz

700

)

(











MIN

OUT

whereas the calculation based on the transient load (see

Equation 13) dictates that the minimum output capacitance is

kHz

700

)

(









MIN

OUT

To meet both requirements, use the value determined by the

latter equation. As shown in Figure 57, capacitance degrades

with dc bias; therefore, choose a capacitor that is 1.5 times the

calculated value.

COUT = 1.5 × 22 μF = 32 μF

Compensation Selection

Calculate the compensation component values for the feedback

loop by using the following equations:

REF

OUT

CROSSOVER

COMP









COMP

ZERO

COMP









Selecting the crossover frequency to be 1/12 of the switching

frequency and placing the zero frequency at 1/8 of the crossover

frequency ensures that there is enough phase margin in the system.

Table 13. Calculated Parameter Value

Parameter

Test Conditions/Comments

Value

fCROSSOVER

1/12 of fSW

58.3 kHz

fZERO

1/8 of fCROSSOVER

7.3 kHz

VREF

Fixed reference

0.6 V

Transconductance of error

amplifier

250 μA/V

GCS

Current sense gain

2 A/V

COUT

Output capacitor

22 μF

VOUT

Output voltage

5 V

Based on the values listed in Table 13, calculate the compen-

sation value:













121

250

COMP

The closest standard resistor value is 118 kΩ. Therefore,

180

185

118











COMP

SYSTEM CONFIGURATION

Configure the system as follows:

Connect a capacitor of 1 μF between the VCC and PGND

pins and another capacitor of 1 μF between the VCC and

AGND pins. For best performance, use ceramic X5R or

X7R capacitors with a 25 V voltage rating.

Connect a ceramic capacitor of 10 nF with a 50 V voltage

rating between the BST and SW pins.

Connect a resistor between the FREQ and AGND pins as

close as possible to the IC.

If using the power-good feature, connect a pull-up resistor

of 50 kΩ to an external supply of 5 V.

Connect a capacitor of 10 nF between the SS and AGND pins.

If the tracking feature is needed, connect a resistor divider

between the TRK pin and another supply, as shown in

Figure 50.

See Figure 60 for a schematic of this design example and Table 14

for the calculated component values.

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