ADP2441ACPZ-R2 datasheet(19/32 Pages) AD

19 / 32 page

Data Sheet

ADP2441

Rev. A | Page 19 of 32

SOFT START

The soft start function limits the input inrush current and

prevents output overshoot at startup. The soft start time is

programmed by connecting a small ceramic capacitor between

the SS/TRK and AGND pins, with the value of this capacitor

defining the soft start time, tSS, as follows:

REF



(5)

where:

VREF is the internal reference voltage and equals 0.6 V.

ISS is the soft start current and equals 1 μA.

CSS is the soft start capacitor value.

Table 7. Soft Start Time Selection

Soft Start Capacitor (nF)

Soft Start Time (ms)

Alternatively, the user can float the SS/TRK pin and use the

internal soft start time of 2 ms.

EXTERNAL COMPONENTS SELECTION

Input Capacitor Selection

The input current to a buck regulator is pulsating in nature. The

current is zero when the high-side switch is off and is approxi-

mately equal to the load current when the switch is on. Because

switching occurs at reasonably high frequencies (300 kHz to

1 MHz), the input bypass capacitor usually supplies most of

the high frequency current (ripple current), allowing the input

power source to supply only the average (dc) current. The input

capacitor needs a sufficient ripple current rating to handle the

input ripple and needs an ESR that is low enough to mitigate the

input voltage ripple. In many cases, different types of capacitors

are placed in parallel to minimize the effective ESR and ESL.

The minimum input capacitance required for a particular load is

ESR

OUT

MIN

)

(

)

(









(6)

where:

VPP is the desired input ripple voltage.

RESR is the equivalent series resistance of the capacitor.

IOUT is the maximum load current.

It is recommended to use a ceramic bypass capacitor because

the ESR associated with this type of capacitor is near zero,

simplifying the equation to

OUT

MIN









)

(

(7)

In addition, it is recommended to use a ceramic capacitor with a

voltage rating that is 1.5 times the input voltage with X5R and X7R

dielectrics. Using Y5V and Z5U dielectrics is not recommended

due to their poor temperature and dc bias characteristics. Table 10

shows a list of recommended MLCC capacitors from Murata

and Taiyo Yuden.

For large step load transients, add more bulk capacitance by, for

example, using electrolytic or polymer capacitors. Make sure

that the ripple current rating of the bulk capacitor exceeds the

minimum input ripple current of a particular design.

Inductor Selection

The high switching frequency of the ADP2441 allows for

minimal output voltage ripple even when small inductors are used.

Selecting the size of the inductor involves considering the trade-off

between efficiency and transient response. A smaller inductor

results in larger inductor current ripple, which provides excellent

transient response but degrades efficiency. Due to the high

switching frequency of the ADP2441, using shielded ferrite core

inductors is recommended because of their low core losses and

low EMI.

The inductor ripple current also affects the stability of the loop

because the ADP2441 uses the emulated peak current mode

architecture. In the traditional approach of slope compensation,

the user sets the inductor ripple current and then sets the slope

compensation using an external ramp resistor. In most cases, the

inductor ripple current is typically set to be 1/3 of the maximum

load current for optimal transient response and efficiency. The

ADP2441 has internal slope compensation, which assumes that

the inductor ripple current is set to 0.3 A (30% of the maximum

load of 1 A), eliminating the need for an external ramp resistor.

For the ADP2441, choose an inductor such that the peak-to-

peak ripple current of the inductor is between 0.2 A and 0.5 A

for stable operation.

Therefore, calculate the inductor value as follows:

OUT











)

(

(8)

0.2 A ≤ ΔIL ≤ 0.5 A

OUT















)

(

)

(

OUT

IDEAL









)

(

(9)

where:

VIN is the input voltage.

VOUT is the desired output voltage.

fSW is the regulator switching frequency.

For applications with a wide input (VIN) range, choose the

inductor based on the geometric mean of the input voltage

extremes.

MIN

MAX

GEOMETRIC

)

(





where:

VIN_MAX is the maximum input voltage.

VIN_MIN is the minimum input voltage.

ADP2441ACPZ-R2 数据表(PDF) 19 Page - Analog Devices

ADP2441ACPZ-R2 数据表(HTML) 19 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

数据表下载

链接网址

ADP2441ACPZ-R2 数据表(PDF) 19 Page - Analog Devices

ADP2441ACPZ-R2 数据表(HTML) 19 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

数据表 下载

链接网址

数据表下载