AAT2510 datasheet(10/20 Pages) ANALOGICTECH

10 / 20 page

AAT2510

Dual 400mA, 1MHz Step-Down DC-DC Converter

2510.2005.08.1.5

Applications Information

Inductor Selection

The step-down converter uses peak current mode

control with slope compensation to maintain stabil-

ity for duty cycles greater than 50%. The output

inductor value must be selected so the inductor

current down slope meets the internal slope com-

pensation requirements. The internal slope com-

pensation for the adjustable and low-voltage fixed

versions of the AAT2510 is 0.24A/µsec. This

equates to a slope compensation that is 75% of the

inductor current down slope for a 1.5V output and

4.7µH inductor.

This is the internal slope compensation for the

adjustable (0.6V) version or low-voltage fixed ver-

sion. When externally programming the 0.6V ver-

sion to a 2.5V output, the calculated inductance

would be 7.5µH.

In this case, a standard 10µH value is selected.

For high-voltage fixed versions (2.5V and above),

m = 0.48A/µsec. Table 1 displays inductor values

for the AAT2510 fixed and adjustable options.

Manufacturer's specifications list both the inductor

DC current rating, which is a thermal limitation, and

the peak current rating, which is determined by the

saturation characteristics. The inductor should not

show any appreciable saturation under normal load

conditions. Some inductors may meet the peak and

average current ratings yet result in excessive loss-

es due to a high DCR. Always consider the losses

associated with the DCR and its effect on the total

converter efficiency when selecting an inductor.

The 4.7µH CDRH3D16 series inductor selected

from Sumida has a 105m

Ω DCR and a 900mA DC

current rating. At full load, the inductor DC loss is

17mW which gives a 2.8% loss in efficiency for a

400mA 1.5V output.

Input Capacitor

Select a 4.7µF to 10µF X7R or X5R ceramic capac-

itor for the input. To estimate the required input

capacitor size, determine the acceptable input rip-

ple level (V

PP) and solve for C. The calculated

value varies with input voltage and is a maximum

when V

IN is double the output voltage.

This equation provides an estimate for the input

capacitor required for a single channel.

⎛⎞

⋅ 1 -

⎝⎠

IN =

⎛⎞

- ESR

⋅ F

⎝⎠

0.75

⋅ V

L =

≈ 3

⋅ V

= 3

⋅ 2.5V = 7.5µH

0.75V

0.24A/

µsec

0.75

⋅ V

m =

= 0.24

0.75

⋅ 1.5V

4.7

µH

µsec

Table 1: Inductor Values.

Configuration

Output Voltage

Inductor

Slope Compensation

0.6V Adjustable With

0.6V to 2.0V

4.7µH

0.24A/µsec

External Resistive Divider

2.5V

10µH

0.24A/µsec

Fixed Output

0.6V to 2.0V

4.7µH

0.24A/µsec

2.5V to 3.3V

4.7µH

0.48A/µsec

AAT2510 датащи(PDF) 10 Page - Advanced Analogic Technologies

AAT2510 датащи(HTML) 10 Page - Advanced Analogic Technologies

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

датащи скачать

ссылки URL