11

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

201998B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013

AAT1162

12V, 1.5A Step-Down DC/DC Converter

DATA SHEET

The external resistors set the output voltage according

to the following equation:

⎛⎞

⎝⎠

R1

R2

or

⎛⎞

⎝⎠

R1 =

Table 1 shows the resistor selection for different output

voltage settings.

R2 = 5.9(kΩ)

R1 (kΩ)

R2 = 59(kΩ)

R1 (kΩ)

0.8

1.96

19.6

0.9

2.94

29.4

1.0

3.92

39.2

1.1

4.99

49.9

1.2

5.90

59.0

1.3

6.81

68.1

1.4

7.87

78.7

1.5

8.87

88.7

1.8

11.8

118

1.85

12.4

124

2.0

13.7

137

2.5

18.7

187

3.3

26.7

267

5.0

43.2

432

Table 1: Resistor Selection for Different Output

Voltage Settings. Standard 1% Resistors are

Substituted for Calculated Values.

Inductor Selection

For most designs, the AAT1162 operates with inductors

of 2μH to 4.7μH. Low inductance values are physically

smaller, but require faster switching, which results in

some efficiency loss. The inductor value can be derived

from the following equation:

3.3

L1 =

· 3.8µH

tors lower ripple current and small value inductors result

in high ripple currents. Choose inductor ripple current

approximately 32% of the maximum load current 1.5A,

minimum recommended inductor is 3.8μH. For 3.3V and

below, use a 2 to 3.8μH inductor. For optimum voltage-

positioning load transients, choose an inductor with DC

series resistance in the 15mΩ to 20mΩ range.

For

higher efficiency at heavy loads (above 1A), or minimal

load regulation (but some transient overshoot), the

resistance should be kept below 18mΩ. The DC current

rating of the inductor should be at least equal to the

maximum load current plus half the ripple current to

prevent core saturation (1.5A + 280mA). Table 2 lists

some typical surface mount inductors that meet target

applications for the AAT1162.

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 satura-

tion 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 losses 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. For example, the 4.7μH WE-TPC series

inductor selected from Wurth has an 38mΩ DCR and a

2.4ADC current rating. At full load, the inductor DC loss

is 85mW which gives only a 1.1% loss in efficiency for a

1.5A, 5V output.

Input Capacitor Selection

The input capacitor reduces the surge current drawn

from the input and switching noise from the device. The

input capacitor impedance at the switching frequency

shall be less than the input source impedance to prevent

high frequency switching current passing to the input. A

low ESR input capacitor sized for maximum RMS current

must be used. Ceramic capacitors with X5R or X7R

dielectrics are highly recommended because of their low

ESR and small temperature coefficients. A 10μF ceramic

capacitor is sufficient for most applications.