DR73-4R7-R datasheet(16/19 Pages) SKYWORKS

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AAT1162

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

DATA SHEET

Design Example

Specifications

VOUT

5V @ 1.5A, Pulsed Load ILOAD = 1.5A

VIN

12V nominal

FOSC

800kHz

TAMB

85°C in TDFN34-16 Package

Output Inductor

VOUT

3.3

L =

· 3.8µH = 5.75µH; use 4.7µH (see Table 2)

ΔIL = 0.32 · ILOAD = 480mA

For Cooper Bussman inductor DR73-4R7-R 4.7μH DCR = 29.7mW max.

VOUT

VO1

ΔI1 =

⋅ 1 -

= 480mA

L1 ⋅ FOSC

VIN

4.7µH ⋅ 800kHz

12V

IPK1 = ILOAD + ΔI

1 = 1.5A + 0.480A = 1.98A

PL1 = ILOAD2 ⋅ DCR = 3A2 ⋅ 13mΩ = 117mW

⎛

⎝

⎞

⎠

⎛

⎝

⎞

⎠

Output Capacitor

VDROOP = 0.2V

5V · (12V - 5V)

4.7µH · 800kHz · 12V

RMS(MAX)

L · FOSC · VIN(MAX)

3 · ΔILOAD

VDROOP · FOSC

3 · 1.5A

0.2V · 800kHz

COUT =

= 28µF; use 22µF

= 139mArms

(VOUT) · (VIN(MAX) - VOUT) =

Pesr = esr · IRMS2 = 5mΩ · (277mA)2 = 384µW

Input Capacitor

Input Ripple VPP = 50mV

CIN =

= 11µF; use 10µF

⎛⎞

- ESR ·

4 · FOSC

⎝⎠

VPP

ILOAD

⎛⎞

- 5mΩ ·

4 · 800kHz

⎝⎠

50mV

1.5A

ILOAD

RMS(MAX)

P = esr · IRMS2 = 5mΩ · (0.75A)2 = 2.81mW

= 0.75Arms

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