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AAT1153

2A Step-Down Converter

PRODUCT DATASHEET

1153.2008.02.1.2

www .analogictech.com

AAT1153

2A Step-Down Converter

PRODUCT DATASHEET

1153.2008.02.1.2

www .analogictech.com

Step-Down Converter Design Example

Specifications

VO = 1.8V @ 2A

VIN = 2.7V to 4.2V (3.6V nominal)

fS = 1.2MHz

Transient droop = 200mV

∆VO = 50mV

1.8V Output Inductor

VOUT · (VIN(MAX) - VOUT)

VIN(MAX) ⋅ ΔIL ⋅ fOSC

1.8 · (4.2 - 1.8)

4.2 ⋅ 0.6 · 1.2 · 106

L =

= 1.4µH

ΔIL = 30% ⋅ IO = 0.3 · 2 = 600mA

For Sumida 2.2μH inductor (CDRH2D14) with DCR 75mΩ, the ∆IL should be:

VIN

0.395

ΔIL =

⋅ 1 -

· T = 395mA

IPKL = IO + ΔI

L = 2 +

= 2.2A

PL = IO2 ⋅ DCR = 22 ⋅ 0.0287 = 114.8mW

⎛

⎝

⎞

⎠

1.8V Output Capacitor

3 · ΔILOAD

VDROOP · fS

3 · 1.2

0.2 · 1.2 · 106

COUT =

= 25µF; use 22µF

ESR ≤

= 0.13Ω

ΔVO

ΔIL

0.05

0.395

Select a 22μF, 10mΩ ESR ceramic capacitor to meet the ripple 50mV requirement.

VOUT · (VIN - VOUT)

VIN · fOSC · L

8 · fOSC · COUT

ΔVOUT ≤

· ESR +

⎛

⎝

⎞

⎠

1.8 · (4.2 - 1.8)

4.2 · 1.2 · 106 · 2.2 · 10-6

8 · 1.2 · 106 · 22 · 10-6

· 0.01 +

= 5.7mV

⎛

⎝

⎞

⎠

IRMS =

ΔI

L ·0.289 = 0.395 · 0.289 = 114mArms

PCOUT = ESR · IRMS2 = 0.01 · 12 = 10mW

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