AAT1153 데이터 시트보기 (PDF) - Advanced Analogic Technologies

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AAT1153

2A Step-Down Converter

Advanced Analogic Technologies 

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

ΔIL = 30% ⋅ IO = 0.3 · 2 = 600mA

L=

VOUT · (VIN(MAX) - VOUT)

VIN(MAX) ⋅ ΔIL ⋅ fOSC

=

1.8 · (4.2 - 1.8)

4.2 ⋅ 0.6 · 1.2 · 106

= 1.4µH

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

ΔIL =

VO

L

⋅

⎛⎝1

-

VO

VIN

⎞

⎠

· T = 395mA

IPKL

=

IO

+

ΔIL

2

=

2

+

0.395

2

=

2.2A

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

PRODUCT DATASHEET

AAT1153

2A Step-Down Converter

1.8V Output Capacitor

COUT =

3 · ΔILOAD

VDROOP · fS

=

3 · 1.2 = 25µF; use 22µF

0.2 · 1.2 · 106

ESR ≤

ΔVO

ΔIL

0.05

= 0.395 = 0.13Ω

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

ΔVOUT ≤

VOUT · (VIN - VOUT)

VIN · fOSC · L

·

⎛⎝ESR +

1

⎞

8 · fOSC · COUT ⎠

1.8 · (4.2 - 1.8)

⎛

1

⎞

= 4.2 · 1.2 · 106 · 2.2 · 10-6 · ⎝0.01 + 8 · 1.2 · 106 · 22 · 10-6 ⎠ = 5.7mV

IRMS = ΔIL ·0.289 = 0.395 · 0.289 = 114mArms

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

1153.2008.02.1.2

www.analogictech.com

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