PRODUCT DATASHEET
AAT1153
2A Step-Down Converter
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
VOUT · (VIN(MAX) - VOUT
)
1.8 · (4.2 - 1.8)
L =
=
= 1.4µH
VIN(MAX) ⋅ ΔIL ⋅ fOSC
4.2 ⋅ 0.6 · 1.2 · 106
For Sumida 2.2μH inductor (CDRH2D14) with DCR 75mΩ, the ∆IL should be
VO
VO
⎛
⎞
⎠
ΔIL =
⋅ 1 -
⎝
· T = 395mA
L
VIN
ΔIL
2
0.395
= 2.2A
2
IPKL = IO +
= 2 +
2
PL = IO ⋅ DCR = 22 ⋅ 0.0287 = 114.8mW
1.8V Output Capacitor
3 · ΔILOAD
VDROOP · fS
3 · 1.2
COUT
=
=
= 25µF; use 22µF
0.2 · 1.2 · 106
ΔVO
ΔIL
0.05
ESR ≤
=
= 0.13Ω
0.395
Select a 22μF, 10mΩ ESR ceramic capacitor to meet the ripple 50mV requirement.
VOUT · (VIN - VOUT
)
1
⎛
⎞
⎠
ΔVOUT
≤
· ESR +
⎝
VIN · fOSC · L
8 · fOSC · COUT
1.8 · (4.2 - 1.8)
1
⎛
⎞
⎠
=
· 0.01 +
= 5.7mV
4.2 · 1.2 · 106 · 2.2 · 10-6
8 · 1.2 · 106 · 22 · 10-6
⎝
IRMS = ΔIL ·0.289 = 0.395 · 0.289 = 114mArms
PCOUT = ESR · IRMS2 = 0.01 · 12 = 10mW
w w w . a n a l o g i c t e c h . c o m
1153.2007.11.1.1
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