AAT1145IDE-0.6-T1 View Datasheet(PDF) - Advanced Analogic Technologies
Part Name
Description
MFG CO.
'AAT1145IDE-0.6-T1' PDF : 16 Pages View PDF
SwitchRegTM
PRODUCT DATASHEET
AAT1145
1.5A Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.8V @1.5A
VIN = 2.7V to 4.2V (3.6V nominal)
fS = 1.2MHz
Transient droop = 100mV
∆VO = 50mV
1.8V Output Inductor
ΔIL = 30% ⋅ IO = 0.3 · 1.5 = 450mA
L
=
VOUT · (VIN(MAX) - VOUT)
VIN(MAX) ⋅ ΔIL ⋅ fOSC
=
1.8 · (4.2 - 1.8)
4.2 ⋅ 0.45 · 1.2 · 106
=1.90µH
For Cooper 2.2μH inductor (SD3118-2R2-R) with DCR 74mΩ, the ∆IL should be
ΔIL =
VO
L
⋅
⎛⎝1
-
VO
VIN
⎞
⎠
· T = 341mA
IPKL
=
IO
+
ΔIL
2
=
1.5
+
0.341
2
=
1.67A
PL = IO2 ⋅ DCR = 1.52 ⋅ 0.074 = 166.5mW
1.8V Output Capacitor
COUT =
2 · ΔILOAD
VDROOP · fS
=
2 · 1.2
0.1 · 1.2 · 106
= 20µF; use 22µF
ESR ≤
ΔVO
ΔIL
0.05
= 0.341 = 0.15Ω
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 ⎠ = 6mV
IRMS = ΔIL ·0.289 = 0.341 · 0.289 = 98.5mArms
PCOUT = ESR · IRMS2 = 0.01 · 0.09852 = 97μW
1145.2008.01.1.2
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