AAT1146IJS-1.2-T1 View Datasheet(PDF) - Analog Technology Inc
Part Name
Description
MFG CO.
'AAT1146IJS-1.2-T1' PDF : 20 Pages View PDF
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PRODUCT DATASHEET
AAT1146
Fast Transient 400mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 1.4MHz
TAMB = 85°C
1.8V Output Inductor
μsec
μsec
L1 = 3 A ⋅ VO2 = 3 A ⋅ 1.8V = 5.4μH (use 4.7μH; see Table 1)
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mΩ.
ΔIL1 =
VO
L1 ⋅ F
⋅
⎛⎝1
-
VO ⎞
VIN ⎠
=
1.8V
4.7µH ⋅ 1.4MHz
⋅
⎛⎝1 -
1.8V ⎞
4.2V ⎠
= 156mA
IPKL1
=
IO
+
ΔIL1
2
=
0.4A
+
0.068A
=
0.468A
PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.1V
COUT
=
3 · ΔILOAD
VDROOP · FS
=
3 · 0.3A
0.1V · 1.4MHz
= 6.4μF; use 10µF
IRMS
=
1 · (VO) · (VIN(MAX) - VO) = 1
2· 3
L1 · F · VIN(MAX)
2·
·
3
1.8V · (4.2V - 1.8V) = 45mArms
4.7μH · 1.4MHz · 4.2V
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN = ⎛ VPP
⎝ IO
- ESR⎞⎠ · 4 · FS
=
⎛ 25mV
⎝ 0.4A
= 3.11μF; use 4.7μF
- 5mΩ⎞⎠ · 4 · 1.4MHz
IRMS =
IO
2
= 0.2Arms
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
16
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1146.2008.06.1.6
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