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AAT1123 Datasheet, PDF (14/18 Pages) Advanced Analogic Technologies – 1MHz Step-Down Converter | |||
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DATA SHEET
AAT1123
1MHz Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ïILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 1.0MHz
TAMB = 85°C
1.8V Output Inductor
L1
=
3
μsec
A
μsec
â
VO2 = 3 A
â
1.8V = 5.4μH
(see
Table
1)
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mï.
ÎIL1 =
VO
L1 â
F
â
ââ1
-
VO â
VIN â
=
1.8V
4.7μH â
1.0MHz
â
1
-
â
â
1.8Vâ
4.2Vâ
=
218mA
IPKL1
=
IO
+
ÎIL1
2
=
0.4A
+
0.11A
=
0.51A
PL1 = IO2 â
DCR = 0.4A2 â
105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.05V
COUT
=
3 · ÎILOAD
VDROOP · FS
=
3 · 0.3A
0.05V · 1MHz
= 18.0μF
IRMS
=
1 · (VO) · (VIN(MAX) - VO) = 1
2· 3
L1 · F · VIN(MAX)
2·
·
3
1.8V · (4.2V - 1.8V) = 63mArms
4.7μH · 1.0MHz · 4.2V
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN = â VPP
â IO
- ESRââ · 4 · FS
=
â 25mV
â 0.4A
- 5mΩââ · 4 · 1MHz
= 4.75µF
IRMS =
IO
2
= 0.2Arms
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
Skyworks Solutions, Inc. ⢠Phone [781] 376-3000 ⢠Fax [781] 376-3100 ⢠sales@skyworksinc.com ⢠www.skyworksinc.com
14
201975B ⢠Skyworks Proprietary Information ⢠Products and Product Information are Subject to Change Without Notice. ⢠March 15, 2013
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