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| AAT1149A Datasheet, PDF (13/17 Pages) Advanced Analogic Technologies – 2.2MHz Fast Transient 400mA Step-Down Converter | |||
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PRODUCT DATASHEET
AAT1149A
2.2MHz Fast Transient 400mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.875V @ 400mA (adjustable using 0.6V version), Pulsed Load DILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 2.2MHz
TAMB = 85°C
1.875V Output Inductor
µs
µs
L1 = 1 A · VO = 1 A · 1.875V = 1.875µH
(use 2.2μH)
For Taiyo Yuden inductor CBC2518T2R2M, 2.2μH, DCR = 130mΩ.
ÎIL1 =
VO
L1 · FS
·
1-
VO
VIN
=
1.875V
2.2µH · 2.2MHz
·
1
-
1.875V
4.2V
= 214mA
IPKL1
=
IO
+
ÎIL1
2
=
0.4A
+
0.107A
=
0.507A
PL1 = IO2 · DCR = 0.4A2 · 130mΩ = 21mW
1.875V Output Capacitor
VDROOP = 0.1V
COUT
=
3 · ÎILOAD
VDROOP · FS
=
3 · 0.3A
0.1V · 2.2MHz
= 4.1µF; use 4.7µF
IRMS
=
1 · (VO) · (VIN(MAX) - VO) = 1
2· 3 L1 · FS · VIN(MAX)
2·
·
3
1.875V · (4.2V - 1.875V) = 62mArms
2.2µH · 2.2MHz · 4.2V
Pesr = esr · IRMS2 = 5mΩ · (62mA)2 = 19µW
1149A.2008.08.1.1
www.analogictech.com
13
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