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| AAT1121 Datasheet, PDF (15/20 Pages) Advanced Analogic Technologies – 1.5MHz, 250mA Step-Down Converter | |||
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AAT1121
1.5MHz, 250mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.8V @ 250mA, Pulsed Load ÎILOAD = 200mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS
= 1.5MHz
TAMB = 85°C
1.8V Output Inductor
µsec
µsec
L1 = 1.67 A â
VO2 = 1.67 A â
1.8V = 3µH
(use 3.3μH; see Table 1)
For Sumida inductor CDRH2D09-3R0, 3.3μH, DCR = 150mΩ.
ÎIL1 =
VO
L1 â
F
â
ââ1
-
VO â
VIN â
=
1.8V
3.0µH â
1.5MHz
â
ââ1 -
1.8V â
4.2V â
= 228mA
IPKL1
=
IO
+
ÎIL1
2
=
250mA
+
114mA
=
364mA
PL1 = IO2 â
DCR = 250mA2 â
150mΩ = 9.375mW
1.8V Output Capacitor
VDROOP = 0.1V
COUT
=
3 · ÎILOAD
VDROOP · FS
=
3 · 0.2A
0.1V · 1.5MHz
= 4µF; use 4.7µF
IRMS
=
1 · (VO) · (VIN(MAX) - VO) = 1 ·
2· 3
L1 · FS · VIN(MAX) 2· 3
1.8V · (4.2V - 1.8V) = 66mArms
3.0µH · 1.5MHz · 4.2V
Pesr = esr · IRMS2 = 5mΩ · (66mA)2 = 21.8µW
1121.2006.04.1.0
15
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