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AAT2552_08 Datasheet, PDF (26/31 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications | |||
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SystemPowerTM
PRODUCT DATASHEET
AAT2552178
Total Power Solution for Portable Applications
Step-Down Converter Design Example (to be updated)
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 3.0μH; see Table 3)
For Sumida inductor CDRH2D09-3R0, 3.0μH, DCR = 150mΩ.
ÎIL1 =
VO
L1 â
FS
â
ââ1
-
VO â
VIN â
=
1.8V
3.0µH â
1.5MHz
â
â
â
1
-
1.8V
4.2V
â
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
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN = â VPP
â IO
- ESRââ · 4 · FS
=
â 25mV
â 0.2A
= 1.38µF (use 4.7µF)
- 5mΩââ · 4 · 1.5MHz
IRMS =
IO
2
= 0.1Arms
P = esr · IRMS2 = 5mΩ · (0.1A)2 = 0.05mW
26
www.analogictech.com
2552.2008.02.1.2
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