PRODUCT DATASHEET
AAT2550178
SystemPowerTM
Total Power Solution for Portable Applications
Step-Down Converter Design Example
Specifications
VOA = 2.5V @ 400mA (VFBA = 0.6V), pulsed load ΔILOAD = 300mA
VOB = 1.8V @ 400mA (VFBB = 0.6V), pulsed load ΔILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 1.4MHz
TAMB= 85°C
2.5V VOA Output Inductor
μsec
A
μsec
A
(see Table 5)
L1 = 3
⋅ VO1 = 3
⋅ 2.5V = 7.5μH
For Sumida inductor CDRH2D14, 6.8μH, DCR = 170mΩ.
⎛
⎞
VO
L1 ⋅ FS
VOA
VIN
2.5
V
2.5V
⎛
⎞
⎠
ΔIA =
⋅ 1 -
⎝
=
⋅ 1 -
= 106mA
⎝
⎠
6.8μH ⋅ 1.4MHz
4.2V
ΔIA
= 0.4A + 0.053A = 0.453A
IPKA = IOA
+
2
2
PLA = IOA ⋅ DCR = 0.452 ⋅ 170mΩ = 34mW
1.8V VOB Output Inductor
μsec
A
μsec
A
(see Table 5)
L2 = 3
⋅ VO2 = 3
⋅ 1.8V = 5.4μH
For Sumida inductor CDRH2D14, 4.7μH, DCR = 135mΩ.
⎛
⎞
⎠
VOB
L ⋅ FS
VOB
VIN
1.8
V
1.8V
4.2V
⎛
⎞
⎠
ΔIB =
⋅ 1 -
⎝
=
⋅ 1 -
= 156mA
⎝
4.7μH ⋅ 1.4MHz
ΔIB
= 0.4A + 0.078A = 0.48A
IPKB = IOB
+
2
2
PLB = IOB ⋅ DCR = 0.4A2 ⋅ 135mΩ = 21.6mW
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2550.2008.02.1.3
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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
