AAT2550_08 Datasheet, PDF (31/34 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

SystemPower^TM
PRODUCT DATASHEET
AAT2550178
Total Power Solution for Portable Applications
Step-Down Converter Design Example
Specifications
V_OA = 2.5V @ 400mA (V_FBA = 0.6V), pulsed load ΔI_LOAD = 300mA
V_OB = 1.8V @ 400mA (V_FBB = 0.6V), pulsed load ΔI_LOAD = 300mA
V_IN = 2.7V to 4.2V (3.6V nominal)
F_S = 1.4MHz
T_AMB = 85°C
2.5V V_OA Output Inductor
μsec
L1 = 3 _A
⋅
V_O1
=
3
μsec
A
⋅ 2.5V = 7.5μH
(see Table
5)
For Sumida inductor CDRH2D14, 6.8μH, DCR = 170mΩ.
ΔIA =
V_O
L1 ⋅ F_S
⋅ ^⎛⎝1
-
V_OA⎞
V_IN ⎠
=
2.5V
6.8μH ⋅ 1.4MHz
⋅
⎛
⎝¹
-
2.5V⎞
4.2V⎠
= 106mA
I_PKA
=
I_OA
+
ΔIA
2
=
0.4A
+
0.053A
=
0.453A
P_LA = I_OA2 ⋅ DCR = 0.45² ⋅ 170mΩ = 34mW
1.8V V_OB Output Inductor
μsec
μsec
L2 = 3 _A ⋅ V_O2 = 3 _A ⋅ 1.8V = 5.4μH (see Table 5)
For Sumida inductor CDRH2D14, 4.7μH, DCR = 135mΩ.
ΔIB
=
V_OB
L ⋅ F_S
⋅
⎛⎝₁
-
V_OB
V_IN
⎞
⎠
=
1.8V
4.7μH ⋅ 1.4MHz
⋅
⎛
⎝¹
-14..82VV^⎞⎠
= 156mA
I_PKB
=
I_OB
+
ΔIB
2
=
0.4A
+
0.078A
=
0.48A
P_LB = I_OB2 ⋅ DCR = 0.4A² ⋅ 135mΩ = 21.6mW
2550.2008.02.1.3
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