AAT1156 Datasheet, PDF (11/14 Pages) Advanced Analogic Technologies – 1MHz 700mA Step-Down DC-DC Converter

AAT1156
1MHz 700mA Step-Down DC-DC Converter
Design Example
Specifications
I_OUT 0.7A
I_RIPPLE 40% of Full Load at Max V_IN
V_OUT 2.5V
V_IN 2.7V to 4.2V (3.6V nominal)
F_S
1MHz
T_AMB 85°C
Maximum Input Capacitor Ripple:
I_RMS = I_O ·
V_{O · ⎛1-}
V_IN ⎝
V_{O ⎞}
V_IN ⎠
= 0.34Arms,
V_IN =
2x
V_O
P = esr · I_RMS2 = 5mΩ · 0.34² A = 0.6mW
Inductor Selection:
L=
V_OUT
I_O ⋅ k ⋅
F
⋅
⎛⎝₁
-
V_OUT⎞
V_IN ⎠
=
2.5V
0.7A ⋅ 0.3 ⋅ 1MHz
⋅ ^⎛⎝1 -
2.5V ⎞
4.2V⎠
= 4.82µH
Select Sumida inductor CDRH3D16 or CDRH4D28 4.7µH.
∆I =
V_O
L⋅F
⋅
⎛⎝₁
-
V_O
V_IN
⎞
⎠
=
2.5V
4.7µH ⋅ 1MHz
⋅ ^⎛⎝1-
2.5V⎞
4.2V⎠
=
220mA
I_PK
=
I_OUT
+
∆I
2
=
0.7A
+
0.11A
=
0.81A
P = I_O2 ⋅ DCR = (0.7A)² ⋅ 80mΩ = 40mW
1156.2005.11.1.2
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