AAT1150_06 Datasheet, PDF (14/17 Pages) Advanced Analogic Technologies – 1MHz 1A Step-Down DC/DC Converter

AAT1150
1MHz 1A Step-Down DC/DC Converter
Design Example
Specifications
I_OUT = 1.0A
I_RIPPLE = 30% of Full Load at Max V_IN
V_OUT = 1.5V
V_IN = 2.7V to 4.2V (3.6V nominal)
F_s = 830kHz
Maximum Input Capacitor Ripple
I_RMS = I_O ⋅
V_O
V_IN
⋅ ^⎛⎝1-
V_O ⎞
V_IN⎠
=
I_O
2
= 0.5A_RMS, V_IN = 2 ⋅ V_O
P = ESR_COUT ⋅ I_RMS2 = 5mΩ ⋅ 0.5² A = 1.25mW
Inductor Selection
L
=
I_O
V_OUT
⋅ k ⋅ F_S
⋅
⎛⎝₁
-
V_OUT⎞
V_IN ⎠
=
1.0A
⋅
1.5V
0.3 ⋅ 830kHz
⋅ ^⎛⎝1 -
1.5V⎞
4.2V⎠
=
3.9μH
Select Sumida inductor CDRH5D18, 4.1μH, 57mΩ, 2.0mm height.
ΔI =
V_O
L ⋅ F_S
⋅ ^⎛⎝1 -
V_O ⎞
V_IN ⎠
=
1.5V
4.1μH ⋅ 830kHz
⋅
⎛
⎝^1-
1.5V ⎞
4.2V⎠
= 280mA
I_PK
=
I_OUT
+
ΔI
2
=
1.0A
+
0.14A
=
1.14A
P = I_O2 ⋅ DCR = 57mW
Output Capacitor Dissipation
I_RMS
=
1
2⋅
⋅
3
V_OUT ⋅ (V_IN - V_OUT) ₌
L ⋅ F_S ⋅ V_IN
1
2⋅
⋅ ^{1.5V ⋅ (4.2V - 1.5V)}
3 4.1μH ⋅ 830kHz ⋅ 4.2V
= 82mA_RMS
P_ESR = ESR_COUT ⋅ I_RMS2 = 5mΩ ⋅ 0.082²A = 33μW
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1150.2006.09.1.5