AAT1143 Datasheet, PDF (15/20 Pages) Advanced Analogic Technologies – 1MHz 400mA Step-Down Converter

AAT1143
1MHz 400mA Step-Down Converter
Step-Down Converter Design Example
Specifications
V_O = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ∆I_LOAD = 300mA
V_IN = 2.7V to 4.2V (3.6V nominal)
F_S
= 1.0MHz
T_AMB = 85°C
1.8V Output Inductor
µsec
µsec
L1 = 3 _A ⋅ V_O2 = 3 _A ⋅ 1.8V = 5.4µH _{(see Table 1)}
For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ.
∆I_L1 =
V_O
L1 ⋅ F
⋅
⎛⎝₁
-
V_O ⎞
V_IN ⎠
=
1.8V
4.7µH ⋅ 1.0MHz
⋅
1
-
⎛
⎝
1.8V⎞
4.2V⎠
=
218mA
I_PKL1
=
I_O
+
∆I_L1
2
=
0.4A
+
0.11A
=
0.51A
P_L1 = I_O2 ⋅ DCR = 0.4A² ⋅ 105mΩ = 17mW
1.8V Output Capacitor
V_DROOP = 0.2V
C_OUT
=
3 · ∆I_LOAD
V_DROOP · F_S
=
3 · 0.3A
0.2V · 1MHz
=
4.5µF
I_RMS
=
1 _· (V_O) · (V_IN(MAX) - V_O)
2· 3
L1 · F · V_IN(MAX)
=¹
2·
·
3
1.8V · (4.2V - 1.8V) _{= 63mArms}
4.7µH · 1.0MHz · 4.2V
P_esr = esr · I_RMS2 = 5mΩ · (63mA)² = 20µW
1143.2005.09.1.7
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