AAT1110_06 Datasheet, PDF (16/19 Pages) Advanced Analogic Technologies – Fast Transient 800mA Step-Down Converter

AAT1110
Fast Transient 800mA Step-Down Converter
Step-Down Converter Design Example
Specifications
V_O = 1.8V @ 600mA (adjustable using 0.6V version), Pulsed Load ΔI_LOAD = 300mA
V_IN = 2.7V to 4.2V (3.6V nominal)
F_S
= 1.4MHz
T_AMB = 85°C
1.8V Output Inductor
μsec
μsec
L1 = 3 _A ⋅ V_O2 = 3 _A ⋅ 1.8V = 5.4μH
(use 4.7µH; see Table 1)
For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ.
ΔI_L1 =
V_O
L1 ⋅ F
⋅
⎛⎝₁
-
V_O ⎞
V_IN ⎠
=
1.8V
4.7μH ⋅ 1.4MHz
⋅
⎛⎝_{1 -}
1.8V ⎞
4.2V ⎠
= 156mA
I_PKL1
=
I_O
+
ΔIL1
2
=
0.6A
+
0.068A
=
0.668A
P_L1 = I_O2 ⋅ DCR = 0.6A² ⋅ 105mΩ = 38mW
1.8V Output Capacitor
V_DROOP = 0.1V
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.3A
0.1V · 1.4MHz
= 6.4μF; use 10µF
I_RMS
=
1 _· (V_O) · (V_IN(MAX) - V_O) ₌ 1
2· 3
L1 · F · V_IN(MAX)
2·
·
3
1.8V · (4.2V - 1.8V) _{= 45mArms}
4.7μH · 1.4MHz · 4.2V
P_esr = esr · I_RMS2 = 5mΩ · (45mA)² = 10μW
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1110.2006.04.1.0