AAT2505 Datasheet, PDF (20/26 Pages) Advanced Analogic Technologies – Dual Channel, Step-Down Converter/Linear Regulator

AAT2505
Dual Channel, Step-Down
Converter/Linear Regulator
Step-Down Converter Design Example
Specifications
V_OBUCK = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔI_LOAD = 300mA
V_OLDO = 3.3V @ 300mA
V_IN = 2.7V to 4.2V (3.6V nominal)
F_S
= 1.4MHz
T_AMB = 85°C
1.8V Buck Output Inductor
L1
=
3
µsec
A
⋅
V_O2
=
3
µsec
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_S
⋅
⎛⎝_{1 -}
V_O ⎞
V_IN ⎠
=
1.8V
4.7μH ⋅ 1.4MHz
⋅
⎛⎝_{1 -}
1.8V ⎞
4.2V ⎠
= 156mA
I_PKL1
=
I_O
+
ΔIL1
2
=
0.4A
+
0.068A
=
0.468A
P_L1 = I_O2 ⋅ DCR = 0.4A² ⋅ 105mΩ = 17mW
1.8V Buck 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
2·
· ^{(VO) · (VIN(MAX) - VO)} = ¹ ·
3 ^{L1 · F}S ^{· 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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2505.2006.06.1.1