AAT2500 Datasheet, PDF (20/26 Pages) Advanced Analogic Technologies – 1MHz Step-Down Converter/LDO Regulator

AAT2500
1MHz Step-Down Converter/LDO 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
= 1.0MHz
T_AMB = 85°C
1.8V Buck Output Inductor
L1
=
3
μsec
A
⋅
V_O2
=
3
μsec
A
⋅ 1.8V = 5.4μH
(see Table 1)
For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ.
ΔI_L1 =
V_OBUCK
L1 ⋅ F
⋅
⎛⎝_{1 -}
V_OBUCK⎞
V_IN ⎠
=
1.8V
4.7μH ⋅ 1.0MHz
⋅
⎛⎝₁
-
1.8V ⎞
4.2V⎠
=
218mA
I_PKL1
=
I_OBUCK
+
ΔIL1
2
=
0.4A
+
0.11A
=
0.51A
P_L1
=
I²
OBUCK
⋅
DCR
=
0.4A²
⋅
105mΩ
=
17mW
1.8V Output Capacitor
V_DROOP = 0.2V
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.3A
0.2V · 1MHz
=
4.5μF
I_RMS
=
1 _· (V_OBUCK) · (V_IN(MAX) - V_OBUCK) ₌ 1 _·
2· 3
L1 · F · V_IN(MAX)
2· 3
1.8V · (4.2V - 1.8V) _{= 63mArms}
4.7μH · 1.0MHz · 4.2V
P_esr = esr · I_RMS2 = 5mΩ · (63mA)² = 20μW
20
2500.2006.05.1.16