AAT2500M Datasheet, PDF (18/22 Pages) Advanced Analogic Technologies – 400mA Step-Down Converter and 300mA LDO

AAT2500M
400mA Step-Down Converter and 300mA LDO
Step-Down Converter Design Example
Specifications
V_OBUCK = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ∆I_LOAD = 300mA
V_OLDO = 3.3V @ 300mA
V_IN = 2.7V to 4.2V (3.6V nominal)
F_OSC = 1.8MHz
T_AMB = 85°C
1.8V Buck Output Inductor
µsec
µsec
L1 = 1.5 _A ⋅ V_OBUCK = 1.5 _A ⋅ 1.8V = 2.7µH (see Table 1)
For Sumida inductor CDRH3D16, 2.2µH, DCR = 59mΩ.
∆I_L1 =
V_OBUCK
L1 ⋅ F
⋅
⎛⎝_{1 -}
V_OBUCK⎞
V_IN ⎠
=
1.8V
2.2µH ⋅ 1.8MHz
⋅
⎛
⎝¹
-
1.8V ⎞
4.2V⎠
=
260mA
I_PKL1
=
I_OBUCK
+
∆I_L1
2
=
0.4A
+
0.130A
=
0.53A
P_L1
=
I²
OBUCK
⋅
DCR
=
(0.4A)²
⋅
59mΩ
=
9.4mW
1.8V Output Capacitor
V_DROOP = 0.2V
C_OUT
=
3 · ∆I_LOAD
V_DROOP · F_OSC
= ^{3 · 0.3A} = 2.5µF
0.2V · 1.8MHz
I_RMS
=
1 _· (V_OBUCK) · (V_IN(MAX) - V_OBUCK) ₌ 1 _·
2· 3
L1 · F_OSC · V_IN(MAX)
2· 3
1.8V
2.2µH
·
·
(4.2V - 1.8V)
1.8MHz · 4.2V
=
75mA_RMS
P_esr = esr · I_RMS2 = 5mΩ · (75mA)² = 28.1µW
18
2500M.2007.06.1.0