AAT1153 Datasheet, PDF (17/19 Pages) Advanced Analogic Technologies – 2A Step-Down Converter

Step-Down Converter Design Example
Specifications
V_O = 1.8V @ 2A
V_IN = 2.7V to 4.2V (3.6V nominal)
f_S = 1.2MHz
Transient droop = 200mV
∆V_O = 50mV
1.8V Output Inductor
ΔI_L = 30% ⋅ I_O = 0.3 · 2 = 600mA
L=
V_OUT · (V_IN(MAX) - V_OUT)
V_IN(MAX) ⋅ ΔI_L ⋅ f_OSC
=
1.8 · (4.2 - 1.8)
4.2 ⋅ 0.6 · 1.2 · 10⁶
= 1.4µH
For Sumida 2.2μH inductor (CDRH2D14) with DCR 75m, the ∆I_L should be:
ΔI_L =
V_O
L
⋅
⎛⎝₁
-
V_O
V_IN
⎞
⎠
· T = 395mA
I_PKL
=
I_O
+
ΔI_L
2
=
2
+
0.395
2
=
2.2A
P_L = I_O2 ⋅ DCR = 2² ⋅ 0.0287 = 114.8mW
DATA SHEET
AAT1153
2A Step-Down Converter
1.8V Output Capacitor
C_OUT =
3 · ΔI_LOAD
V_DROOP · f_S
=
3 · 1.2 _{= 25µF; use 22µF}
0.2 · 1.2 · 10⁶
ESR ≤
ΔV_O
ΔI_L
0.05
= _0.395 = 0.13Ω
Select a 22μF, 10m ESR ceramic capacitor to meet the ripple 50mV requirement.
ΔV_OUT ≤
V_OUT · (V_IN - V_OUT)
V_IN · f_OSC · L
·
⎛⎝_{ESR +}
1
⎞
8 · f_OSC · C_OUT ^⎠
1.8 · (4.2 - 1.8)
⎛
1
⎞
= _{4.2 · 1.2 · 106 · 2.2 · 10-6} · _⎝0.01 + _{8 · 1.2 · 106 · 22 · 10-6 âŽ}  = 5.7mV
I_RMS = I_L ·0.289 = 0.395 · 0.289 = 114mArms
P_COUT = ESR · I_RMS2 = 0.01 · 1² = 10mW
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
17