AAT2148 Datasheet, PDF (15/18 Pages) Skyworks Solutions Inc. – Low-Noise, Fast Transient 1A Step-Down Converter

DATA SHEET
AAT2148
Low-Noise, Fast Transient 1A Step-Down Converter
Step-Down Converter Design Example
Specifications
V_O = 1.8V @ 1A (adjustable using 0.6V version), Pulsed Load I_LOAD = 300mA
V_IN = 2.7V to 4.2V (3.6V nominal)
F_S = 2MHz
T_AMB = 85°C
1.8V Output Inductor
L1
=
3
µs
A
·
V_O1
=
3
µs
A
· 1.8V = 5.4µH(use
4.7μH;
see
Table
1)
For Coilcraft inductor SD3118, 4.7μH, DCR = 162m.
ΔI_L1
=
V_O
L1 · F_S
·
1-
V_O
V_IN
=
1.8V
4.7µH · 2.0MHz
·
1
-
1.8V
4.2V
= 109mA
I_PKL1
=
I_O
+
ΔI_L1
2
=
1A
+
0.055A
=
1.055A
P_L1 = I_O2 · DCR = 1A² · 162mΩ = 162mW
1.8V Output Capacitor
V_DROOP = 0.1V
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.3A
0.1V · 2.0MHz
= 4.5µF; use 4.7µF
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) _{= 32mArms}
4.7µH · 2.0MHz · 4.2V
P_esr = esr · I_RMS2 = 5mΩ · (32mA)² = 6µW
Input Capacitor
Input Ripple V_PP = 30mV
C_IN =
1
=
V_PP
I_O
- ESR
· 4 · F_S
1
= 5μF; use 4.7μF
30mV
1A
- 5mW
· 4 · 2.0MHz
I_RMS =
I_O
2
= 0.5Arms
P = ESR · I_RMS2 = 5mΩ · (0.5A)² = 1.25mW
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
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