AAT1171 Datasheet, PDF (18/22 Pages) Advanced Analogic Technologies – 600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass Switch

DATA SHEET
AAT1171
600mA Voltage-Scaling Step-Down Converter
for RF Power Amplifiers with Bypass Switch
PA Step-Down Converter Design Example
Specifications
V_O(BUCK)
V_IN
F_S
T_AMB
0.6V to 3.4V with R_L =10Ω
2.7V to 4.2V (3.6V nominal)
2.0MHz
85°C
Output Inductor
L1 = 2.2μH
For Copper Electronics SD3112, 2.2μH, DCR = 140mΩ.
ΔI_L1(MAX)
=
L
V_O
⋅ F_S
⋅
⎛⎝_{1 -}
V_O ⎞
V_IN ⎠
=
2.1V
2.2µH ⋅ 2.0MHz
⋅
⎛
⎝^{1 -}
2.1V ⎞
4.2V⎠
= 239mA
The maximum inductor ripple current occurs at 50% duty cycle at the maximum input voltage.
I_PKL1
=
I_O
+
ΔI_L1(MAX)
2
=
0.6A
+
0.118A
=
0.718A
P_L1 = I_O2 ⋅ DCR = 0.6A² ⋅ 140mΩ = 50mW
Output Capacitor
Specify that V_DROOP = 0.2V for a 600mA load pulse.
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.6A
0.2V · 2.0MHz
= 4.5µF
I_RMS
=
1 _· (V_O) · (V_IN(MAX) - V_O) ₌ 1
2· 3 ^{L1 · F}S ^{· V}IN(MAX) 2·
3
· ^{3.4V · (4.2V - 3.4V)}
4.7µH · 2.0MHz · 4.2V
= 69mArms
P_ESR = ESR · I_RMS2 = 5mΩ · (69mA)² = 24µW
Input Capacitor
Specify a maximum input voltage ripple of V_PP = 25mV.
1
1
C_IN(MIN) =
⎛ V_PP
⎝ I_O
- ESR^⎞⎠ · 4 · F_S
=
⎛ 25mV
⎝ 0.6A
= 3.4µF
- 5mΩ⎞⎠ · 4 · 2.0MHz
I_RMS =
I_O
2
= 0.3Arms
P = ESR · I_RMS2 = 5mΩ · (0.3A)² = 0.45mW
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
18
201999B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013