AAT1149B Datasheet, PDF (13/17 Pages) Advanced Analogic Technologies – 2.2MHz Fast Transient 400mA Step-Down Converter

DATA SHEET
AAT1149B
2.2MHz Fast Transient 400mA Step-Down Converter
Step-Down Converter Design Example
Specifications
V_O = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load I_LOAD = 300mA
V_IN = 2.7V to 4.2V (3.6V nominal)
F_S = 2.2MHz
T_AMB = 85°C
1.8V Output Inductor
µs
µs
L1 = 1 _A · V_O = 1 _A · 1.8V = 1.8µH
(use 2.2μH)
For Taiyo Yuden inductor CBC2518T2R2M, 2.2μH, DCR = 130m.
ΔI_L1 =
V_O
L1 · F_S
·
1-
V_O
V_IN
=
1.8V
2.2µH · 2.2MHz
·
1-
1.8V
4.2V
= 214mA
I_PKL1
=
I_O
+
ΔI_L1
2
=
0.4A
+
0.107A
=
0.507A
P_L1 = I_O2 · DCR = 0.4A² · 130mΩ = 21mW
1.8V Output Capacitor
V_DROOP = 0.1V
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.3A
0.1V · 2.2MHz
= 4.1µF; use 4.7µF
I_RMS
= ¹ · ^{(VO) · (VIN(MAX) - VO)} = ¹ ·
2· 3 ^{L1 · F}S ^{· V}IN(MAX)
2· 3
1.8V · (4.2V - 1.8V)
2.2µH · 2.2MHz · 4.2V
= 62mArms
P_esr = esr · I_RMS2 = 5mΩ · (62mA)² = 19µW
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201989B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
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