AAT1161 Datasheet, PDF (15/18 Pages) Advanced Analogic Technologies – 13.2V Input, 3A Step-Down Converter

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PRODUCT DATASHEET
AAT1161
13.2V Input, 3A Step-Down Converter
Design Example
Specifications
V_OUT
V_IN
F_OSC
T_AMB
5V @ 3A, Pulsed Load ∆I_LOAD = 3A
12V nominal
800kHz
85°C in TDFN34-16 Package
Output Inductor
L1 =
V_OUT · (V_IN
V_IN · ∆I_L
-
·
V_OUT)
F_OSC
=
3.8µH;
see
Table
2.
∆I_L = 0.32 · I_LOAD
For Coilcraft inductor MSS1038 3.8µH DCR = 13mΩ max.
∆I₁ =
V_OUT
L1 ⋅ F_OSC
⋅
⎛⎝₁
-
V_O1
V_IN
⎞
⎠
=
5V
3.8µH ⋅ 800kHz
⋅
⎛⎝₁
-
5V ⎞
12V⎠
=
959mA
I_PK1
=
I_LOAD
+
∆I₁
2
=
3A
+
0.479A
=
3.48A
P_L1
=
I²
LOAD
⋅
DCR
=
3A²
⋅
13mΩ
=
117mW
Output Capacitor
V_DROOP = 0.2V
C_OUT
=
3 · ∆I_LOAD
V_DROOP · F_OSC
=
3 · 3A
0.2V · 800kHz
= 56µF; use three 22µF
I = _RMS(MAX)
1 _· (V_OUT) · (V_IN(MAX) - V_OUT) ₌ 1 _·
2· 3
L · F_OSC · V_IN(MAX)
2· 3
5V · (12V - 5V)
3.8µH · 800kHz · 12V
= 277mArms
P_esr = esr · I_RMS2 = 5mΩ · (277mA)² = 384µW
1161.2008.03.1.0
www.analogictech.com
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