AAT1162_08 Datasheet, PDF (16/18 Pages) Advanced Analogic Technologies – 12V, 1.5A Step-Down DC/DC Converter

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PRODUCT DATASHEET
AAT1162
12V, 1.5A Step-Down DC/DC Converter
Design Example
Specifications
V_OUT
V_IN
F_OSC
T_AMB
5V @ 1.5A, Pulsed Load ΔI_LOAD = 1.5A
12V nominal
800kHz
85°C in TDFN34-16 Package
Output Inductor
L=
V_OUT
3.3
· 3.8µH = 5.75µH; use 4.7µH (see Table 2)
ΔI_L = 0.32 · I_LOAD = 480mA
For Cooper Bussman inductor DR73-4R7-R 4.7μH DCR = 29.7mW max.
ΔI₁ =
V_OUT
L1 ⋅ F_OSC
⋅
⎛⎝₁
-
V_O1
V_IN
⎞
⎠
=
5V
4.7µH ⋅ 800kHz
⋅
⎛⎝₁
-
5V ⎞
12V⎠
=
480mA
I_PK1
=
I_LOAD
+
ΔI₁
2
=
1.5A
+
0.480A
=
1.98A
P_L1
=
I²
LOAD
⋅
DCR
=
3A²
⋅
13mΩ
=
117mW
Output Capacitor
V_DROOP = 0.2V
C_OUT
= ^{3 · ΔILOAD}
V_DROOP · F_OSC
=
3 · 1.5A
0.2V · 800kHz
= 28µF; use 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)
4.7µH · 800kHz · 12V
= 139mArms
P_esr = esr · I_RMS2 = 5mΩ · (277mA)² = 384µW
Input Capacitor
Input Ripple V_PP = 50mV
1
1
C_IN =
⎛
⎝
V_PP
I_LOAD
-
ESR^⎞⎠ · 4
· F_OSC
=
⎛ 50mV
⎝ 1.5A
- 5mΩ⎞⎠ · 4 · 800kHz
= 11µF; use 10µF
I = _RMS(MAX)
I_LOAD
2
=
0.75Arms
P = esr · I_RMS2 = 5mΩ · (0.75A)² = 2.81mW
16
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1162.2008.01.1.3