PRODUCT DATASHEET
AAT1160
SwitchRegTM
12V, 3A Step-Down DC/DC Converter
Design Example
Specifications
VOUT
VIN
5V @ 3A, Pulsed Load ΔILOAD = 3A
12V nominal
FOSC
TAMB
800kHz
85°C in TDFN34-16 Package
Output Inductor
VOUT · (VIN VOUT
L1 =
-
)
= 3.8µH; see Table 2.
VIN · ΔIL · FOSC
ΔIL = 0.32 · ILOAD
For Coilcraft inductor MSS1038 3.8μH DCR = 13mΩ max.
⎛
⎞
⎠
VOUT
VO1
5
V
5V
⎛
⎞
⎠
ΔI1 =
⋅ 1 -
⎝
=
⋅ 1 -
= 959mA
⎝
L1 ⋅ FOSC
VIN
3.8µH ⋅ 800kHz
12V
ΔI1
2
IPK1 = ILOAD
+
= 3A + 0.479A = 3.48A
2
PL1 = ILOAD ⋅ DCR = 3A2 ⋅ 13mΩ = 117mW
Output Capacitor
VDROOP = 0.2V
3 · ΔILOAD
VDROOP · FOSC
3 · 3A
COUT
=
=
= 56µF; use two 22µF
0.2V · 800kHz
(VOUT) · (VIN(MAX) - VOUT
)
1
5V · (12V - 5V)
1
·
= 277mArms
IRMS(MAX)
=
·
=
3.8µH · 800kHz · 12V
L · FOSC · VIN(MAX)
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (277mA)2 = 384µW
Input Capacitor
Input Ripple VPP = 50mV
1
1
CIN =
=
= 26µF; use 22µF
⎛ VPP
⎝ ILOAD
⎞
⎛ 50mV
⎞
⎠
- ESR · 4 · FOSC
- 5mΩ · 4 · 800kHz
⎠
⎝
3A
ILOAD
IRMS(MAX)
=
= 1.5Arms
2
P = esr · IRMS2 = 5mΩ · (1.5A)2 = 11.25mW
w w w . a n a l o g i c t e c h . c o m
1160.2007.11.1.1
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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
