PRODUCT DATASHEET
AAT2146
TM
SwitchReg
Low Noise, FastTransient 600mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO =1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA
VIN =2.7V to 4.2V (3.6V nominal)
FS =2MHz
TAMB=85°C
1.8V Output Inductor
µs
A
µs
A
L1 = 3
⋅ VO2 = 3
⋅ 1.8V = 5.4µH (use 4.7μH; see Table 1)
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mΩ.
⎛
⎞
⎠
VO
L1 ⋅ FS
VO
VIN
1.8
V
1.8V
4.2V
⎛
⋅ 1 -
⎝
⎞
⎠
ΔIL1 =
=
⋅ 1 -
= 109mA
⎝
4.7µH ⋅ 2.0MHz
ΔIL1
2
IPKL1 = IO +
= 0.4A + 0.055A = 0.455A
2
PL1 = IO ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.1V
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
COUT
=
=
= 4.5µF; use 4.7µF
0.1V · 2.0MHz
(VO) · (VIN(MAX) - VO)
L1 · F · VIN(MAX)
1
1.8V · (4.2V - 1.8V)
1
·
= 32mArms
IRMS
=
·
=
4.7µH · 2.0MHz · 4.2V
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (32mA)2 = 6µW
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
=
= 2.17µF; use 2.2µF
⎛ VPP
⎝ IO
⎞
⎛ 25mV
⎝ 0.4A
⎞
⎠
- ESR · 4 · FS
- 5mΩ · 4 · 2.0MHz
⎠
IO
IRMS
=
= 0.2Arms
2
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
w w w . a n a l o g i c t e c h . c o m
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2146.2008.10.1.2
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
