AAT2505
Dual Channel, Step-Down
Converter/Linear Regulator
Step-Down Converter Design Example
Specifications
VOBUCK = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA
VOLDO = 3.3V @ 300mA
VIN
FS
= 2.7V to 4.2V (3.6V nominal)
= 1.4MHz
TAMB = 85°C
1.8V Buck Output Inductor
µsec
A
µsec
⋅ 1.8V = 5.4µH
A
L1 = 3
⋅ VO2 = 3
(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 -
= 156mA
⎝
4.7μH ⋅ 1.4MHz
ΔIL1
2
IPKL1 = IO +
= 0.4A + 0.068A = 0.468A
2
PL1 = IO ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Buck Output Capacitor
VDROOP = 0.1V
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
COUT
=
=
= 6.4µF; use 10µF
0.1V · 1.4MHz
(VO) · (VIN(MAX) - VO)
L1 · FS · VIN(MAX)
1
·
2· 3
1.8V · (4.2V - 1.8V)
1
= 45mArms
IRMS
=
·
=
4.7µH · 1.4MHz · 4.2V
2· 3
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10
µW
20
2505.2006.06.1.1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
