AAT1123
1MHz Step-Down Converter
Step-Down Converter Design Example
Specifications
VO
VIN
FS
= 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA
= 2.7V to 4.2V (3.6V nominal)
= 1.0MHz
TAMB = 85°C
1.8V Output Inductor
μsec
A
μsec
A
L1 = 3
⋅ VO2 = 3
⋅ 1.8V = 5.4μH
(see Table 1)
For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ.
⎛
⎝
⎞
1.8V
⎠
4.2V
VO
L1 ⋅ F
VO
VIN
1.8
V
⎛
⋅ 1 -
⎝
⎞
⎠
ΔIL1
=
=
⋅ 1 -
= 218mA
4.7μH ⋅ 1.0MHz
ΔI
IPKL1 = IO + L1 = 0.4A + 0.11A = 0.51A
2
PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.05V
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
COUT
=
=
= 18.0μF
0.05V · 1MHz
(VO) · (VIN(MAX) - VO)
L1 · F · VIN(MAX)
1
1.8V · (4.2V - 1.8V)
1
·
= 63mArms
IRMS
=
·
=
4.7μH · 1.0MHz · 4.2V
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW
1123.2006.05.1.5
15
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
