AAT2500
1MHz Step-Down Converter/LDO 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)
= 1.0MHz
TAMB = 85°C
1.8V Buck 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
V
L1 ⋅ F
VOBUCK
1.8
V
⎛
⎞
ΔIL1 = OBUCK ⋅ 1 -
=
⋅ 1 -
= 218mA
⎝
VIN
4.7μH ⋅ 1.0MHz
⎝
⎠
ΔI
IPKL1 = IOBUCK
+
L1 = 0.4A + 0.11A = 0.51A
2
PL1 = IOBUCK2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
1.8V Output Capacitor
VDROOP = 0.2V
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
COUT
=
=
= 4.5μF
0.2V · 1MHz
(VOBUCK) · (VIN(MAX) - VOBUCK
)
1
1.8V · (4.2V - 1.8V)
1
·
= 63mArms
IRMS
=
·
=
4.7μH · 1.0MHz · 4.2V
L1 · F · VIN(MAX)
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW
20
2500.2006.05.1.16
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