PRODUCT DATASHEET
AAT2789
SystemPowerTM
Low Noise, High Frequency Dual Step-Down Converter
Design Example
Specifications
VO1 = 1.2V @ 1.5A (adjustable using 0.6V version), Pulsed Load ΔILOAD = 1.5A
VO2 = 3.3V @ 500mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 0.5A
VIN = 2.7V to 4.2V (3.6V nominal)
FS1 = 1.8MHz, FS2 = 2MHz
m = 0.75A/μs
TAMB = 85°C in TDFN34-16 Package
Channel 1 Inductor
0.75 ⋅ VO
m
0.75
⋅
1.2V
A
L =
=
= 1.2µH; use 1.5µH
0.75
µs
For TDK inductor LQM2PHN1R5MG0, 1.5μH, DCR = 70mΩ max.
VO1
VO1
1.2V
1.2V
4.2V
⎛
⎞
⎛
· 1 -
⎝
⎞
⎠
ΔI =
· 1 -
⎝
=
= 317mA
L1 ⋅ FS
VIN
1.5µH ⋅ 1.8MHz
⎠
ΔI
2
IPK1
=
IO1
+
= 1.5A + 0.317A = 1.817A
2
PL1 = IOUTBUCK ⋅ DCR = 1.5A2 ⋅ 70mΩ = 158mW
Channel 2 Inductor
0.75 ⋅ VO
m
0.75
⋅
3.3V
A
L =
=
= 3.3µH
0.75
µs
For TDK inductor TFC252008MBT, 3.3μH, DCR = 100mΩ max.
VO1
VO2
3.3V
3.3V
4.2V
⎛
⎞
⎛
· 1 -
⎝
⎞
⎠
ΔI =
· 1 -
⎝
=
= 107mA
L1 ⋅ FS
VIN
3.3µH ⋅ 1.8MHz
⎠
ΔI
2
IPK1
=
IO1
+
= 0.5A + 0.054A = 0.55A
2
PL1 = IOUTBUCK ⋅ DCR = 0.55A2 ⋅ 100mΩ = 30.1mW
w w w . a n a l o g i c t e c h . c o m
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2789.2008.03.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
