AAT2789 Datasheet, PDF (18/22 Pages) Advanced Analogic Technologies – Low Noise, High Frequency Dual Step-Down Converter

SystemPower^TM
PRODUCT DATASHEET
AAT2789
Low Noise, High Frequency Dual Step-Down Converter
Design Example
Specifications
V_O1 = 1.2V @ 1.5A (adjustable using 0.6V version), Pulsed Load ΔI_LOAD = 1.5A
V_O2 = 3.3V @ 500mA (adjustable using 0.6V version), Pulsed Load ΔI_LOAD = 0.5A
V_IN = 2.7V to 4.2V (3.6V nominal)
F_S1 = 1.8MHz, F_S2 = 2MHz
m = 0.75A/μs
T_AMB = 85°C in TDFN34-16 Package
Channel 1 Inductor
L=
0.75 ⋅ V_O
m
=
0.75 ⋅ 1.2V
A
= 1.2µH; use 1.5µH
0.75 _µs
For TDK inductor LQM2PHN1R5MG0, 1.5μH, DCR = 70mΩ max.
ΔI
=
V_O1
L₁ ⋅ F_S
· ^⎛⎝1
-
V_O1⎞
V_IN⎠
=
1.2V
1.5µH ⋅ 1.8MHz
·
⎛⎝₁
-
1.2V⎞
4.2V⎠
=
317mA
ΔI
I_PK1 = I_O1 + ₂ = 1.5A + 0.317A = 1.817A
P_L1
=
I²
OUTBUCK
⋅
DCR
=
1.5A²
⋅
70mΩ
=
158mW
Channel 2 Inductor
L=
0.75 ⋅ V_O
m
=
0.75 ⋅ 3.3V
A
= 3.3µH
0.75 _µs
For TDK inductor TFC252008MBT, 3.3μH, DCR = 100mΩ max.
ΔI
=
V_O1
L₁ ⋅ F_S
· ^⎛⎝1
-
V_O2⎞
V_IN⎠
=
3.3V
3.3µH ⋅ 1.8MHz
·
⎛⎝₁
-
3.3V⎞
4.2V⎠
=
107mA
ΔI
I_PK1 = I_O1 + ₂ = 0.5A + 0.054A = 0.55A
P_L1
=
I²
OUTBUCK
⋅
DCR
=
0.55A²
⋅
100mΩ
=
30.1mW
18
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2789.2008.03.1.0