AOZ1017DI Ver la hoja de datos (PDF) - Alpha and Omega Semiconductor
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AOZ1017DI Datasheet PDF : 16 Pages
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AOZ1017D
concern. When designing the compensation loop,
converter stability under all line and load condition must
be considered.
Usually, it is recommended to set the bandwidth to be
less than 1/10 of the switching frequency. The
AOZ1017D operates at a fixed switching frequency
range from 400kHz to 600kHz. It is recommended to
choose a crossover frequency less than 50kHz.
fC = 50kHz
The strategy for choosing RC and CC is to set the cross
over frequency with RC and set the compensator zero
with CC. Using selected crossover frequency, fC, to
calculate RC:
RC = fC × V--V---F-O--B-- × -G----2E---π-A----×-×----C-G----OC----S--
where;
fC is desired crossover frequency,
VFB is 0.8V,
GEA is the error amplifier transconductance, which is 200x10-6
A/V, and
GCS is the current sense circuit transconductance, which is
6.68 A/V.
The compensation capacitor CC and resistor RC together
make a zero. This zero is put somewhere close to the
dominate pole fp1 but lower than 1/5 of selected cross-
over frequency. CC can is selected by:
CC = 2----π-----×-----R1---.-C-5----×-----f--p---1-
The equation above can also be simplified to:
CC = C-----O--R---×--C---R-----L-
An easy-to-use application software which helps to
design and simulate the compensation loop can be found
at www.aosmd.com.
Thermal Management and Layout
Consideration
In the AOZ1017D buck regulator circuit, high pulsing
current flows through two circuit loops. The first loop
starts from the input capacitors, to the VIN pin, to the LX
pins, to the filter inductor, to the output capacitor and
load, and then returns to the input capacitor through
ground. Current flows in the first loop when the high side
switch is on. The second loop starts from inductor, to the
output capacitors and load, to the anode of Schottky
diode, to the cathode of Schottky diode. Current flows in
the second loop when the low side diode is on.
In the PCB layout, minimizing the two loops area reduces
the noise of this circuit and improves efficiency. A ground
plane is strongly recommended to connect the input
capacitor, output capacitor, and PGND pin of the
AOZ1017D.
In the AOZ1017D buck regulator circuit, the major power
dissipating components are the AOZ1017D, the Schottky
diode and output inductor. The total power dissipation of
converter circuit can be measured by input power minus
output power.
Ptotal_loss = VIN × IIN – VO × IO
The power dissipation in Schottky can be approximated
as:
Pdiode_loss = IO × (1 – D) × VFW_Schottky
where;
VFW_Schottky is the Schottky diode forward voltage drop.
The power dissipation of inductor can be approximately
calculated by output current and DCR of inductor.
Pinductor_loss = IO2 × Rinductor × 1.1
The actual junction temperature can be calculated
with power dissipation in the AOZ1017D and thermal
impedance from junction to ambient.
Tjunction =
(Ptotal_loss – Pdiode_loss – Pinductor_loss) × ΘJA + Tamb
Rev. 1.1 April 2009
www.aosmd.com
Page 11 of 16
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