AIC1899PK Ver la hoja de datos (PDF) - Analog Intergrations
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AIC1899PK Datasheet PDF : 10 Pages
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AIC1899
APPLICATION INFORMATION
The AIC1899 operates well with a variety of
external components. The components in Figure 1
are suitable for most applications. See the
following sections to optimize external
components for a particular application.
Inductor Selection
A 22µH inductor is recommended for most
AIC1899 applications. Although small size and
high efficiency are major concerns, the inductor
should have low core losses at 1.0MHz and low
DCR (copper wire resistance).
Inductor selection depends on input voltage,
output voltage, maximum current, size, and
availability of inductor values. Other factors can
include efficiency and ripple voltage. Inductors are
specified by their inductance (L), peak current
(IL(PK)), and resistance (DCR). The following
step-up circuit equations are useful in choosing
the inductor values based on the application. They
allow the trading of peak current and inductor
value while considering component availability
and cost.
The equation used here assumes a constant K,
which is the ratio of the inductor peak-to-peak AC
current to average DC inductor current. A good
compromise between the size of the inductor
versus loss and output ripple is to choose a K of
0.3 to 0.5. The peak inductor current is then given
by:
iL( pk )
=
I o(max) ⋅Vo
η ⋅Vi(min)
⋅ 1 +
K
2
where:
IO(max): Maximum output current, (A)
Vi(min): Minimum input voltage, (V)
η : Conversion efficiency, 0.8
K = ∆iL : Ratio of the inductor peak-to-peak
IL
AC current to average DC
inductor current
The inductance value is then given by:
L = Vi(min) 2 ⋅η ⋅ D
K ⋅ f ⋅Vo ⋅ I o(max)
where:
D = Duty cycle =
Vi(min) − (V f + Vo )
I i(max) ⋅ Rds(on) − (V f + Vo )
V f : Catch diode forward drop
f : Switching frequency
Capacitor Selection
The AIC1899 operates with both tantalum and
ceramic output capacitors. When using tantalum
capacitors, the zero caused by the ESR of the
tantalum is used to ensure stability. When using
ceramic capacitors, the zero due to the ESR will
be at too high a frequency to be useful in
stabilizing the control loop. When using ceramic
capacitors, add a feedforward capacitor to
increase the phase margin, improving the
control-loop stability.
Diode Selection
Schottky diodes, with their low forward voltage
drop and fast reverse recovery, are the ideal
choices for AIC1899 applications. The forward
voltage drop of an Schottky diode represents the
conduction losses in the diode, while the diode
capacitance (CT or CD) represents the switching
losses. For diode selection, both forward voltage
drop and diode capacitance need to be
considered. Schottky diodes with higher current
ratings usually have lower forward voltage drop
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