APA3002 View Datasheet(PDF) - Anpec Electronics
Part Name
Description
Manufacturer
APA3002 Datasheet PDF : 29 Pages
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APA3002
Application Information (Cont.)
Output LC Filter (Cont.)
OUT+ 33µH
0.47µF
OUT- 33µH
0.1µF
0.1µF 8 Ω
DC Volume
Figure 2. LC Output Filter
Decreasing VVOLUME
3.1
0.5
Increasing VVOLUME
-2.0
(39.7% x VVREF)
1.90
(37.9% x VVREF)
1.99 2.01
2.12
(40.1% x VVREF) (41.9% x VVREF)
Volume’s Voltage (V)
Figure 3. DC Volume Control Operation (VVREF=5V)
The Class-D’s gain is determined by the voltage of VOL-
UME control pin. “Class-D DC Volume Control Table” lists
the gain in Class-D that is determined by the VOLUME
pin’s voltage (V ) in reference to the VREF’s voltage
VOLUME
(V ). The maximum voltage of VOLUME should not
VREF
exceed the VREF’s voltage.
If the resistor divider fixed the Class-D’s gain is used,
and then the resistor divider values to center the volt-
age between the two percentage points of the table’s
column “Increasing V ” need to be calculated, see
VOLUME
figure 3. The resistor can be connected between VREF
and REFGND, and then VREF and LDOREF are con-
nected together.
If a DAC controls the Class-D gain is used, VREF and
REFGND should be connected to the reference voltage
for the DAC and the GND terminal of the DAC respectively.
For the DAC application, LDOREF would be left
unconnected. The reference voltage of the DAC provides
the reference to the internal gain circuitry through the
VREF input and any fluctuations in the DAC output voltage
will not affect the Class-D gain.
The percentages in the “Increasing V ”of table should
VOLUME
be used for setting the voltages of the DAC when the
voltage on the VOLUME pin is increased. The percent-
ages in the “ decreasing VVOLUME” of the table should be
used for the DAC voltages when decreasing the voltage
on the VOLUME pin. Two lookup tables should be used
in software to control the gain based on an increase or
decrease in the desired system volume.
If using an analog potentiometer to control the gain, it
should be connected between VREF and REFGND.
VREF can be connected to LDODREF or an external
voltage source, if desired. The table of “Increasing VVOLUME”
and “Decreasing VVOLUME” in “Class-D DC Volume Control
Table” should be used to determine the point at which
gain changes depending on the direction that the poten-
tiometer is turned. If the voltage on the center tap of the
potentiometer is increasing, the table “Increasing VVOLUME”
at “Class-D DC Volume Control Table” should be refer-
enced to determine the trip points. If the voltage is
decreasing, the trip points in the ”Decreasing V ”
VOLUME
should be referenced.
The trip point, where the gain actually changes, is various
depending on whether the voltage on the VOLUME pin is
increasing or decreasing as a result of hysteresis about
each trip point. The hysteresis ensures that the gain con-
trol is monotonic and does not oscillate from one gain
step to another. A pictorial representation of the volume
control can be found in Figure 3. The graph focuses on
three gain steps with the trip points defined in the table
“Increasing VVOLUME” and ”Decreasing VVOLUME” of “Class-
D DC Volume Control Table” for Class-D gain. The dotted
lines represent the hysteresis about each gain step.
Copyright © ANPEC Electronics Corp.
21
Rev. A.6 - Sep., 2009
www.anpec.com.tw
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