EUA6019
VOLUME,SEDIFF, and SEMAX Operation
gain step depending on the direction the voltage is
Three pins labeled VOLUME, SEDIFF, and SEMAX changing .If using a DAC to control the volume, set the
control the BTL volume when driving speakers and the SE voltage in the middle of each range to ensure that the
volume when driving headphones. All of these pins are desired gain is achieved.
controlled with a dc voltage, which should not exceed VDD
.
A pictorial representation of the volume control can be
When driving speakers in BTL mode, the VOLUME pin is found in Figure 27.The graph focuses on three gain steps
the only pin that controls the gain. Table 1 shows the gain with the trip points defined in Table 1 for BTL gain. The
for the BTL mode. The voltages listed in the table are for dotted line represents the hysteresis about each gain step.
VDD =5V. For a different VDD, the values in the table scale
linearly. If VDD=4V , multiply all the voltages in the table by
4 V/5V, or 0.8.
The EUA6019 allows the user to specify a difference
between BTL gain and SE gain. This is desirable to avoid
any listening discomfort when plugging in headphones.
When switching to SE mode, the SEDIFF and SEMAX pins
control the singe-ended gain proportional to the gain set by
the voltage on the VOLUME pin,. When SEDIFF =0V, the
difference between the BTL gain and the SE gain is 6dB.
Refer to the section labeled bridged-tied load versus
single-ended load for an explanation on why the gain in
BTL mode is 2x that of single-ended mode, or 6DB greater.
As the voltage on the SEDIFF terminal is increased, the
gain in SE mode decreases. The voltage on the SEDIFF
terminal is subtracted from the voltage on the VOLUME
terminal and this value is used to determine the SE gain.
Some audio systems require that the gain be limited in the
single-ended mode to a level that is comfortable for
headphone listening. Most volume control devices only
have one terminal for setting the gain. For example, if the
speaker gain is 20dB , the gain in the headphone channel is
fixed at 14dB. This level of gain could cause discomfort to
listeners and the SEMAX pin allows the designer to limit
this discomfort when plugging in headphones. The SEMAX
terminal controls the maximum gain for single-ended mode.
The functionality of the SEDIFF and SEMAX pin are
combined to set the SE gain. A block diagram of the
combined functionality is shown in Figure 26. The value
obtained from the block diagram for SE_VOLUME is a dc
voltage that can be used in conjunction with Table 2 to
determine the SE gain. Again, the voltages listed in the
table are for VDD =5V. The values must be scaled for other
values of VDD.
Figure 26. Block diagram of SE Volume Control
Figure 27. DC Volume Control Operation
Table 1 and Table 2 show a range of voltages for each gain
step . There is a gap in the voltage between each gain step .
This gap represents the hysteresis about each trip point in
the internal comparator. The hysteresis ensures that the gain
control is monotonic and does not oscillate form one gain
step to another . If a potentiometer is used to adjust the
voltage on the control terminals, the gain increases as the
potentiometer is turned in one direction and decreases as it
is turned back the other direction. The trip point, where the
gain actually changes , is different depending on whether
the voltage is increased or decreased as a result of the
hysteresis about each trip point. The gaps in Table 1 and
Table 2 can also be through of as indeterminate states where
the gain could be in the next higher gain step or the lower
DS6019 Ver 1.1 May. 2007
14
EUTECH [ EUTECH MICROELECTRONICS INC ]
