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EUA6011AQIR1

3-W Stereo Audio Power Amplifier with Advanced DC Volume Control

Eutech Microelectronics Inc 

VOLUME,SEDIFF, and SEMAX Operation

Three pins labeled VOLUME, SEDIFF, and SEMAX

control the BTL volume when driving speakers and the SE

volume when driving headphones. All of these pins are

controlled with a dc voltage, which should not exceed VDD.

When driving speakers in BTL mode, the VOLUME pin is

the only pin that controls the gain. Table 1 shows the gain

for the BTL mode. The voltages listed in the table are for

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 EUA6011A 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.

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

EUA6011A

gain step depending on the direction the voltage is

changing .If using a DAC to control the volume, set the

voltage in the middle of each range to ensure that the

desired gain is achieved.

A pictorial representation of the volume control can be

found in Figure 27.The graph focuses on three gain steps

with the trip points defined in Table 1 for BTL gain. The

dotted line represents the hysteresis about each gain step.

Figure 26. Block diagram of SE Volume Control

Figure 27. DC Volume Control Operation

DS6011A Ver 1.0 Mar. 2006

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