EUA6412
Operation
PC BEEP Operation
SE/BTL
The ability of the EUA6412 to easily switch between
BTL and SE modes is one of its most important cost
saving features. This feature eliminates the requirement
for an additional headphone amplifier in applications
where internal stereo speakers are driven in BTL mode
but external headphone or speakers must be
accommodated. Internal to the EUA6412 , two separate
The PC BEEP input allows a system beep to be sent
directly from a computer through the amplifier to the
speakers with few external components. The input is
activated automatically. When the PC BEEP input is
active, both of the LINEIN and HPIN inputs are
deselected and both the left and right channels are driven
in BTL mode with the signal from PC BEEP. The gain
from the PC BEEP input to the speakers is fixed at
0.3V/V and is independent of the volume setting. When
the PC BEEP input is deselected, the amplifier will
return to the previous operating mode and volume
setting. Furthermore, if the amplifier is in shutdown
mode, activating PC BEEP will take the device out of
shutdown and output the PC BEEP signal, then return
the amplifier to shutdown mode.
amplifiers drive OUT+ and OUT- .The
input
SE/BTL
(terminal 15) control the operation of the follower
amplifier that drives LOUT- and ROUT- (terminals 9
and 16).When
is held low, the amplifier is on
SE/BTL
and the EUA6412 is in the BTL mode. When
is held high, the OUT- amplifiers are in a high
SE/BTL
output impedance state, which configures the EUA6412
as an SE driver from LOUT+ and ROUT+ (terminals 4
and 21). IDD is reduced by approximately one-half in SE
The preferred input signal is a square wave or pulse train
with an amplitude of 1 VPP or greater. When the signal is
no longer detected, the amplifier will return to its
previous operating mode and volume setting.
mode. Control of the
input can be from a
SE/BTL
logic-level CMOS source or, more typically, from a
resistor divider network as shown in Figure 39.
If it is desired to ac-couple the PC BEEP input, the value
of the coupling capacitor should be chosen to satisfy
equation 7:
1
C
≥
− − − − − − − −(7)
PCB
2πf
(100kΩ)
PCB
The PC BEEP input can also be dc- coupled to avoid
using this coupling capacitor. The pin normally sits at
midrail when no signal is present.
Shutdown Modes
The EUA 6412 employs a shutdown mode of operation
designed to reduce supply current, IDD, to the absolute
minimum level during periods of nonuse for
Using a readily available 1/8-in. (3.5mm) stereo
headphone jack, the control switch is closed when no
plug is inserted. When closed the 100-kΩ /1-kΩ divider
battery-power conservation. The
input
SHUTDOWN
terminal should be held high during normal operation
when the amplifier is in use. Pulling low
SHUTDOWN
causes the outputs to mute and the amplifier to enter a
pulls the
input low. When a plug is inserted, the
SE/BTL
1-kΩ resistor is disconnected and the
input is
SE/BTL
low-current state, IDD=150µA.
should
SHUTDOWN
pulled high. When the input goes high, the OUT-
amplifier is shut down causing the speaker to
mute(virtually open-circuits the speaker).The OUT+
amplifier then drives through the output capacitor (CO)
into the headphone jack.
never be left unconnected because amplifier operation
would be unpredictable.
Table 6 .
,
, and Shutdown Function
HP/LINE SE/BTL
Inputs
Amplifier State
INPUT
OUTPUT
SE/BTL
X
Low
High
Low
High
SHUTDOWN
HP/LINE
X
Low
High
High
High
High
X
Mute
BTL
SE
BTL
SE
Low
Line
Line
HP
Low
High
High
HP
X= Do not care
DS6412 Ver 1.0 Dec. 2006
16
EUTECH [ EUTECH MICROELECTRONICS INC ]
