Datasheet
SLOS327C − AUGUST 2000 − REVISED MAY 2001
23
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
SE/BTL
operation (continued)
Using a 1/8-in. (3,5 mm) stereo headphone jack, the control switch is closed when no plug is inserted. When
closed, the 100-kΩ/1-kΩ divider pulls the SE/BTL
input low. When a plug is inserted, the 1-kΩ resistor is
disconnected and the SE/BTL
input is 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 (C
O
) into the headphone jack.
PC-BEEP operation
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 normally activated automatically but may be selected
manually through the I
2
C interface. Refer to the I
2
C interface section. 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 0.3 V/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, and then return the amplifier
to shutdown mode.
In auto-detect mode, the amplifier will automatically switch to PC-BEEP mode after detecting a valid signal at
the PC-BEEP input. The preferred input signal is a square wave or pulse train with an amplitude of 1 V
pp
or
greater. To be accurately detected, the signal must have a minimum of 1-V
pp
amplitude, rise and fall times of
less than 0.1 µs, and a minimum of eight rising edges. When the signal is no longer detected, the amplifier will
return to its previous operating mode and volume setting.
When manually selected, the PC-BEEP input is selected, and the LINEIN and HPIN inputs are deactivated
regardless of the input signal.
If it is desired to ac couple the PC-BEEP input, the value of the coupling capacitor should be chosen to satisfy
the following equation:
(14)
C
PCB
w
1
2p f
PCB
(100 kW)
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.