Platform Signal Routing And Outputs - Texas Instruments TPA721 User Manual

3.3.2 Signal Routing
Signal flow on the platform is controlled by two signal routing switches, as
shown in Figure 3 – 5.
Figure 3–5. Platform Signal Routing and Outputs
R
U1
Audio
Signal
Input
Conditioning
L
3.3.2.1 Signal Conditioning
The audio signal from the input jacks can be applied to the signal conditioning
socket (U1) if an EVM is installed there, or socket U1 can be bypassed and the
audio input signal applied directly to the inputs of the TPA721 power amplifiers.
3.3.3 Mute/Mode
The TPA721 MSOP EVM is equipped with a shutdown (mute) control input pin.
When this input is tied to V
down and assumes a low-power mode. When the EVM control input is tied to
GND or allowed to float, amplifier operation resumes.
In typical applications, as often found in notebook computers, portable audio
products, and such, the internal speakers mute when headphones are
plugged into the headphone jack, or internal speakers mute when external
speakers are connected. In applications using separate speaker and
headphone amplifiers, the one not being used can be shut down (muted) to
conserve power.
3.3.3.1 Headphone Jack Control Signals
The platform headphone output jack (J10) contains an internal switch that
changes the state of a pair of control lines when a plug is inserted (Figure 3 – 6).
Each control line is pulled down by a 1-kΩ resistor to ground (R4 and R5). The
switch in the headphone jack pulls one line or the other up to V
240 Ω resistor (R3) depending on whether or not a plug is inserted in J10.
Using The TPA721 MSOP EVM With the Plug-N-Play Evaluation Platform
Off
U3
TPA721
Amplifier EVM
S2
U4
TPA721
Amplifier EVM
On
U5
Stereo
Headphone
Amplifier
Switch S2 selects signal conditioning or bypasses it
, the TPA721 amplifier IC on the module shuts
DD
+
R R
–
–
L L
+
U2 – U4
R
+
R
–
GND
S3
L
–
+
L
U5
Details
J7, J8, J9
Speaker
Outputs
J10
Headphone
Output
through a
DD
3-7