User's Manual

13
Right channel audio inputs. This dual audio input can be configured to be either single-ended or fully
differential and programmed for either microphone or line input. Route differential pairs close to each
other and use a solid dedicated audio ground plane for the audio signals.
AUDI O_ I N _ P_ LEFT a n d AUD I O_ I N _ N _ LEFT
Left channel audio input. ESD protection and layout considerations similar to right channel audio should
be used.
AUDI O_ OUT_ P_ RI GH T and AUD I O_ OUT_ N _ RI GHT
Right channel audio output. The audio output lines should be routed differentially to either the speakers
or to the output amplifier, depending on whether or not a single-ended signal is required. Use low
impedance ground plane dedicated for the audio signals.
AUDI O_ OUT_ P_ LEFT a nd AUD I O_ OUT_ N _ LEFT
Left channel audio output. The same guidelines apply to this section as discussed previously.
MI C_ BI AS
Bias voltage output for a microphone. Use the same layout guidelines as discussed previously with
other audio signals.
LED0
TBM–CBC5 includes a pad dedicated to driving LED indicators. This terminal may be controlled by firmware
and it can also be set by the battery charger. The terminal is an open-drain output, so the LED must be
connected from a positive supply rail to the pad in series with a current limiting resistor.
It is recommended that the LED pad is operated with a pad voltage below 0.5V. In this case, the pad
can be thought of as a resistor, RON. The resistance together with the external series resistor will set
the current, ILED, in the LED. Value for the external series resistance can be calculated from the
Equation 1
ON
LED
F
LED
R
I
VVDD
R −
−
=
Equat ion 1 : LED series resist or
Where V
F
is the forward voltage drop of the LED, I
LED
is the forward current of the LED and R
ON
is the
on resistance (typically 20 Ω) of the LED driver.