Datasheet

Circuit Description
3-8
3.3.4 Keyboard Interface
A 4x4 matrix keypad is included with the TSC2301EVM. This keypad connects
directly to the TSC2301. No other circuitry is needed since the TSC2301
contains all the keypad control circuitry.
3.3.5 LCD BIas D/A Converter Circuit
The TSC2301 contains a current-output D/A converter, which is designed to
be used with a two resistor pullup network to turn the current into a voltage.
The details of the operation of this D/A converter can be found in the TSC2301
data sheet.
On this board, provision is made for the user to provide two resistors, in R2 and
R3 sockets.
R1 is the range setting resistor for the TSC2301 DAC, and is installed in a
socket so that it can be replaced with a different value. With the factory
installed value of 100 KΩ, the DAC has a range of 600 µA.
3.3.6 Audio Interface Circuitry
J3 is a stereo 3.5-mm jack for connecting line-level inputs to the TSC2301.
Each channel is presented to an attenuator (for example R11, R13) and a small
capacitor to provide some antialiasing ( for example C17), then AC-coupled
into the TSC2301 (for example, through C12). The attenuator may be defeated
by JMP2, or JMP3.
Line outputs from the TSC2301 are routed to J5 through a similar network and
are AC-coupled. The mono output from the TSC2301 is sent to U2, whose
output is then connected to J2. An 8-Ω or greater speaker can be connected
between the two terminals.
A mono electret microphone may be connected to J4. This jack provides both
audio and bias connections. Bias for the microphone can be supplied either
from the TSC2301’s mic bias circuitry, or from an external resistor, R15. R15
is not installed on the TSC2301EVM, but can be installed by the user. Internal
or external bias is selected by JMP4.
The TSC2301 has a built-in headphone amplifier. J6 is a jack for connection
to headphones, with AC-coupling provided on the EVM.