Texas Instruments TLV320AIC26EVM, User Manual

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Circuit Description
3-7 Operation
3.3.6 Analog Input Connector
The auxiliary and battery inputs to the touch screen controller are brought onto
the EVM board through terminal block J3. The pinout is shown in Table 3−8.
Table 3−8. Analog Input Connector
Reference
Designator
Description
Pin
Number Signal
Name
Function
1 VBAT1 Battery input 1, 0 V to 6 V
Battery and auxiliary inputs to the touch
2 VBAT2 Battery input 2, 0 V to 6 V
J3
Battery and auxiliary inputs to the touch
screen control
3 AUX Auxiliary input, 0 V to VREF
4 GND Ground
3.4 Circuit Description
The AIC26 evaluation kit circuitry consists of a USB microprocessor, power
supply circuitry, analog input interfaces, and audio interface circuitry (both
analog and digital). These circuits are described in the following sections.
3.4.1 USB Microprocessor
The AIC26EVM has a USB interface for connecting to a PC. This connection
is made through a TAS1020B streaming audio processor, U5.
The SPI interface to the AIC26 can be controlled from two sources: the
external SPI header, J12, or through the onboard microprocessor (U5) via
USB. The U5 outputs are enabled only when the supplied firmware is loaded
and the TAS SPI switch SW1-3 is turned on. The firmware resides in the serial
EEPROM chip (U2). U5 only loads firmware from U2 when U2’s A1 address
line is pulled low. To disable firmware loading, A1 must be high, by having JM3
removed.
When the firmware is loaded and active, D2 (a yellow LED) is lit.
If no firmware is loaded, U3’s outputs are in 3-state, allowing the external SPI
bus to drive the AIC26 and turn off SW1-3 to ensure the isolation of the
TAS1020B from the SPI bus. When the firmware is loaded, the PC software
enables the microprocessor to control the SPI bus.
Do not drive the external SPI bus when the firmware is loaded and
the onboard microprocessor is active. Disable the micro-
processor by removing JMP3, turn off SW1-3, and cycle power to
the AIC26EVM in order to use the external SPI bus.
Each signal from the SPI inputs is connected directly to the AIC26. As such,
signals on these pins must not exceed the power supply voltage of the AIC26,
which is 3.3 V on this EVM.
Likewise, the I
2
S signals for the digital audio can be driven either externally by
J11 or by the USB audio controller (U5).