Texas Instruments TLV320AIC26EVM, User Manual

Page: 24 / 46

Circuit Description
3-8
Do not drive the external I
2
S bus when the firmware is loaded and
the onboard microprocessor is active. Disable the micro-
processor by removing JMP3, turn off SW1-1 and SW1-2, and cycle
power to the AIC26EVM in order to use the external I
2
S bus.
3.4.2 Power Supply
Power to the AIC26EVM can be derived directly from the USB interface or
externally supplied through the J9 terminal block or the J10 barrel jack
connector. Supply voltages of 6 VDC to 10 VDC must be supplied from an
external supply. Since it is regulated on the AIC26EVM, this input voltage does
not need to be regulated, as long as it falls within this range. D1 prevents
damage to the board in the event a power supply is connected in reverse
polarity.
U6 regulates the input supply voltage to provide 1.8 V for the AIC26’s digital
core, or the digital IO power supply if the IOVDD is selected as 1.8 V by JMP9.
Also, J3 provides the 3.3 V for the remaining hardware. The regulated supply
voltages have LEDs attached that alert the user that the supply is working. D4
(red) is the indicator for the 1.8-V power supply and D3 (green) is the indicator
for the 3.3-V power supply.
3.4.3 Analog Inputs
Terminal block J3 provides input connection points for the battery and auxiliary
inputs. Battery inputs can range from 0 V to 6 V, and the auxiliary input can
range from 0 V to V
reg
.
Each of these three inputs to the AIC26 internal ADC circuitry has a provision
for an RC filter to be placed in line with the signal. As shipped, all of the resistors
are 0
Ω
and the capacitor is not installed. If noisy conditions prevent obtaining
good readings from the AIC26, 0.01-
µ
F to 0.1-
µ
F capacitors can be installed
in positions C5 through C7. If more filtering is required, the 0-
Ω
resistors should
be unsoldered from the board and replaced with small resistors.
3.4.4 Voltage Reference
The AIC26 has an internal voltage reference, selectable at 1.25 V or 2.5 V. If
an external reference is preferred, the external voltage can be input from J4.
3.4.5 Audio Interface Circuitry
A mono electret microphone can be connected to J5. This jack provides both
audio and bias connections. Bias for the microphone can be supplied either
from the AIC26’s mic bias circuitry or from an external resistor (R11). R11 is
not installed on the AIC26EVM, but can be installed by the user. Internal or
external bias is selected by JMP2.
There is also a small on-board microphone on the EVM, parallel to J5. Without
an external electrical microphone, voice can be input to the AIC26 through this
microphone.
The AIC26 has a built-in headphone amplifier. J6 is the jack for connection to
the amplifier and for driving a 16-
Ω
load at over 25 mW. Also, under audio