Analog Evaluation
11
SLVUBT6A – October 2019 – Revised May 2020
Copyright © 2019–2020, Texas Instruments Incorporated
Using the TPS8804EVM
Figure 10. CO Connectivity Test with Sensor
3.2
Photo AFE Evaluation
Connect the photoelectric chamber to the EVM. If a photoelectric chamber is not available, place a box
over the EVM to block ambient light and reflect the EVM LED light into the photodiode when testing the
photo AFE.
Enable the photo amplifier, photo gain amplifier, and set the
AMUX SELECTION
to
PHOTO GAIN
AMPLIFIER
. Select the photo reference on the EVM with jumper J7 and enable the photo reference
voltage if the reference is set to PREF. Set the gain factor to the required value. If no extra gain is
required, set the
AMUX SELECTION
to
PHOTO AMPLIFIER
.
It is recommended to install a 470 k
Ω
resistor connecting PREF to VINT if the photo gain is set to 11x,
20x, or 35x. The 470 k
Ω
resistor changes the PREF voltage to 70mV and prevents the gain stage output
from dropping below 50mV in worst-case conditions.
