Texas Instruments TPS8804EVM User manual

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User's Guide
SLVUBT6A–October 2019–Revised May 2020
Using the TPS8804EVM
1 Introduction
The TPS8804EVM is used to evaluate the TPS8804 smoke and CO detector analog front end (AFE) and
power management IC. The EVM allows for easy connection from the TPS8804 to a user-supplied
photoelectric chamber and carbon monoxide sensor. The TPS8804 GUI interfaces with the EVM to quickly
evaluate the photo amplifier, LED driver, and CO amplifier performance, and other blocks with the register
map. For a more thorough evaluation, an external microcontroller can be connected to the TPS8804EVM
to create a smoke detection system.
1.1 Applications
• Smoke and CO detectors
1.2 Features
• Dual LED drivers for blue and IR LEDs
• Wide bandwidth, low offset photodiode amplifier
• Ultra-low power CO transimpedance amplifier
• LDOs for internal analog blocks and external microcontroller
• Single buffered analog output AMUX for CO and photo signals
• Serial interface for configuring amplifiers, drivers, regulators
• SLC interface for power line communication
• Under-voltage, over-temperature fault monitors
• Wide input voltage range for flexible power supply configuration
1.3 Recommended Equipment
• 4.5-V to 15.5-V power supply capable of 100mA
• USB2ANY™ interface adaptor
• TPS880x GUI software
– Installation files are available in the TPS8804EVM product folder
• Multimeter for measuring regulator voltages and CO amplifier output
• Oscilloscope for measuring photodiode signal pulse shape
2 Setup
Specific connections on the TPS8804EVM board require configuration before starting the evaluation.
2.1 Sensor Connections
TI recommends connecting a photoelectric smoke chamber and CO sensor to the TPS8804EVM for the
evaluation. The TPS8804EVM has a built-in photodiode (D7), blue LED (D8), and IR LED (D6) for
functional testing. These components can be de-soldered in order to connect a photoelectric chamber
photodiode, IR LED, and/or blue LED its place. Ensure the photodiode wires are kept short to preserve
signal integrity.

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The CO sensor is connected to J17 screw terminals with the sensor counter terminal tied to AGND.
2.2 Jumper and Switch Configurations
The S1 switch position determines the VMCU voltage at power-up. Ensure that only one S1 sub-switch is
in the ON position. Table 1 displays the VMCU voltage corresponding with each S1 switch position. For
proper operation with the USB2ANY adapter, set VMCU to 3.3 V with sub-switch 4.
Table 1. VMCU Power-up Voltage
S1 Switch Position VMCU
1 1.5V
2 1.8V
3 2.5V
4 3.3V
The J2 jumper connects VSLC to VCC. A single supply connected to VCC powers the entire EVM with the
jumper connected.
The J6 jumper selects the I2C device address. Connect J6 to the AGND position to set the address to
0x3F. Connect J6 to the VMCU position to set the address to 0x2A. The GUI is compatible with both
options and defaults to 0x2A.

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Figure 1. Switch, Jumper, and Power Connections
2.3 Power Connection
Connect the power supply to VCC and PGND. Set the power supply to 5 V, 100 mA. Enable the power
supply and measure the voltage on VMCU (TP27) to ensure it is operating at the voltage option selected
by S1:
• 1.5 V
• 1.8 V
• 2.5 V
• 3.3 V
See Table 1 for more information on the initial VMCU voltage.

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2.4 USB2ANY Connection
Use a USB cable to connect the USB2ANY adapter to a computer with the TPS880x GUI installed. Open
the TPS880x GUI and verify the USB2ANY adapter is recognized (see Figure 2). With the EVM powered,
connect the USB2ANY adapter to the EVM using the USB2ANY adapter 10-pin ribbon cable. Click
EXPLORE TPS8804EVM then QUICK START and select the device address corresponding to the J6
jumper (see Section 2.2). Send the test command to verify the EVM, USB2ANY adapter, and GUI
software are all connected.
Figure 2. TPS880x GUI Connected to USB2ANY Adapter

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Figure 3. Test Command Successful
3 Analog Evaluation
Click START EVALUATION and select the feature to evaluate. The Analog Front End section guides the
CO AFE and photo AFE evaluation. Enter the register map to evaluate the other blocks in the TPS8804
device.

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Figure 4. Evaluation Selection Menu
3.1 CO AFE Evaluation
If a CO sensor is available, connect it to the J17 terminal block. Select the feedback resistance and
reference voltage in the GUI software. The TPS8804EVM default configuration uses the internal resistors
and references. To use an external feedback resistor, solder a resistor to R5. To use an external input
resistor, replace the R1 0-Ωresistor with the required input resistance. The output resistor filters the CO
amplifier output when a capacitor is installed on C3.
Set the AMUX SELECTION to CO AMPLIFIER. Enable the CO amplifier and measure the voltage on
AMUX_BUF.

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Figure 5. CO Amplifier Settings
Figure 6. Clean Air CO Amplifier Output

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Figure 7. CO Amplifier Output with Sensor and Calibration Gas
3.1.1 CO Connectivity Test
A simple test confirms that the CO sensor is connected to the EVM. Remove the shunt connected to J7
and connect a shunt to J15 and J16. Write COTEST_EN = 1 and measure the pulse shape on
AMUX_BUF using an oscilloscope. When COTEST_EN = 1, the PREF pin is pulled low and injects charge
into the CO sensor and amplifier. The AMUX pulse shape is different if the CO sensor is disconnected.
Write COTEST_EN = 0, remove the J15 and J16 shunts, and connect the J7 shunt when finished.

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Figure 8. COTEST_EN Register Bit

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Figure 9. CO Connectivity Test without Sensor

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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 kΩresistor connecting PREF to VINT if the photo gain is set to 11x,
20x, or 35x. The 470 kΩresistor changes the PREF voltage to 70mV and prevents the gain stage output
from dropping below 50mV in worst-case conditions.

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Figure 11. Photo Amplifier Settings
Configure the power to the LEDs. By default, LED A and LED B are connected to LEDLDO. Use the J1,
J5, J8, and J14 jumpers to select which supply powers each LED. Enable the LEDLDO if it powers either
LED.

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Figure 12. LED Power Supply Settings
Configure the PWM pulse settings for the LED driver. The default setting 201 ms pulse rate and 1 ms
pulse width sufficiently tests the LED driver. This setting controls the PWM signal from the USB2ANY
adapter to the EVM.
Configure the LED current for each driver. The default EVM CSA resistance is 10 Ωand the default EVM
CSB resistance is 1.3 Ω. These resistors can be switched on the EVM to change the LED current and
temperature compensation. Set the DAC voltage to fine tune the LED current. Set the temperature
coefficient to the required setting. Click SETUP TEST after configuring the photo amplifier, LED power
supply, and LED driver.

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Figure 13. LED Driver Settings
Select the LED to be tested. Enable the LED PWM to send the PWM signal to the LEDEN pin. Enable
LEDPIN_EN to control the LED driver using the LEDEN pin. Place a box over the EVM if the EVM LEDs
and photodiode are used to block ambient light and reflect the LED light into the photodiode.
Use an oscilloscope to measure the LED current, photo input amplifier, and photo gain amplifier signals.
Probe LEDEN to measure the LED control signal. Probe CSA or CSB to measure the LED driver current.
Probe PDO to measure the photo input stage amplifier. Probe AMUX_BUF to measure the photo gain
stage amplifier.

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Figure 14. EVM Photo Measurement Probe Configuration

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Figure 15. LED A Signals

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Figure 16. LED B Signals

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Figure 17. Photo Signal with Photo Chamber
3.3 Register Map
Use the register map to evaluate other blocks in the TPS8804. Use the search to find register bits that
correspond to a certain block or function. Load and save register map configurations in the File menu.
Click the question mark icon (?) to display more information about the selected register or bits.

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Figure 18. Register Map Search Function

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4 Board Layout
Figure 19. TPS8804EVM Top Layer PCB Layout