[FAQ] OPT3101: PCB design and bringup

For design all details are covered in TI provided resources: https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/815766/faq-opt3101-what-are-the-resources-ti-provides-for-developing-with-opt3101?tisearch=e2e-sitesearch&keymatch=opt3101#

This includes

1. system design (optics selection, estimating range/accuracy, etc.) in the system design doc and system estimator tool listed in the linked FAQ
2. PCB design details in the system design doc and EVM user guide both containing example layout and schematics listed in the linked FAQ
3. Calibration in the SDK, configurator tool, and calibration documents also listed in the linked FAQ

Bringup

After receiving the assembled PCB and starting on step 3 above - the first 2 steps listed in the SDK are step 0 and step 1 for PCB bringup. This should be done first after verifying that the board powers up before attempting to calibrate the device to ensure the PCB design is optimal. Calibrating a suboptimal PCB will result in subpar performance and in some cases may result in unsuccessful calibration. The steps below match steps 0 and 1 in the SDK.

Step 0: First readings from device - check raw crosstalk

Follow the process outlined in the calibration doc to block emitter light from reaching the photodiode in order to measure the crosstalk level before calibration. One way to measure crosstalk on the EVM is to place at least 3-4 layers of thick black electrical tape over the photodiode as shown below in the blue circle. For thinner tape more layers may be needed. Ensure the tape blocks all light (IR light is not visible to naked eye). A NIR camera may help to ensure this. Make sure that the tape is pressed firmly down to completely block light from entering the photodiode. With the photodiode masked the crosstalk is the reported amplitude as can be seen in the GUI on the EVM or in the SDK output after running step 0.

On the EVM the uncalibrated crosstalk is between 100 and 200 codes typically and this is a low value that can be calibrated out. Higher values will be more sensitive to environmental changes and may merit additional extra calibration steps (see calibration docs for more details). Follow best practices outlined in the TI provided resources will ensure lowest crosstalk. 

Step 1: Simple calibration and testing

After ensuring PCB design is good, step 1 involves performing simple calibration for crosstalk and phase offset. At this stage the photodiode should be masked again and amplitude measured should be 10 or less codes indicating correct calibration. Phase offset calibration is also performed at this step. Now at this setup, but not before, the device will give meaningful distance measurements.

Subsequent steps and TI provided docs cover the other calibration steps required to ensure best performance.