VL6180x TOF Sensor VCSEL Continuity Test Error

[NPate.14]

On our prototype circuit boards with VL6180x sensors there are 6 sensors per board. On a couple of our prototype boards (about 10% of our boards) we have seen just a single sensor able to respond over I2C but cannot start ranging. The result range status register always reports a  result__range_error_code: 1 - VCSEL Continuity Test error. I2C communications are fine and all other 5 sensors are able to range.

What is this power up test doing and what could cause this error?

[John E KVAM]

It's a power issue.

The ToF chips from ST use 20mA when they are running. But that is an average during the 10ms or so it takes to get a range.

At the micro level the laser turns on and off at about a 30% duty cycle and during that 'on' the sensor draws quite a bit of power.

We believe this is your issue.

Bigger regulator perhaps?