VCSELs (the laser) is a odd thing. It works a lot better in the cold. And so we spend a lot of time paying attention to the temperature. In fact temperature - as you have seen - leads to the biggest variation in accuracy.
The VL6180 does have a temp sensor in it. That's how we do the VHV adjustment.
But unfortunately there is no read-out.
15mm seems quite high. But the datasheet does indicate you could get that much variation.
Do check to see that it's not condensation was getting on your coverglass and giving you a short answer? My guess is that it's not only the cold, but something physical that is giving you grief.
Clearly adding your own compensation would work.
Unfortunately I do not see a register to read out either the Temp or the VHV setting. Both of which might give you a clue as to how to do the correction.
A manual VHV calibration is performed by setting SYSRANGE__VHV_RECALBRATE{0x2E} to 1. This register auto-clears. This operation should only be performed in software standby. If temperature is really bugging you, you could set this for every range.
As an experiment, add a temp sensor and see if your compensation idea works. Use at least a couple of sensors from different lots.
That TI OP3101 chip is pretty good. But it only does the math. One still needs a VCSEL and an optical sensor to go with it.
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