Device settings

AN4545

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DocID026571 Rev 1

6

Device settings

6.1

Performance tuning

Changing the settings in this section can affect the performance of the overall system.

6.1.1

Max convergence time

The SYSRANGE__MAX_CONVERGENCE_TIME {0x1c} register sets an upper limit for the

max convergence time. See Figure 10.

Figure 10. System timing diagram for a signal ranging measurement

The max convergence time is made up of the convergence time and sampling period. By

default the max convergence time is set to 49ms during device power-up.

Reducing the max convergence time will reduce the maximum time a measurement will be

allowed to complete and can reduce the power consumption when no target is present. We

recommend a value of 30ms for the max convergence time as a suitable starting point.

Note:

Reducing the max convergence time will reduce the distance the VL6180X is able to range

to.

Since the max convergence time controls maximum duration of each range measurement, it

effectively controls the minimum signal rate required by the VL6180X to complete a range

measurement.

During a range measurement, the signal from the return array is counted within the

convergence time window. The VL6180X will only report an valid range when a threshold of

15360 has been reached. The minimum signal rate required for convergence is therefore

related to the Max convergence time via the following equation.

The sampling period is set to 4.4ms by default.

If the return signal from a target is lower than the minimum signal rate then the VL6180X will

return a range output of 255 and a max convergence will be flagged.

Min signal rate [cps]

15360

Max Conv time [s]

Sampling period [s]

–

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