DM00113044

DM00113044
DT0017
Design tip
VL6180X interleaved mode explanation
By Colin Ramrattan
Main components
VL6180X
Proximity and ambient light sensing (ALS) module
Purpose and benefits
The purpose of this document is to explain in further detail the interleaved feature of the
VL6180X.
It is assumed that customers who use this document can communicate with the VL6180X
2
through I C and are now looking for more information on the interleaved operation mode.
Figure 1. VL6180X device
Description
Interleaved mode is a term used to describe a continuous mode of operation in the
VL6180X where the Ambient Light Sensor (ALS) and Ranging functions continuously
perform measurements over a user specified period. This operation is beneficial to users
that would like to have continuous measurements from both the ALS and range functions of
the VL6180X.
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Figure 2 below shows a timeline of how the ALS and ranging are executed when
interleaved mode is enabled.
Figure 2. ALS and ranging timeline
ALS Inter-Measurement Period
ALS Inter-Measurement Period
ALS Measurement
Continuous Mode
Range measurement
occurs automatically
after ALS measurement.
Range Measurement
Any Mode
HOST Interrupt
Enabling Interleaved Mode:
The following registers in Table 1 are used in interleaved operation.
Table 1.
Overview of registers to set using interleaved operation
Register Name
Register
Address
Description
SYSALS_
INTERMEASUREMENT_PERIOD
0x03E
This will define the time between the ALS measurements. Note: The
host must ensure that the inter-measurement time is not exceeded See
Table XXX.
SYSALS_INTEGRATION_PERIOD
0x040
The integration period is the time the ALS will integrate based on the
current light conditions. This is chosen by the user.
SYSALS_START
0x038
This register is used to select continuous mode operation for the ALS
measurements. If the interleaved mode enable bit is set, a range
measurement will be performed after each ALS measurement
SYSRANGE_MAX_
CONVERGENCE_TIME
0x01C
This will define the maximum time allowed for a range measurement to
complete. Note: The maximum time set cannot be more than the ALS
inter-measurement period.
SYSRANGE_START
0x018
This register is used to select either continuous or single shot range
measurements. Note: in interleaved mode, this register is ignored.
INTERLEAVED_MODE_ENABLED
0x2A3
To enable interleaved mode, this register must be set to 0x01.
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The following registers shown in Table 1 are a subset of what is used in normal operation
of the VL6180X. The user is advised to refer to the datasheet for further information on how
to set-up GPIO modes, interrupt conditions and other functions of the VL6180X.
To set-up interleaved mode, the user should decide the rate at which the device will report
ALS and range measurements. Once the time is chosen, the user must ensure this time
does not violate the following equations for proper operation.
ALS_Inter-Measurement period (ALS_IMP)
ALS_IMP > [(1.1 * ALS_INTEGRATION_PERIOD) +
(RANGE_MAX_CONVERGENCE_TIME + 5ms)] / 0.9
The equation above will ensure the system will have enough time to process each
measurement while continuing to report the appropriate measurements for ranging and
ALS.
Table 2 below shows an example of 10Hz operation along with the maximum permissible
settings for 10Hz operation. The ALS Integration period and max convergence time should
not be increased further but can be reduced from the example below.
Table 2. 10Hz interleaved operation example
Parameter Name
Time Required
Inter-measurement period
100ms
ALS Integration period
50ms
Range Max convergence time
30ms
Register address and value to write.
Address (0x03E), write value 0x0A
Address (0x040), write value 0x32
Address (0x01C), write value 0x1E
Table 3 below shows an example of 20Hz operation along with the maximum permissible
settings for 10Hz operation. The ALS Integration period and max convergence time should
not be increased further but can be reduced from the example below.
Table 3. 20Hz interleaved operation example
Parameter Name
Time Required
Inter-measurement period
50ms
ALS Integration period
20ms
Range Max convergence time
18ms
Register address and value to write.
Address (0x03E), write value 0x05
Address (0x040), write value 0x14
Address (0x01C), write value 0x12
For completeness, Table 3 below shows the user where the settings for interleaved
operation should be applied. Note that this is just a subset of what is required for normal
operation and the user is advised to refer to the datasheet for additional functions with the
VL6180X.
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Figure 3. Interleaved operation register writes flow
GPIO0 set to logic high to turn on device
Wait for device boot. User can wait at least 2ms or check register 0x016
for reset value of 0x01
Change I2C address if needed. (Optional)
Apply latest initialization tuning settings supplied by regional support
Apply VL6180X attributes ie. crosstalk, threshold, SNR
Set Interleaved operation register. Measurements are started after ALS
has been set to continuous mode and start bit is set in register 0x038
Read interrupts from VL6180X.
Support material
Related design support material
MOB-EK2-180-01/1
Product/ system evaluation board
Documentation
Datasheet: VL6180X - Proximity and ambient light sensing (ALS) module
Revision history
Date
27-MAY-2014
June 2014
Version
1
Changes
Initial release
DT0017 Rev 1
4/5
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