Application Note
ISL29501 Temperature and Ambient Light Data Collection

The ISL29501 has the ability to do real-time correction of distance measurements because of changing
temperature and ambient light conditions. To best serve our initial customers, Renesas createa correction
coefficients based on collected data taken in the end application. To make this process efficient, the data needs tobe delivered in a standardized format, which is described in this document.

Contents
1.

Advanced Calibration Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.

Collecting Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.

Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.

Advanced Calibration Process

The following are the required steps in the advanced calibration process.
1. Data is collected for phase while a single independent variable is changed. At this time, supported variabletypes are die temperature and ambient light. The ISL29501 has separate 8-bit registers for each of these.
Phase is collected along with the ISL29501 measured temperature or ambient light data.
2. At Renesas, a graph is made of phase versus the independent variable. A least squares curve fit to a 2nd orderpolynomial is generated from the data. The process involves creating an Excel trendline. The resultant curve
has the form of Ax2 + Bx + C. From the Excel curve the A and B coefficients are calculated and converted into
the correct hexadecimal format.
3. The values for A, B and an exponent are emailed back to the customer who programs them into the correct
registers. These values need to be programmed into the ISL29501 each time the chip is power cycled. They
can be left at the default (0x00), which does no correction.
4. The final constant C comes from the standard distance calibration. Distance calibration is the reference point
where all errors should be nulled. At the time of distance calibration a reference temperature needs to be written
into the chip. The user reads register 0xE2 and needs to write this result into 0x31. For high integration time
settings, the temperature changes while running the distance calibration routine. The best way to compensate
for this is to average the temperature value in the distance calibration routine and write the average into 0x31
at the end. For many circuit board designs, it is acceptable to read only a single temperature during the lastmeasurement in distance calibration.

2.

Collecting Data

Temperature and ambient light are two independent sweeps, these cannot be done at the same time. The user
should start from power-on conditions and then program the emitter current and integration time. Before collecting
data, all 3 standard calibrations should be performed or values loaded from a previous calibration. All registers
from 0x31 to 0x52 should be at the default (power-up) state of 0x00. Temperature should be varied in an oven so
the emitter and photodiode change along with the ISL29501 chip. A heat gun should not be used as it is unlikely toproduce a representative temperature gradient. A good technique is to ramp the temperature from the minimum tothe maximum over ~5 minutes recording 1 - 5 distance measurements per second. About 80% of temperature driftin caused by the photodiode. In an oven it is best to use a black target, ~10% to minimize the amount ofAN1967 Rev.1.00
Apr 11, 2022

Page 1© 2015-2022 Renesas Electronics

ISL29501 Temperature and Ambient Light Data Collection Application Notereflections inside the oven. The target should be sized and the board aligned so that beam completely strikes thetarget.
CSV is the required data format. The application software needs to output three registers separated by a comma.
The order is not important. The required registers are listed below:▪ Temperature - registers 0xE2, 0xD8, 0xD9
▪ Ambient Light - registers 0xE3, 0xD8, 0xD9
In all cases, the independent variable (temperature or ambient light) should be swept across the anticipated rangeof the application. A good target is a minimum of 10 measurement steps and at least 100 measurements made ateach step. More data points are better so that noise is averaged out.
In ambient light data sweeps, it is important that the temperature remains constant. If that cannot be guaranteed,
the temperature coefficients should be generated and programmed into the chip before collecting data in theambient sweep. To avoid self-heating of the board, use low integration times (reg0x10 ≤ 0x02) to avoid raising thedie temperature. The emitter (reg90 and reg91) should be programmed to the application condition. Bothcalibrations are independent and have separate coefficients. The user can choose to do either one or both or doone now and the other later. There is a single exponent that is shared by both sets of coefficients, which is also
provided.

3.

Revision History
RevisionDate

1.00

Apr 11, 2022

0.00

Oct 6, 2015

AN1967 Rev.1.00
Apr 11, 2022

Description
Applied New Template.
Added Revision History section.
Initial release.

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(Rev.1.0 Mar 2020)

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