UG055 Rev 0.00 Page 2 of 15
October 7, 2015
ISL29501-ST-EV1Z
Functional Description
The ISL29501-ST-EV1Z is both a reference design and
demonstration board that provides a single platform to
demonstrate the features of the ISL29501. The
ISL29501-ST-EV1Z circuit board and supplied enclosure have
been designed to deliver maximum electrical and optical
performance.
The system sends out light pulses through the emitter LED and
receives returned light pulses that reflected off a target. The
difference in phase of the emitted signal and the return signal is
converted to distance by the ISL29501 and is graphed in the
evaluation software. The magnitude of the return signal is
graphed as well. This and additional data is available in chip
registers, see UG054, “ISL29501 Evaluation Software User
Guide” for additional details.
Operating Features
The ISL29501-ST-EV1Z demonstration board is shown in
Figures 4 and 5. The hardware enable function is controlled by a
software switch, which can be overriden shorting J9 pins 1 and 2.
See the schematic for details. A Power-Good (PG) LED indicates
that the LDO is regulating properly.
External Power Supply
For high current/high duty cycle setups USB power may not be
able to power the board. In the default condition, jumper J10
shorts pins 1 and 2 to connect to USB power to the LDO. To power
the board with an external power supply, remove this jumper and
connect the positive (+) terminal to J10-2 and the negative (-) to
J10-4.
If you want to bypass the LDO and power the ISL29501 directly
with a power supply, remove the jumper on J10. Use J10-4 for
your ground connection and apply the positive voltage to TP7.
External Microprocessor
For debug of customer written software, it might be useful to
connect the Sand Tiger to a different microprocessor. The I2C
pins SCL and SDA are available on pins J4-4 and J4-3
respectively. The remaining support pins are available on
J5: SS - J5-4, IRQ - J5-3 and CEn - J5-2. The support pins are
generally connected to GP pins on the microprocessor. SCL and
SCL are compatible with 1.8V microprocessors but unfortunately
the support pins require 3V signaling.
System Calibration
Before meaningful measurements can be made the calibration
registers in the chip need to be loaded. This can be done in two
ways. The first is to load a profile that contains data into the GUI.
This could be one of the Intersil provided profiles or one that was
saved previously by the user. See UG054, “ISL29501 Evaluation
Software User Guide” for further details. The second is to
calibrate the board directly.
Calibrating Sand Tiger
There are 3 separate standard calibrations that need to be
executed in order to calibrate the system. These are magnitude,
crosstalk and distance calibrations.
MAGNITUDE CALIBRATION
Magnitude calibration is done after the emitter current and duty
cycle settings are programmed. It is a dark (no light) calibration
that takes less than 1s to run. Run this calibration from the GUI.
CROSSTALK CALIBRATION
Crosstalk is defined as a signal that reaches the ISL29501 chip
directly without bouncing off the target. This can be electrical or
optical. At close range and large return signal values, crosstalk
has a minor impact on distance measurements. At the far end of
the distance range the crosstalk might exceed the signal, adding
error to measurements.
For this calibration the user makes a distance measurement with
the return signal blocked from reaching the photodiode. This can
be done in two ways. The first is to cover the emitter or
photodiode optically preventing any of the emitted signal from
reaching the photodiode. The second is to point the board toward
infinity so there is no return signal. Care must be taken since
small amounts of signal will be returned by objects up to 4
meters away. The emitting angle of the light is ±3° so you must
be sure that there are no objects within this cone when doing this
calibration.
Since the chip sees none of the emitted signal anything received
is crosstalk. Run this calibration from the GUI after running
Magnitude calibration.
DISTANCE CALIBRATION
Variation in delay of emitters, photodiodes and the ISL29501 will
change the signal path delay. To compensate for this a reference
point at a known distance needs to be established. This
reference is calculated during distance calibration. The process
involves making a distance measurement at a known distance.
While it is not critical it is best to use a reference distance about
25% of the intended range. The GUI will write the correct
registers that establish the reference distance inside the chip.
It is important that there are no objects inside the ±3° emitting
angle other than the target.
Once these calibration registers are written, all succeeding
distance will have this value subtracted real time from the
measured value. Run this calibration from the GUI after running
crosstalk calibration. See UG054, “ISL29501 Evaluation
Software User Guide” for details on how to run the calibrations in
the GUI.
Operating Range
The circuit board contains an LDO to convert the input voltage to
the ISL29501 operating voltage range, 2.7V - 3.3V. By default the
board is configured for USB power but can be alternately
powered by an external power supply. The LDO resistors are
ratioed to create a 3.0V power rail. All other set-up conditions can
be configured through the chip registers and evaluation software.
