SBOS745A May 2016 – June 2016 OPT3002
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
There are two categories of interface to the OPT3002: electrical and optical.
The electrical interface is quite simple and is accomplished by connecting the OPT3002 I2C SDA and SCL pins to the same pins of an applications processor, microcontroller, or other digital processor. If that digital processor requires an interrupt resulting from an event of interest from the OPT3002, then connect the INT pin to either an interrupt or general-purpose I/O pin of the processor. There are multiple uses for this interrupt, including signaling the system to wake up from low-power mode, processing other tasks when waiting for an ambient light event of interest, or alerting the processor that a sample is ready to be read. Connect pullup resistors between a power supply appropriate for digital communication and the SDA and SCL pins (because they have open-drain output structures). If the INT pin is used, connect a pullup resistor to the INT pin. A typical value for these pullup resistors is 10 kΩ. The resistor choice can be optimized in conjunction to the bus capacitance to balance the system speed, power, noise immunity, and other requirements.
The power supply and grounding considerations are discussed in the Power-Supply Recommendations section.
Although spike suppression is integrated in the SDA and SCL pin circuits, use proper layout practices to minimize the amount of coupling into the communication lines. One possible introduction of noise occurs from capacitively coupling signal edges between the two communication lines themselves. Another possible noise introduction comes from other switching noise sources present in the system, especially for long communication lines. In noisy environments, shield communication lines to reduce the possibility of unintended noise coupling into the digital I/O lines that can be incorrectly interpreted.
The optical interface is physically located within the package, facing away from the printed circuit board (PCB), as specified by the Sensor Area in Figure 26.
Physical components, such as a plastic housing and a window that allows light from outside of the design to illuminate the sensor, can help protect the OPT3002 and neighboring circuitry. Sometimes, a dark or opaque window is used to further enhance the visual appeal of the design by hiding the sensor from view. This window material is typically transparent plastic or glass.
Any physical component that affects the light that illuminates the sensing area of a light sensor also affects the performance of that light sensor. Therefore, for optimal performance, make sure to understand and control the effect of these components. If a window is to be used, design its width and height to permit light from a sufficient field of view to illuminate the sensor. For best performance for non-collimated light, use a field of view of at least ±35°, or ideally ±45° or more. Understanding and designing the field of view is discussed further in the OPT3001: Ambient Light Sensor Application Guide application report.
Light pipes can appear attractive for aiding in the optomechanical design that brings light to the sensor; however, do not use light pipes with any ambient light sensor unless the system designer fully understands the ramifications of the optical physics of light pipes within the full context of the design and the design objectives.
For best results, illuminate the sensor area uniformly.
If the input wavelength is known and compensation for the nominal spectral response of the device is desired, apply Equation 4.
For example, if the input wavelength is 700 nm, then Figure 2 illustrates that the relative response is 0.6. Building on an example from Table 9, if the OPT3002 result register is E[3:0] = 03h and R[11:0] = 456h, then the optical power for light at a 505-nm wavelength is 338,2287 nW/cm2. Equation 5 demonstrates the correction for a 700-nm input. Note that this simple technique only works for a single wavelength input.
As with any optical product, special care must be taken into consideration when handling the OPT3002. Although the OPT3002 has low sensitivity to dust and scratches, proper optical device handling procedures are still recommended.
The optical surface of the device must be kept clean for optimal performance in both prototyping with the device and mass production manufacturing procedures. Tweezers with plastic or rubber contact surfaces are recommended to avoid scratches on the optical surface. Avoid manipulation with metal tools when possible. The optical surface must be kept clean of fingerprints, dust, and other optical-inhibiting contaminants.
If the device optical surface requires cleaning, the use of de-ionized water or isopropyl alcohol is recommended. A few gentile brushes with a soft swab are appropriate. Avoid potentially abrasive cleaning and manipulating tools and excessive force that can scratch the optical surface.
If the OPT3002 performs less than optimally, inspect the optical surface for dirt, scratches, or other optical artifacts.