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Toshiba Introduces Family of Photo IC Illumination Sensors for Mobile Applications
To Reduce Power Consumption and Increase Battery Life, Toshibaŭs Devices Detect Ambient Luminance that Controls the Backlight of the Display and Keypad
| The manufacturer says . . . | ChipCenter's Paul O'Shea says . . . |
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To address the increasing demand for more efficient power management features in mobile applications, Toshiba America Electronic Components, Inc. (TAEC)* today extended its family of photo integrated circuit (IC) illumination sensors with the addition of two new devices, designated the TPS850 and TPS851. Developed by Toshiba Corp. (Toshiba) the new photo-IC sensors are designed to reduce power consumption in highly-functional mobile applications such as cellular phones, personal digital assistants (PDAs), notebook PCs, camcorders and digital cameras which offer enhanced features such as color liquid crystal display (LCD) screens and keypad illumination. Because lighting situations can fluctuate based on the location of the application and the time of day, the backlighting of the LCD screen and keypad is not always required, particularly in well-lighted circumstances such as broad daylight or in brightly-lit indoor rooms. To address this concern, Toshibaŭs photo-IC illumination sensors are designed to automatically detect the level of ambient light to control the level of the backlighting required, thereby extending the battery life of the portable device. ŭDesigners of todayŭs mobile applications are consistently looking for ways to reduce power consumption and increase the battery life of their systems,ŭ said Masanobu Sato, business development manager for TAECŭs discrete products. ŭToshibaŭs illumination sensors not only meet the growing requirements for energy efficiency in these applications, but also offer system designers measurable space savings to meet the requirements for smaller designs.ŭ Housed in surface mount packages, Toshibaŭs TPS850 and TPS851 offer an integrated single-chip photodiode and amplifier circuit. These unique features, when coupled with the internal luminosity efficiency correction (LEC) function, enable engineers to design thinner devices, saving more than 30 percent of the board space when compared to other photo-detector solutions currently on the market, such as photo transistors with LEC glass filters. ŭExtending the battery life of power-hungry mobile applications is a continuous challenge for designers to overcome,ŭ said Dale Ford, director market intelligence services with iSuppli Corporation. ŭWith the ability to automatically adjust display backlighting as needed, illumination sensors help toward conserving battery life for more user-intensive applications.ŭ Toshibaŭs TPS850 and TPS851 photo-IC illumination sensors offer high sensitivity to light and can detect a light current (IL) ranging from 10 microampers (mA) to more than 10,000mA with corresponding luminance (lx) levels ranging from more than 10 to more than 2000. For example, when controlling the LCD and keypad backlighting function, the photo IC illumination sensor can sense the brightness required based on ambient luminance, forcing the backlight into power-save mode for levels exceeding 500 lx for the LCD screen and 200 lx for the keypad. |
The TPS850 and TPS851 illumination sensors are targeted at the mobile equipment market. These sensors will find a home in the power management designer's bag of tricks. For todayŭs mobile equipment there is a need for LCDs and backlighting that use power management techniques. Designers need a way to adjust backlighting according to ambient light conditions so power is not wasted and battery life is extended. This is important because LCDs consume a lot of power, especially color LCDs. The current solution on the market is typically a photo transistor. Unfortunately, photo transistors have sensitivity to infra red (IR) light so external luminous efficiency correction (LEC) filters are needed to correct the IR sensitivity. For example, in different light sources such as incandescent or fluorescent, the human eyes detect the same light levels because they canŭt detect IR light. However, phototransistors detect different light levels because they are sensitive to IR light. So thatŭs why you need an external LEC filter, and that requires mounting board space. The phototransistor also needs external components such as external amplifiers because of low sensitivity at low light. The TPS850/1 circuitry requires a resistor and capacitor but even with those parts this solution is still 30% thinner than the typical solution with an LEC filter. Phototransistors have a large distribution of light current making it difficult to adjust output current. The TPS850/1 incorporates the LEC filter and amplifier circuit in one chip, saving mounting space on the PCB. It also has high sensitivity at low light and has narrow distribution of light current, making it easy to adjust the output voltage. The TPS851 was developed in response to customers who wanted a smaller size illumination sensor. However, there is a small tradeoff in performance: the 850 offers higher sensitivity to light than the 851. The one you choose depends on your requirement for package size. Toshiba says the 851 is targeted for more compact equipment like mobile phones or digital cameras. Toshiba suggests that designers use the formula at the bottom of the block diagram, where output voltage, Vout, is calculated according to the formula: VOUT (V) = IL (A) x RL (ohms) ( VCC - 0.8V).
Vout can be adjusted by selecting a different RL. So if a designer requires a larger illumination detection area then they should use a smaller RL (illuminance resistor between Vout and ground). The following link shows a comparison of the illumination sensor to some competitive products. The graph shows luminance on the X axis and the light current on the Y axis, and provides a light sensitivity comparison.
Samples and production quantities of Toshibaŭs TPS850 and TPS851 photo-IC illumination sensors are available now. |
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