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ISL29012 데이터시트(PDF) 3 Page - Intersil Corporation |
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ISL29012 데이터시트(HTML) 3 Page - Intersil Corporation |
3 / 15 page 3 FN6476.1 December 10, 2008 Principles of Operation Photodiodes The ISL29012 contains two photodiode arrays which convert light into current. One diode (D1) is sensitive to both visible and infrared light, while the other one (D2) is only sensitive to infrared light; see Figure 21. Using the infrared portion of the light as a baseline, the visible light can be extracted. The ambient light output is the difference between D1 and D2. The resultant ALS spectral response vs wavelength is shown in Figure 7 in the “Typical Performance Curves” on page 11. After light is converted to current during the light data process, the current output is converted to digital by a single built-in integrating type signed 15-bit Analog-to-Digital Converter (ADC). An I2C command reads the visible light intensity in counts. The converter is a charge-balancing integrating type signed 15-bit ADC. The chosen method for conversion is best for converting small current signals in the presence of an AC periodic noise. A 100ms integration time, for instance, highly rejects 50Hz and 60Hz power line noise simultaneously. See “Integration Time or Conversion Time” on page 7 and “Noise Rejection” on page 8. The built-in ADC offers user flexibility in integration time or conversion time. There are two timing modes: Internal Timing Mode and External Timing Mode. In Internal Timing Mode, integration time is determined by an internal dual speed oscillator (fOSC), and the n-bit (n = 4, 8, 12,16) counter inside the ADC. In External Timing Mode, integration time is determined by the time between two consecutive I2C External Timing Mode commands. See “External Timing Mode” on page 7. A good balancing act of integration time and resolution depending on the application is required for optimal results. The ADC has four I2C programmable range selects to dynamically accommodate various lighting conditions. For very dim conditions, the ADC can be configured at its lowest range. For very bright conditions, the ADC can be configured at its highest range. Interrupt Function The active low interrupt pin is an open drain pull-down configuration. The interrupt pin serves as an alarm or monitoring function to determine whether the ambient light exceeds the upper threshold or goes below the lower threshold. The user can also configure the persistency of the interrupt pin. This helps to avoid false triggers, such as noise or sudden spikes in ambient light conditions. An unexpected camera flash, for example, can be ignored by setting the persistency to 8 integration cycles. I2C Interface There are eight (8) 8-bit registers available inside the ISL29012. The command and control registers define the operation of the device. The command and control registers do not change until the registers are overwritten. There are two 8-bit registers that set the high and low interrupt thresholds. There are four 8-bit data Read Only registers. Two bytes for the sensor reading and another two bytes for the timer counts. The data registers contain the ADC's latest digital output, and the number of clock cycles in the previous integration period. The ISL29012’s I2C interface slave address is hardwired internally as 1000100. When 1000100x with x as R or W is sent after a START condition, this device compares the first 7 bits of this byte to its address and matches. Figure 1 shows a sample one-byte read. Figure 2 shows a sample one-byte write. Figure 3 shows a sync_I2C timing diagram sample for externally controlled integration time. The I2C bus master always drives the SCL (clock) line, while either the master or the slave can drive the SDA (data) line. Figure 2 shows a sample write. Every I2C transaction begins with the master asserting a start condition (SDA falling while SCL remains high). The following byte is driven by the master, and includes the slave address and read/write bit. The receiving device is responsible for pulling SDA low during the acknowledgement period. Every I2C transaction ends with the master asserting a stop condition (SDA rising while SCL remains high). For more information about the I2C standard, please consult the Phillips™ I2C specification documents. Pin Descriptions PIN NUMBER PIN NAME DESCRIPTION 1 VDD Positive supply; connect this pin to a regulated 2.5V to 3.3V supply. 2 GND Ground pin. The thermal pad is connected to the GND pin. 3 REXT External resistor pin for ADC reference; connect this pin to ground through a (nominal) 100k Ω resistor with 1% tolerance. 4INT Interrupt pin; LO for interrupt/alarming, open drain output. 5SCL I2C serial clock The I2C bus lines can be pulled above VDD, 5.5V max. 6SDA I2C serial data ISL29012 |
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