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ISL29038IROZ-EVALZ Datasheet(PDF) 10 Page - Xicor Inc. |
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ISL29038IROZ-EVALZ Datasheet(HTML) 10 Page - Xicor Inc. |
10 / 15 page ISL29038 10 FN7851.0 October 12, 2012 Registers 0x01, 0x02 are used to configure the primary proximity and ALS parameters. Register 0x03 is used for optimizing IR compensation in ALS measurements. A procedure to optimize IR compensation is described in “ALS IR Compensation” on page 11. Register 0x04 is the Interrupt Configuration and Status Register, and is used primarily to indicate interrupt events from proximity and ALS measurements. A PWR_FAIL bit to indicate a ‘Brown-Out’ event is available and is set in case of a power supply interruption. A ‘Brown-Out’ event does not generate a hardware interrupt. The host micro-controller must clear this bit by writing a ‘0’ to Reg 0x04[4]. Register 0x04 is also used to configure ALS & Proximity interrupt persistency and the operation of the INT pin. Registers 0x05 and 0x06 are used to set the proximity ‘LOW’ and ‘HIGH’ threshold for proximity interrupt event generation. Registers 0x07, 0x08 and 0x09 are used to set the ALS ‘LOW’ and ‘HIGH’ threshold. Two 12-bit numbers span three address locations as shown in Table 1. Data registers 0x0A holds result of proximity conversion. The proximity result should be validated by ‘Washout’ bit in Reg 0x0D[0]. Registers 0x0B and 0x0C hold result of an ALS measurement. The ALS data is 12 bits wide. Least Significant Byte of the ALS data is available at address 0x0C and Most Significant Byte (MSB) of ALS data is available at address 0x0B. The MSB is right justified, i.e., the upper nibble is always zero and lower nibble contains four data bits. Register 0x0D[7:1] contains ambient IR measurement in proximity measurement phase. This measurement is for detecting ambient Washout condition, which is indicated by Reg 0x0D[0] being ‘HIGH’. Proximity ‘Washout’ is described in “Proximity Ambient Washout Detection” on page 11. A software reset can be initiated by writing 0x38 to Reg 0x0E. ISL29038 Operation Photodiodes and ADCs The ISL29038 contains two photodiode arrays, which convert photons (light) into current. The ALS photodiodes are designed to mimic the human eye’s wavelength response curve to visible light. The ALS photodiodes’ current output is digitized by a 12-bit ADC. The ALS ADC output is accessed by reading from Reg 0x0B and 0x0C when the ADC conversion is completed. The ALS ADC converter uses a charge-balancing architecture. Charge-balancing is best suited for converting small current signals in the presence of periodic AC noise. ISL29038 targets an integration time of 90ms, which can vary ±15% from nominal. The ALS integration time is intended to minimize 60Hz flicker. The proximity sensor uses an 8-bit ADC, which operates in a similar fashion. The IRDR pin drives (pulses) an infrared LED, the emitted IR reflects off an object back into the ISL29038, and the photo diodes convert the reflected IR to a current signal in 0.5ms. The ADC subtracts the IR reading before and after the LED is driven to remove ambient IR contribution. The ALS runs continuously with new data available every 90ms. The proximity sensor runs continuously with a time between conversions controlled by PROX_SLP (Reg 0x01[6:4]). Ambient Light Sensing The ISL29038 is set for ambient light sensing when Register bit ALS_EN = 1. Four measurement ranges from 125 Lux to 4000 Lux are available. The ALS measurement range is configured via Reg 0x02[1:0]. Proximity Sensing When proximity sensing is enabled (PROX_EN = 1), the external IR LED is driven for 100µs by the built-in IR LED driver through the IRDR pin. The IR LED current depends on PROX_DRV (Reg 0x01[1:0]). Drive current settings are as shown in Table 1. IR LED drive is in high impedance state when not active. When the IR from the LED reaches an object and gets reflected back to the ISL29038, the reflected IR light is converted into a current. This current is converted to digital data using an 8-bit ADC. The proximity measurement takes 0.5ms for one conversion including the 90μs LED drive time. The period between proximity measurements is determined by PROX_SLP (sleep time) in Reg 0x01[4:2]. Average LED driving current consumption is given by Equation 1. A typical IRDR scheme is 250mA pulses every 400ms, averaging about 56μA DC. Total Current Consumption Total current consumption is the sum of IDD and IIRDR. The IRDR pin sinks current and the average IRDR current is calculated using Equation 1. IDD depends on voltage and the mode-of-operation. For simplicity, Equation 1 ignores proximity ADC conversion time since it is much smaller than the sleep time. ALS ACTIVE 90ms 90ms 90ms PROX SENSOR ACTIVE IRDR (CURRENT DRIVER) ALS CONVERSION TIME = 90ms (FIXED) 0.50ms FOR PROX CONVERSION SERIES OF CURRENT PULSES TOTALING 0.09ms SLEEP TIME (PROX_SLP) 90ms 90ms SEVERAL µs BETWEEN CONVERSIONS TIME TIME TIME FIGURE 10. TIMING DIAGRAM FOR PROX/ALS EVENTS - NOT TO SCALE I lRDR AVE ; I lRDR PEAK ; 90 μs × T SLEEP ----------------------------------------------------- = (EQ. 1) |
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