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ISL29023IROZ-EVALZ Datasheet(PDF) 7 Page - Intersil Corporation |
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ISL29023IROZ-EVALZ Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 11 page 7 FN6691.0 March 3, 2009 Integration and Conversion Time The ADC resolution and fOSC determine the integration time, tint. where n is the number of bits of resolution and n = 4, 8, 12 or 16. Therefore, 2n is the number of clock cycles. n can be programmed at the command register 01(hex) bits 3 and 2. External Scaling Resistor REXT for fOSC and Range The ISL29023 uses an external resistor REXT to fix its internal oscillator frequency fOSC and the light sensing range, Range. fOSC and Range are inversely proportional to REXT. For user simplicity, the proportionality constant is referenced to 499k Ω: Noise Rejection In general, integrating type ADC’s have excellent noise-rejection characteristics for periodic noise sources whose frequency is an integer multiple of the conversion rate. For instance, a 60Hz AC unwanted signal’s sum from 0ms to k*16.66ms (k = 1,2...ki) is zero. Similarly, setting the device’s integration time to be an integer multiple of the periodic noise signal, greatly improves the light sensor output signal in the presence of noise. ADC Output in IR Sensing The ISL29023’s ADC output codes, DATA, are directly proportional to the IR intensity received in the IR sensing. Here, EIR is the received IR intensity. The constant β changes with the spectrum of background IR noise, such as sunlight and incandescent light. The β also changes with the ADC’s range and resolution selections. Suggested PCB Footprint It is important that the users check the “Surface Mount Assembly Guidelines for Optical Dual FlatPack No Lead (ODFN) Package” before starting ODFN product board mounting. http://www.intersil.com/data/tb/TB477.pdf Layout Considerations The ISL29023 is relatively insensitive to layout. Like other I2C devices, it is intended to provide excellent performance even in significantly noisy environments. There are only a few considerations that will ensure best performance. Route the supply and I2C traces as far as possible from all sources of noise. Use two power-supply decoupling capacitors, 1µF and 0.1µF, placed close to the device. Typical Circuit A typical application for the ISL29023 is shown in Figure 3. The ISL29023’s I2C address is internally hardwired as 1000100. The device can be tied onto a system’s I2C bus together with other I2C compliant devices. Soldering Considerations Convection heating is recommended for reflow soldering; direct-infrared heating is not recommended. The plastic ODFN package does not require a custom reflow soldering profile, and is qualified to +260°C. A standard reflow soldering profile with a +260°C maximum is recommended. TABLE 8. INTEGRATION TIME OF n-BIT ADC REXT (k Ω) n = 16-BIT n = 12-BIT n = 8-BIT n = 4-BIT 250 45ms 2.8ms 176µs 11µs 499** 90ms 5.6ms 352µs 22µs **Recommended REXT resistor value tint 2 n 1 fOSC -------------- × 2 n REXT 725kHz 499k Ω × ---------------------------------------------- × == (EQ. 4) (EQ. 5) Range 499k Ω REXT ------------------ Range k () × = (EQ. 6) fOSC 499k Ω REXT ------------------ 725 × kHz = DATAIR β E IR × = (EQ. 7) ISL29023 |
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