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ISL29020IROZ-EVALZ データシート(PDF) 7 Page - Intersil Corporation |
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ISL29020IROZ-EVALZ データシート(HTML) 7 Page - Intersil Corporation |
7 / 11 page 7 FN6505.0 September 26, 2008 INTEGRATION TIME IN EXTERNAL TIMING MODE The External Timing Mode is recommended when the integration time is needed to synchronize to an external signal, such as a PWM to eliminate noise. The synchronization can be implemented by using I2C sync command. The 1st I2C sync command starts the conversion. The 2nd completes the conversion then starts over again to commence the next conversion. The integration time, tint, is the time interval between the two sync pulses: where Timer is the number of internal clock cycles obtained from data registers and fOSC is the internal oscillator frequency. The internal oscillator, fOSC, operates identically in both the internal and external timing modes. However, in External Timing Mode, the number of clock cycles per integration is no longer fixed at 2n. The number of clock cycles varies with the chosen integration time, and is limited to 216 = 65,536. In order to avoid erroneous readings the integration time must be short enough not to allow an overflow in the counter register. Noise Rejection In general, integrating type ADCs 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. Optical Design Flat Window Lens Design A window lens will surely limit the viewing angle of the ISL29020. The window lens should be placed directly on top of the device. The thickness of the lens should be kept at minimum to minimize loss of power due to reflection and also to minimize loss due to absorption of energy in the plastic material. A thickness of t = 1mm is recommended for a window lens design. The bigger the diameter of the window lens, the wider the viewing angle is of the ISL29020. Table 11 shows the recommended dimensions of the optical window to ensure both 35° and 45° viewing angle. These dimensions are based on a window lens thickness of 1.0mm and a refractive index of 1.59. Window with Light Guide Design If a smaller window is desired while maintaining a wide effective viewing angle of the ISL29020, a cylindrical piece of transparent plastic is needed to trap the light and then focus and guide the light onto the device. Hence, the name light guide or also known as light pipe. The pipe should be placed directly on top of the device with a distance of D1 = 0.5mm to achieve peak performance. The light pipe should have minimum of 1.5mm in diameter to ensure that whole area of the sensor will be exposed. See Figure 5. TABLE 10. INTEGRATION TIME OF n-BIT ADC REXT (k Ω) n = 16-BIT n = 12-BIT n = 8-BIT n = 4-BIT 250 50ms 3.2ms 200µs 12.5µs 500** 100ms 6.25ms 390µs 24µs 1000 200ms 12.5ms 782µs 49µs 1500 300ms 18.8ms 1.17ms 73µs 2000 400ms 25ms 1.56ms 98µs **Recommended REXT resistor value t int Timer f OSC ----------------- = (EQ. 8) t int 65,535 f OSC ------------------ < (EQ. 9) TABLE 11. RECOMMENDED DIMENSIONS FOR A FLAT WINDOW DESIGN DTOTAL D1 DLENS @ 35° VIEWING ANGLE DLENS @ 45° VIEWING ANGLE 1.5 0.50 2.25 3.75 2.0 1.00 3.00 4.75 2.5 1.50 3.75 5.75 3.0 2.00 4.30 6.75 3.5 2.50 5.00 7.75 t = 1 Thickness of lens D1 Distance between ISL29020 and inner edge of lens DLENS Diameter of lens DTOTAL Distance constraint between the ISL29020 and lens outer edge * All dimensions are in mm. DLENS ∅ t D1 DTOTAL ∅ = VIEWING ANGLE WINDOW LENS ISL29020 FIGURE 4. FLAT WINDOW LENS E = DATA 216 x 1000 ISL29020 |
同様の部品番号 - ISL29020IROZ-EVALZ |
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同様の説明 - ISL29020IROZ-EVALZ |
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