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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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ISL29501-CS-EVKIT1Z Fiches technique(PDF) 10 Page - Intersil Corporation |
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ISL29501-CS-EVKIT1Z Fiches technique(HTML) 10 Page - Intersil Corporation |
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10 / 23 page  ISL29501 10 FN8681.3 June 29, 2016 Submit Document Feedback Emitter Driver Integrated in the ISL29501 is an emitter driver circuit. It is a current source designed to drive either the IR LED or laser. The circuit is enhanced to provide fast turn-on and turn-off of either LED or lasers. The driver needs about 1V of headroom to operate properly. It will still operate with lower voltages but the driver becomes less linear the lower you go. Headroom is defined as the voltage across the driver EVDD - Vforward emitter. This may limit the optical power of certain lasers. EIR Pin Figure 5 shows a simplified block diagram of the emitter driver. The circuit consists of two primary current DACs, main and threshold DAC. The EIR pin is connected to the emitter anode while the cathode is tied to ground (EVSS). The drive current is derived from a combination of a range (0x90) and value (0x91) DACs allowing a wide range of values. Main DAC The main DAC is implemented in two separate DACs. Combined they are designed to output a maximum current of 255mA of switched (pulsed) current. The current value is set by programming Registers 0x90 and 0x91. Register 0x90 is the range control and Register 0x91 for fine control. Depending on the application’s desired range and the type of emitter employed, the current level can be set to give the best SNR performance. The system designer will have to determine this value based on component selection. In addition, this fine tuning allows the application to compensate for production variation in the external components. The emitter current is governed by the following formula: IRDR = 0x90[3:0]/15*0x91[7:0]/255*255mA Threshold DAC In addition to the main DAC there is a threshold DAC that can provide DC current to the emitter. This might be useful in some laser applications by raising the off current to just below its threshold. The threshold current is active only during integration time to limit power consumption. Threshold current is not needed in most applications. A maximum of 30mA can be driven by the threshold DAC. The current is programmed in Register 0x93. The detailed description can be found in the “Register Map” on page 17. Connecting the Photodiode The photodiode should be connected between the PDn and PDp pins as shown in Figure 7. The photodiode operates in photoconductive mode, the voltages at PDp and PDn nodes are listed in the AFE specifications. The photodiode is reversed biased with anode at 0.7V and the cathode at 1.7V (1V reverse bias). Biasing the diode in photoconductive mode enables lower effective capacitance/faster operation and efficient collection of photo energy. Selecting the Photodiode This section provides general guidelines for the selection of the photodiode for receiver. Three key parameters that must be considered: 1. Peak wavelength 2. Collected light 3. Rise/fall time A detector with narrow band sensitivity in the NIR or MWIR are best for proximity sensing as most ambient light will be naturally rejected. The ideal PD would be a narrow band pass that is centered on the emitter peak wavelength. Diodes with no filter offer poor performance and should not be considered. We have to ensure that the emitter peak wavelength is aligned with the detector wavelength to achieve high SNR. Maximizing the collected light can be achieved with the largest active area the mechanical constraints allow or through the use FIGURE 5. EMITTER CONNECTIVITY 0x90[0:3] 0x91[0:7] EVCC EIR EVSS FIGURE 6. TYPICAL EMITTER WAVEFORM AND FEATURES FIGURE 7. CONNECTING PD TO AFE IRDR(mA) THRESHOLD DC 4.5MHz SQUARE WAVE AMPLITUDE TIME (s) PDn PDp Vbp = 0.7V Vbn = 1.7V DC CORRECTION AVSS AVDD GAIN + + - - |
Numéro de pièce similaire - ISL29501-CS-EVKIT1Z |
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Description similaire - ISL29501-CS-EVKIT1Z |
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