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ADN2847 Fiches technique(PDF) 11 Page - Analog Devices |
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ADN2847 Fiches technique(HTML) 11 Page - Analog Devices |
11 / 16 page Data Sheet ADN2847 Rev. B | Page 11 of 16 AD9850/AD9851 AD9834 DDS 50Ω IOUT 1.25mA TO 20mA IOUT 50Ω RSET CONTROLLER 37.5µA TO 600µA LP FILTER (DC-COUPLED) 500Ω BC550 0.125mA TO 2mA 10kHz TO 1MHz IDTONE ADN2847 35 32 IMMON 50µA TO 800µA 1kΩ 1/2 AD8602 BC550 1.3kΩ 1/2 AD8602 CLKIN REF CLOCK 20MHz TO 180MHz 9 21 20 12 Figure 12. Application Circuit to Allow Fiber Identification Using the AD9850/AD9851 ALARM INTERFACES The FAIL and DEGRADE outputs have an internal pull-up resistor of 30 kΩ, used to pull the digital high value to VCC. However, the alarm can be overdriven with an external resistor allowing alarm interfacing to non-VCC levels. Non-VCC alarm output levels must be below the VCC used for the ADN2847. POWER CONSUMPTION The ADN2847 die temperature must be kept below 125°C. Both LFCSP packages have an exposed paddle that should be connected in such a manner that is at the same potential as the ADN2847 ground pins. The θJA for both packages is specified in the Absolute Maximum Ratings section. Power consumption can be calculated using ICC = ICCMIN + 0.3 IMOD P = VCC × ICC + (IBIAS × VBIAS_PIN) + IMOD (VMODP_PIN+ VMODN_PIN)/2 TDIE = TAMBIENT +θJA × P Thus, the maximum combination of IBIAS + IMOD must be calculated, where: ICCMIN = 50 mA (typical value of ICC provided in the Specifications section) IBIAS = IMOD = 0 TDIE = die temperature TAMBIENT = ambient temperature VBIAS_PIN = voltage at IBIAS pin VMODP_PIN = average voltage at IMODP pin VMODN_PIN = average voltage at IMODN pin LASER DIODE INTERFACING Many laser diodes designed for 2.5 Gbps operation are packaged with an internal resistor to bring the effective impedance up to 25 Ω to minimize transmission line effects. In high current applications, the voltage drop across this resistor combined with the laser diode forward voltage makes direct connection between the laser and the driver impractical in a 3 V system. AC coupling the driver to the laser diode removes this headroom constraint. Caution must be taken when choosing component values for ac coupling (see Figure 15) to ensure that the time constants (L/R and RC) are sufficiently long for the data rate and expected number of consecutive identical digits (CIDs). Failure to do this can lead to pattern dependent jitter and vertical eye closure. For designs with low series resistance, or where external components become impractical, the ADN2847 supports direct connection to the laser diode (see Figure 14). In this case, care must be taken to ensure that the voltage drop across the laser diode does not violate the minimum compliance voltage on the IMODP pin. OPTICAL SUPERVISOR The PSET and ERSET potentiometers can be replaced with a dual-digital potentiometer, the ADN2850 (see Figure 13). The ADN2850 provides an accurate digital control for the average optical power and extinction ratio and ensures excellent stability over temperature. ADN2847 PSET ERSET DATAP DATAN IDTONE IMODP IBIAS IMPD ADN2850 DAC1 DAC2 SDI SDO CLK Tx Rx CLK CS VCC VCC VCC VCC RZ CS Figure 13. Application Using the ADN2850 a Dual 10-Bit Digital Potentiometer with an Extremely Low Temperature Coefficient as an Optical Supervisor |
Numéro de pièce similaire - ADN2847_15 |
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Description similaire - ADN2847_15 |
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