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AD9032 Arkusz danych(PDF) 6 Page - Analog Devices |
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AD9032 Arkusz danych(HTML) 6 Page - Analog Devices |
6 / 8 page AD9032 REV. 0 –6– USING THE AD9032 Layout Information Preserving the accuracy and dynamic performance of the AD9032 requires that designers pay special attention to the lay- out of the printed circuit board. Signal paths should be imped- ance matched and properly terminated at or near the package connections. Analog signal paths should be isolated from digital signal paths. Capacitive and inductive coupling of digital signals into analog signal sections can degrade the overall performance of the A/D converter. Analog Input The analog input pin of the AD9032 is terminated with a 100 Ω load. The analog input range of the AD9032 is factory trimmed for a ±1.024 V input for compatibility with the AD9034. The signal presented to the monolithic T/H is divided in half to opti- mize dynamic performance. When the amplitude, bandwidth, or dc level of the analog input requires external signal conditioning, the selection of the input amplifier is of particular concern. The noise and distortion of the amplifier must be taken into account to preserve the dy- namic range of the AD9032. The AD9617 wideband, current feedback amplifier is an excellent choice for most applications. Timing Internal timing for the AD9032 is trimmed at the factory to sim- plify use. Care should be taken to ensure that the encode com- mand to the AD9032 is free from jitter that can degrade dynamic performance. Differential ECL inputs to the AD9032 can be derived from a single-ended source using a fast compara- tor such as the AD96685. The encode source should be located and terminated as close to the AD9032 as possible. The ECL-compatible digital outputs are latched to provide valid data for the entire conversion period (less the transition region of latch). This data should be latched into external ECL regis- ters located near the AD9032. External termination resistors are required (510 Ω recommended). The data are latched with ei- ther the encode command or the data ready signal provided on the AD9032. The rising edge of the data ready signal occurs typically 7.5 ns after the data changes. Gain and Offset Adjustment Gain and offset pins are normally not connected. Rated perfor- mance is guaranteed without any external connection to these pins. In most applications, wide variations in input signal range and offset can be accommodated using external amplifiers. However, in those applications where a vernier adjustment is re- quired (such as nulling out factory trim limits), the gain and off- set pins will provide sufficient adjustment range. Both inputs offer a 20 k Ω input resistance that can be driven from a voltage source (DAC, amplifier) or the center tap of a potentiometer. The offset pin provides a 195 mV/V sensitivity to input offset, while the gain pin offers 120 mV/V adjustment of the full-scale input range of the ADC. The adjustment range for offset is limited to 10 mV and for gain is 20 mV without intro- ducing potential dynamic errors or restricting the operating tem- perature range of the part. Power Supplies The unique design of the AD9032 provides excellent dynamic performance without a need for high voltage power supplies. Two supplies (+5 V and –5.2 V) are all that are required to achieve rated performance. Careful layout and decoupling of power supplies used in conjunction with a low impedance ana- log ground plane will reduce supply-related noise components. Separate analog and digital supplies are not required. In applica- tions with only limited analog supply current, a separate digital supply source can be used for the –5.2 V supply on Pin 20. This supply typically requires 310 mA (330 mA max) and may be shared with other ECL logic devices when isolated with bypass capacitors and/or ferrite bead inductors (Fair-Rite Products Corporation part # 2743001111, Wallkill, NY). Each power supply pin should be capacitively decoupled to the ground plane through a good high frequency ceramic capacitor (0.1 µF) and a single large value capacitor (tantalum 10 µF). For optimum performance, “clean” linear supplies ensure that switching noise on the supplies does not introduce distortion products during the encoding process. Recognizing, however, that switching power supplies may be required in power- sensitive applications, decoupling recommendations outlined above are critically important for using switching supplies effectively. Elsewhere in this data sheet, a graph shows the PSRR of the AD9032 as a function of the ripple frequency present on the AD9032 supplies. Clearly, if they must be used, switching power supplies with the lowest possible frequency should be selected. Thermal Management The AD9032 design minimizes power dissipation; however, the ADC does typically require 3.8 W (4.5 W max) to operate. To ensure long life and reliable operation, the maximum junction temperature in the AD9032 must be limited to +175 °C. Within the hybrid, the hottest discrete die has a case to junction temperature rise of 10 °C (max). Therefore, the case tempera- ture of the AD9032 should not exceed +165 °C under worst case operating conditions. Without airflow, the θ CA of the hybrid package is 13 °C/W. Assuming maximum power dissipation, this causes a 57 °C rise in case temperature over the ambient air tem- perature. The maximum still air temperature, therefore, is equal to +108 °C. Rated performance of the AD9032 is guaranteed for case oper- ating temperatures of +85 °C (AD9032A/B) and +125°C (AD9032T). This equates to a maximum operating ambient temperature of +28 °C and +68°C, respectively, in still air. In most applications, airflow is recommended. The following im- provements in the thermal characteristics of the system assume that the AD9032 is soldered to a PC board. The θ CA of the hybrid is reduced to 5°C/W with 500 LFPM air- flow. This will extend the rated performance to ambient operat- ing ranges of +63 °C for the AD9032A/B and +103°C for the AD9032T. The addition of a heat sink (Thermalloy #6087B, Dallas, Texas; phone 214-243-0839) will further improve the thermal transfer of the hybrid to 3 °C/W (@ 500 LFPM). Using a heat sink with airflow, the total case to ambient temperature rise is only 13 °C, which results in a maximum ambient environ- ment of +72 °C (AD9032A/B) and +112°C (AD9032T). OBSOLETE |
Podobny numer części - AD9032_15 |
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Podobny opis - AD9032_15 |
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