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AD8644ARU 数据表(PDF) 5 Page - Analog Devices |
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AD8644ARU 数据表(HTML) 5 Page - Analog Devices |
5 / 8 page AD8614/AD8644 –5– REV. 0 SUPPLY VOLTAGE – V 0 220 46 8 10 12 14 16 18 9 8 0 4 3 2 1 7 5 6 AV = 1 RL = 2k CL = 200pF TA = 25 C SR+ SR Figure 19. Slew Rate vs. Supply Voltage FREQUENCY – Hz 100 10 1 10 100 10k 1k VS = 5V TA = 25 C Figure 20. Voltage Noise Density vs. Frequency FREQUENCY – Hz 100 10 1 10 100 10k 1k VS = 18V TA = 25 C Figure 21. Voltage Noise Density vs. Frequency APPLICATIONS SECTION Theory of Operation The AD8614/AD8644 are processed using Analog Devices’ high voltage, high speed, complementary bipolar process—HV XFCB. This process includes trench isolated transistors that lower parasitic capacitance. Figure 22 shows a simplified schematic of the AD8614/AD8644. The input stage is rail-to-rail, consisting of two complementary differential pairs, one NPN pair and one PNP pair. The input stage is protected against avalanche breakdown by two back-to-back diodes. Each input has a 1.5 k Ω resistor that limits input current during over-voltage events and furnishes phase reversal protection if the inputs are exceeded. The two differential pairs are connected to a double-folded cascode. This is the stage in the amplifier with the most gain. The double folded cascode differentially feeds the output stage circuitry. Two complementary common emitter tran- sistors are used as the output stage. This allows the output to swing to within 125 mV from each rail with a 10 mA load. The gain of the output stage, and thus the open loop gain of the op amp, depends on the load resistance. VCC + 1.5k VEE VCC VOUT 1.5k VCC Figure 22. Simplified Schematic The AD8614/AD8644 have no built-in short circuit protection. The short circuit limit is a function of high current roll-off of the output stage transistors and the voltage drop over the resistor shown on the schematic at the output stage. The voltage over this resistor is clamped to one diode during short circuit voltage events. Output Short-Circuit Protection To achieve a wide bandwidth and high slew rate, the output of the AD8614/AD8644 is not short-circuit protected. Shorting the output directly to ground or to a supply rail may destroy the device. The typical maximum safe output current is 70 mA. In applications where some output current protection is needed, but not at the expense of reduced output voltage headroom, a low value resistor in series with the output can be used. This is shown in Figure 23. The resistor is connected within the feedback loop of the amplifier so that if VOUT is shorted to ground and VIN swings up to 18 V, the output current will not exceed 70 mA. For 18 V single supply applications, resistors less than 261 Ω are not recommended. |
类似零件编号 - AD8644ARU |
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类似说明 - AD8644ARU |
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