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AD5543BR датащи(PDF) 9 Page - Analog Devices |
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AD5543BR датащи(HTML) 9 Page - Analog Devices |
9 / 12 page REV. A AD5543/AD5553 –9– Programmable Current Source Figure 10 shows a versatile V-I conversion circuit using an improved Howland Current Pump. In addition to the precision current conversion it provides, this circuit enables a bidirec- tional current flow and high voltage compliance. This circuit can be used in 4 to 20 mA current transmitters with up to 500 Ω of load. In Figure 10, it can be shown that if the resistor network is matched, the load current is: I RR R R VD L REF = + () ×× 23 1 3 / (5) R3 in theory can be made small to achieve the current needed within the U3 output current driving capability. This circuit is versatile such that AD8510 can deliver ±20 mA in both direc- tions and the voltage compliance approaches 15 V, which is limited mainly by the supply voltages of U3. However, users must pay attention to the compensation. Without C1, it can be shown that the output impedance becomes: Z RR R R RR R R R R O = + () + () + () 13 1 2 12 3 1 2 3 ' '' – ' (6) If the resistors are perfectly matched, ZO is infinite, which is desirable, and behaves as an ideal current source. On the other hand, if they are not matched, ZO can be either positive or nega- tive. Negative can cause oscillation. As a result, C1 is needed to prevent the oscillation. For critical applications, C1 could be found empirically, but typically falls in the range of few pF. VREF VDD U2 U1 AD5543/AD5553 VL GND IOUT RFB AD8628 AD8510 V+ V– VREF LOAD U3 VDD VSS R3 50 IL VDD C1 10pF R3' 50 R2 15k R1 150k R2' 15k R1' 150k Figure 10. Programmable Current Source with Bidirec- tional Current Control and High Voltage Compliance Capabilities |
Аналогичный номер детали - AD5543BR |
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Аналогичное описание - AD5543BR |
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