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AD215AY Scheda tecnica(PDF) 8 Page - Analog Devices |
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AD215AY Scheda tecnica(HTML) 8 Page - Analog Devices |
8 / 12 page AD215 REV. 0 –8– Compensating the Uncommitted Input Op Amp The open-loop gain and phase versus frequency for the uncom- mitted input op amp are given in Figure 14. These curves can be used to determine appropriate values for the feedback resis- tor (RF) and compensation capacitor (CF) to ensure frequency stability when reactive or nonlinear components are used. FREQUENCY – Hz 100k 100M 1M 10M 25 20 –25 15 10 5 0 –5 –10 –15 –20 PHASE GAIN 80 100 280 120 140 160 180 200 220 240 260 Figure 14. Open-Loop Gain and Frequency Response Inverting, Summing or Current Input Configuration Figure 14 shows how the AD215 can measure currents or sum currents or voltages. VS1 IN+ IN– FB IN COM OUT HI OUT LO PWR RTN COM TRIM OUTPUT FILTER, BUFFER AND TRIM CIRCUITRY 1 3 4 2 38 36 37 43 AD215 CF 47pF RF RS1 VS2 RS2 IS Figure 15. Noninverting Summing/Current Configuration For this circuit, the output voltage equation is: VO = –RF × (IS + VS1/RS1 + VS2/RS2 + . . .) where: V = Output Voltage (V) VS1 = Input Voltage Signal 1 (V) VS2 = Input Voltage Signal 2 (V) IS = Input Current Source (A) RF = Feedback Resistor ( Ω) (10 kΩ, typ) RS1 = Input Signal 1 Source Resistance ( Ω) RS2 = Input Signal 2 Source Resistance ( Ω) The circuit of Figure 15 can also be used when the input signal is larger than the ±10 V input range of the isolator. For example, in Figure 15, if only VS1, RS1 and RF were connected as shown with the solid lines, the input voltage span of VS1 could accom- modate up to ±50 V when R F = 10 k Ω and R S1 = 50 k Ω. GAIN AND OFFSET ADJUSTMENTS General Comments The AD215 features an output stage TRIM pin useful for zero- ing the output offset voltage through use of user supplied circuitry. When gain and offset adjustments are required, the actual com- pensation circuit ultimately used depends on the following: • The input configuration mode of the isolation amplifier (non- inverting or inverting). • The placement of any adjusting potentiometer (on the isolator’s input or output side). As a general rule: • Gain adjustments should be accomplished at the gain-setting resistor network at the isolator’s input. • To ensure stability in the gain adjustment, potentiometers should be located as close as possible to the isolator’s input and its impedance should be kept low. Adjustment ranges should also be kept to a minimum since their resolution and stability is dependent upon the actual potentiometers used. • Output adjustments may be necessary where adjusting poten- tiometers placed near the input would present a hazard to the user due to the presence of high common-mode voltages dur- ing the adjustment procedure. • It is recommended that input offset adjustments are made prior to gain adjustments. • The AD215 should be allowed to warm up for approximately 10 minutes before gain or offset adjustments are made. Input Gain Adjustments for Noninverting Mode Figure 16 shows a suggested noninverting gain adjustment cir- cuit. Note that the gain adjustment potentiometer RP is incorpo- rated into the gain-setting resistor network. RIN = 2kΩ VSIGNAL IN+ IN– FB IN COM OUT HI OUT LO PWR RTN COM TRIM OUTPUT FILTER, BUFFER AND TRIM CIRCUITRY 1 3 4 2 38 36 37 43 AD215 CF 0.47pF RF RG RC RP Figure 16. Gain Adjustment for Noninverting Configuration For a ±1% trim range: (RP ≈1kΩ), RC ≈ 0.02 × RG × RF RG + RF |
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