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AD5662ARJ-1REEL7 Datasheet(PDF) 19 Page - Analog Devices |
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AD5662ARJ-1REEL7 Datasheet(HTML) 19 Page - Analog Devices |
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19 / 24 page  AD5662 Rev. A | Page 19 of 24 BIPOLAR OPERATION USING THE AD5662 The AD5662 has been designed for single-supply operation, but a bipolar output range is also possible using the circuit in Figure 42. The circuit gives an output voltage range of ±5 V. Rail-to-rail operation at the amplifier output is achievable using an AD820 or an OP295 as the output amplifier. The output voltage for any input code can be calculated as follows: ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = R1 R2 V R1 R2 R1 D V V DD DD O 536 , 65 where D represents the input code in decimal (0 to 65,535). With VDD = 5 V, R1 = R2 = 10 kΩ, V 5 536 , 65 10 − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = D VO This is an output voltage range of ±5 V, with 0x0000 corre- sponding to a −5 V output, and 0xFFFF corresponding to a +5 V output. R2 = 10k Ω +5V –5V AD820/ OP295 THREE-WIRE SERIAL INTERFACE +5V AD5662 VREF VOUT VFB R1 = 10k Ω ±5V 0.1 μF 10 μF Figure 42. Bipolar Operation with the AD5662 USING THE AD5662 AS AN ISOLATED, PROGRAMMABLE, 4-20 mA PROCESS CONTROLLER In many process control system applications, 2-wire current transmitters are used to transmit analog signals through noisy environments. These current transmitters use a zero-scale signal current of 4 mA that can power the transmitter’s signal conditioning circuitry. The full-scale output signal in these transmitters is 20 mA. The converse approach to process control can also be used; a low-power, programmable current source can be used to control remotely located sensors or devices in the loop. A circuit that performs this function is shown in Figure 43. Using the AD5662 as the controller, the circuit provides a programmable output current of 4 mA to 20 mA, proportional to the DAC’s digital code. Biasing for the controller is provided by the ADR02 and requires no external trim for two reasons: (1) the ADR02’s tight initial output voltage tolerance and (2) the low supply current consumption of both the AD8627 and the AD5662. The entire circuit, including opto-couplers, consumes less than 3 mA from the total budget of 4 mA. The AD8627 regulates the output current to satisfy the current summation at the noninverting node of the AD8627. IOUT = 1/R7 (VDAC × R3/R1 + VREF × R3/R2) For the values shown in Figure 43, IOUT = 0.2435 μA × D + 4 mA where D = 0 ≤ D ≤ 65535, giving a full-scale output current of 20 mA when the AD5662’s digital code equals 0xFFFF. Offset trim at 4 mA is provided by P2, and P1 provides the circuit’s gain trim at 20 mA. These two trims do not interact because the noninverting input of the AD8627 is at virtual ground. The Schottky diode, D1, is required in this circuit to prevent loop supply power-on transients from pulling the noninverting input of the AD8627 more than 300 mV below its inverting input. Without this diode, such transients could cause phase reversal of the AD8627 and possible latch-up of the controller. The loop supply voltage compliance of the circuit is limited by the maxi- mum applied input voltage to the ADR02 and is from 12 V to 40 V. SERIAL LOAD AD5662 VLOOP 12V TO 36V 4mA TO 20mA AD8627 R1 4.7k Ω R2 18.5k Ω P1 20mA ADJUST P2 4mA ADJUST R6 3.3k Ω R3 1.5k Ω D1 Q1 2N3904 R7 100 Ω RL ADR02 Figure 43. Programmable 4–20 mA Process Controller |
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Similar Description - AD5662ARJ-1REEL7 |
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