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AD420ARZ-32 Fiches technique(PDF) 10 Page - Analog Devices |
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AD420ARZ-32 Fiches technique(HTML) 10 Page - Analog Devices |
10 / 16 page AD420 Rev. H | Page 10 of 16 APPLICATIONS INFORMATION CURRENT OUTPUT The AD420 can provide 4 mA–20 mA, 0 mA–20 mA, or 0 mA– 24 mA output without any active external components. Filter capacitors C1 and C2 can be any type of low cost ceramic capacitors. To meet the specified full-scale settling time of 3 ms, low dielectric absorption capacitors (NPO) are required. Suitable values are C1 = 0.01 μF and C2 = 0.01 μF. 5 2 20 14 15 11 21 23 4 6 18 7 8 9 IOUT (4mA TO 20mA) RLOAD VCC VLL AD420 GND 0.1µF 0.1µF REF IN REF OUT C1 C2 DATA IN CLOCK LATCH CLEAR RANGE SELECT 2 RANGE SELECT 1 Figure 6. Standard Configuration DRIVING INDUCTIVE LOADS When driving inductive or poorly defined loads ,connect a 0.01 μF capacitor between IOUT (Pin 18) and GND (Pin 11). This ensures stability of the AD420 with loads beyond 50 mH. There is no maximum capacitance limit. The capacitive component of the load may cause slower settling, though this may be masked by the settling time of the AD420. A programmed change in the current may cause a back EMF voltage on the output that may exceed the compliance of the AD420. To prevent this voltage from exceeding the supply rails connect protective diodes between IOUT and each of VCC and GND. VOLTAGE-MODE OUTPUT Since the AD420 is a single supply device, it is necessary to add an external buffer amplifier to the VOUT pin to obtain a selection of bipolar output voltage ranges as shown in Figure 7. 5 2 20 14 15 11 21 23 4 6 17 7 8 9 VOUT VOUT R2 R3 R1 VCC VLL AD420 GND 0.1µF 0.1µF REF IN REF OUT C1 C2 DATA IN CLOCK LATCH CLEAR RANGE SELECT 2 RANGE SELECT 1 Figure 7. Table 7. Buffer Amplifier Configuration R1 R2 R3 VOUT Open Open 0 0 V − 5 V Open R R R Open R ±5 V R 2R 2R ±10 V Suitable R = 5 kΩ. OPTIONAL SPAN AND ZERO TRIM For users who would like lower than the specified values of offset and gain error, Figure 8 shows a simple way to trim these parameters. Care should be taken to select low drift resistors because they affect the temperature drift performance of the DAC. The adjustment algorithm is iterative. The procedure for trimming the AD420 in the 4 mA–20 mA mode can be accomplished as follows: 1. Offset adjust. Load all zeros. Adjust RZERO for 4.00000 mA of output current. 2. Gain adjust. Load all ones. Adjust RSPAN for 19.99976 mA (FS − 1 LSB) of output current. Return to Step I and iterate until convergence is obtained. 5 2 20 14 15 16 11 21 23 4 6 18 19 7 8 9 IOUT (4mA TO 20mA) RLOAD 5kΩ RSPAN2 500Ω RSPAN 10kΩ RZERO BOOST VCC AD420 GND REF OUT C1 C2 DATA IN CLOCK LATCH CLEAR RANGE SELECT 2 RANGE SELECT 1 VLL 0.1µF 0.1µF Figure 8. Offset and Gain Adjust Variation of RZERO between REF OUT (5 V) and GND leads to an offset adjust range from −1.5 mA to 6 mA, (1.5 mA/V centered at 1 V). The 5 kΩ RSPAN2 resistor is connected in parallel with the internal 40 W sense resistor, which leads to a gain increase of +0.8%. As RSPAN is changed to 500 Ω, the voltage on REF IN is attenuated by the combination of RSPAN and the 30 kΩ REF IN input resistance. When added together with RSPAN2 this results in an adjustment range of −0.8% to +0.8%. |
Numéro de pièce similaire - AD420ARZ-32 |
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Description similaire - AD420ARZ-32 |
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