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AD5044 Datasheet(PDF) 24 Page - Analog Devices |
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AD5044 Datasheet(HTML) 24 Page - Analog Devices |
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24 / 28 page  AD5024/AD5044/AD5064 Rev. 0 | Page 24 of 28 APPLICATIONS USING A REFERENCE AS A POWER SUPPLY Because the supply current required by the AD5024/AD5044/ AD5064 is extremely low, an alternative option is to use a voltage reference to supply the required voltage to the parts (see Figure 52). This is especially useful if the power supply is quite noisy or if the system supply voltages are at some value other than 5 V (for example, 15 V). The voltage reference outputs a steady supply voltage for the AD5024/AD5044/AD5064. If the low dropout REF195 is used, it must supply 3 mA of current to the AD5024/ AD5044/AD5064, with no load on the output of the DAC. When the DAC output is loaded, the REF195 also needs to supply the current to the load. The total current required (with a 5 kΩ load on the DAC output) is 3 mA + (5 V/5 kΩ) = 4 mA The load regulation of the REF195 is typically 2 ppm/mA, which results in a 3 ppm (15 μV) error for the 4 mA current drawn from it. This corresponds to a 0.196 LSB error. SYNC SCLK DIN 15V 5V VOUT = 0V TO 5V VDD REF195 AD5024/ AD5044/ AD5064 3-WIRE SERIAL INTERFACE Figure 52. REF195 as Power Supply to the AD5024/AD5044/AD5064 BIPOLAR OPERATION The AD5024/AD5044/AD5064 have been designed for single- supply operation, but a bipolar output range is also possible using the circuit shown in Figure 53. 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. Assuming VDD = VREF, the output voltage for any input code can be calculated as follows: ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × − ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = R1 R2 V R1 R2 R1 D V V DD DD OUT 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 V OUT 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. 3-WIRE SERIAL INTERFACE R2 = 10kΩ +5V AD820/ OP295 +5V AD5024/ AD5044/ AD5064 VDD VOUT R1 = 10kΩ ±5V 0.1µF 10µF –5V Figure 53. Bipolar Operation USING THE AD5024/AD5044/AD5064 WITH A GALVANICALLY ISOLATED INTERFACE In process control applications in industrial environments, it is often necessary to use a galvanically isolated interface to protect and isolate the controlling circuitry from any hazardous common-mode voltages that can occur in the area where the DAC is functioning. iCoupler® provides isolation in excess of 2.5 kV. The AD5024/AD5044/AD5064 use a 3-wire serial logic interface, so the ADuM1300 three-channel digital isolator provides the required isolation (see Figure 54). The power supply to the part also needs to be isolated, which is done by using a transformer. On the DAC side of the transformer, a 5 V regulator provides the 5 V supply required for the AD5024/ AD5044/AD5064. 0.1µF GND DIN SYNC SCLK POWER 10µF SDI SCLK DATA AD5024/ AD5044/ AD5064 VOUT VOB VOA VOC VDD VIC VIB VIA ADuM1300 5V REGULATOR Figure 54. AD5024/AD5044/AD5064 with a Galvanically Isolated Interface |
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