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AD565ATD Datasheet(PDF) 9 Page - Analog Devices |
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AD565ATD Datasheet(HTML) 9 Page - Analog Devices |
9 / 13 page AD565A REV. –8– CONNECTING THE AD565A FOR BUFFERED VOLTAGE OUTPUT The standard current-to-voltage conversion connections using an operational amplifier are shown in Figures 1, 2, and 3 with the preferred trimming techniques. If a low offset operational amplifier (OP77, AD741L, OP07) is used, excellent performance can be obtained in many situations without trimming (an op amp with less than 0.5 mV max offset voltage should be used to keep offset errors below 1/2 LSB). If a 50 Ω fixed resistor is substituted for the 100 Ω trimmer, unipolar zero is typically within ±1/2 LSB (plus op amp offset) and full-scale accuracy is within 0.1% (0.25% max). Substituting a 50 Ω resistor for the 100 Ω bipo- lar offset trimmer gives a bipolar zero error typically within ±2 LSB (0.05%). The AD509 is recommended for buffered voltage-output applications that require a settling time to ± 1/2 LSB of 1 μs. The feedback capacitor is shown with the optimum value for each application; this capacitor is required to compen- sate for the 25 pF DAC output capacitance. FIGURE 1. UNIPOLAR CONFIGURATION This configuration provides a unipolar 0 V to 10 V output range. In this mode, the bipolar terminal, Pin 8, should be grounded if not used for trimming. 19.95k 20k 0.5mA IREF DAC IOUT = 4 IREF CODE AD565A 9.95k 5k 8k IO 20V SPAN 10V SPAN DAC OUT POWER GND –VEE REF GND BIPOLAR OFF 5k CODE INPUT LSB MSB 10V VCC REF OUT REF IN R2 100 10pF AD509 OUTPUT 0V TO +10V 100 100k +15V –15V R1 50k 2.4k Figure 1. 0 V to 10 V Unipolar Voltage Output STEP I . . . ZERO ADJUST Turn all bits OFF and adjust zero trimmer R1 until the output reads 0.000 V (1 LSB = 2.44 mV). In most cases, this trim is not needed, but Pin 8 should then be connected to Pin 12. STEP II . . . GAIN ADJUST Turn all bits ON and adjust 100 Ω gain trimmer R2 until the output is 9.9976 V. (Full scale is adjusted to 1 LSB less than nominal full scale of 10.000 V.) If a 10.2375 V full scale is desired (exactly 2.5 mV/bit), insert a 120 Ω resistor in series with the gain resistor at Pin 10 to the op amp output. FIGURE 2. BIPOLAR CONFIGURATION This configuration provides a bipolar output voltage from –5.000 V to +4.9976 V, with positive full scale occurring with all bits ON (all 1s). 19.95k 20k 0.5mA IREF DAC IOUT = 4 IREF CODE AD565A 9.95k 5k 8k IO 20V SPAN 10V SPAN DAC OUT POWER GND –VEE REF GND BIPOLAR OFF 5k CODE INPUT LSB MSB 10V VCC REF OUT REF IN R2 100 10pF AD509 OUTPUT –5V TO +5V 2.4k R1 100 Figure 2. ±5 V Bipolar Voltage Output STEP I . . . OFFSET ADJUST Turn OFF all bits. Adjust 100 Ω trimmer R1 to give –5.000 V output. STEP II . . . GAIN ADJUST Turn ON all bits. Adjust 100 Ω gain trimmer R2 to give a reading of +4.9976 V. Please note that it is not necessary to trim the op amp to obtain full accuracy at room temperature. In most bipolar situations, an op amp trim is unnecessary unless the untrimmed offset drift of the op amp is excessive. FIGURE 3. OTHER VOLTAGE RANGES The AD565A can also be easily configured for a unipolar 0 V to +5 V range or ±2.5 V and ±10 V bipolar ranges by using the additional 5 k Ω application resistor provided at the 20 V span R terminal, Pin 11. For a 5 V span (0 V to +5 V, or ±2.5 V), the two 5 k Ω resistors are used in parallel by shorting Pin 11 to Pin 9 and connecting Pin 10 to the op amp output and the bipolar offset either to ground for unipolar or to REF OUT for the bipolar offset either to ground for unipolar or to REF OUT for the bipolar range. For the ±10 V range (20 V span) use the 5 kΩ resistors in series by connecting only Pin 11 to the op amp output and the bipolar offset connected as shown. The ±10 V option is shown in Figure 3. 19.95k 20k 0.5mA IREF DAC IOUT = 4 IREF CODE AD565A 9.95k 5k 8k IO 20V SPAN 10V SPAN DAC OUT POWER GND –VEE REF GND BIPOLAR OFF 5k CODE INPUT LSB MSB 10V VCC REF OUT REF IN R2 100 10pF AD509 OUTPUT –10V TO +10V 3.0k R1 100 Figure 3. ±10 V Voltage Output F |
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