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AD760 Arkusz danych(PDF) 8 Page - Analog Devices |
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AD760 Arkusz danych(HTML) 8 Page - Analog Devices |
8 / 12 page –8– AD760 REV. A SPAN/ BIP OFF VOUT 23 24 25 MAIN DAC REFOUT 26 REFI N R1 50 Ω 10k Ω 10k Ω 9.95k Ω AD760 +10V REF Figure 6a. 0 V to ±10 V Bipolar Voltage Output Gain Error can be adjusted to zero using the circuit shown in Figure 6b. Note that gain adjustment changes the Bipolar Zero by one half of the variation made to the full-scale output value. Therefore, to eliminate iterating between Zero (calibration) and Gain adjustment the following procedure is recommended. STEP 1 . . . ZERO ADJUST Initiate Calibration Sequence. STEP 2 . . . GAIN ADJUST Insure the CALOK pin remains high throughout the gain ad- justment process. Turn all bits on and measure the output error relative to the full-scale output of 9.99695 V. Adjust R1 until the output is minus two times the full-scale output error. For example, if the output error is –1 mV, adjust the output 2 mV higher than the previous full-scale error. STEP 3 . . . ZERO ADJUST Initiate Calibration Sequence. The AD760 will calibrate Bipolar Zero and the resulting Gain Error will be very small. Reload the DAC with all ones to check the full-scale output error. SPAN/ BIP OFF VOUT 23 24 +10V REF 25 MAIN DAC REFOUT 26 REFI N R1 100 Ω 10k Ω 10k Ω 9.95k Ω AD760 Figure 6b. 0 V to ±10 V Bipolar Voltage Output Gain Adjustment It should be noted that using external resistors will introduce a small temperature drift component beyond that inherent in the AD760. The internal resistors are trimmed to ratio-match and temperature-track other resistors on chip, even though their absolute tolerances are ±20% and absolute temperature coeffi- cients are approximately –50 ppm/°C. In the case that external resistors are used, the temperature coefficient mismatch be- tween internal and external resistors, multiplied by the sensitiv- ity of the circuit to variations in the external resistor value, will be the resultant additional temperature drift. INTERNAL/EXTERNAL REFERENCE USE The AD760 has an internal low noise buried Zener diode refer- ence that is trimmed for absolute accuracy and temperature co- efficient. This reference is buffered and optimized for use in a high speed DAC and will give long-term stability equal or supe- rior to the best discrete Zener diode references. The perfor- mance of the AD760 is specified with the internal reference driving the DAC and with the DAC alone (for use with a preci- sion external reference). The internal reference has sufficient buffering to drive external circuitry in addition to the reference currents required for the DAC (typically 1 mA to REF IN and 1 mA to BIPOLAR OFF- SET). A minimum of 2 mA is available for driving external loads. The AD760 reference output should be buffered with an external op amp if it is required to supply more than 4 mA total current. The reference is tested and guaranteed to ±0.1% max error. It is also possible to use external references other than 10 volts with slightly degraded linearity specifications. The recom- mended range of reference voltages is +5 V to +10.24 V. For example, by using the AD586 5 V reference, outputs of 0 V to +5 V or ±5 V can be realized. Using the AD586 voltage refer- ence makes it possible to operate the AD760 with ±12 V sup- plies with 10% tolerances. Figure 7 shows the AD760 using the AD586 precision 5 V refer- ence in the bipolar configuration. The highest grade AD586MN is specified with a drift of 2 ppm/°C. This circuit includes an optional potentiometer that can be used to adjust the gain error in a manner similar to that described in the Bipolar Configura- tion section. Use +4.999847 V as the full-scale output value. The AD760 can also be used with the AD587, 10 V reference, using the same configuration shown in Figure 7 to produce a ±10 V output. The highest grade AD587L is specified at 5 ppm/°C. SPAN/BIP OFF VOUT 23 24 +10V REF 25 MAIN DAC REFOUT 26 REFI N 100 Ω 10k Ω 10k Ω 9.95k Ω AD760 AD586 2 4 6 VOUT +VCC Figure 7. Using the AD760 with the AD586 5 V Reference OUTPUT SETTLING AND GLITCH The AD760’s output buffer amplifier typically settles to within 0.0008% FS (1/2 LSB) of its final value in 8 µs for a full-scale step. Figures 8a and 8b show settling for a full scale and an LSB step, respectively, with a 2 k , 1000 pF load applied. The guaranteed maximum settling time at +25°C for a full-scale step is 13 µs with this load. The typical settling time for a 1 LSB step is 2.5 µs. |
Podobny numer części - AD760 |
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Podobny opis - AD760 |
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