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AD711 Datasheet(PDF) 10 Page - Analog Devices |
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AD711 Datasheet(HTML) 10 Page - Analog Devices |
10 / 16 page REV. E AD711 –10– AD711K CF VOUT 0.1 F 0.1 F –15 +15 C1 33pF R2* OUT1 RFB VDD VREF DGND AGND R1* VIN ANALOG COMMON GAIN ADJUST DB11-DB0 VDD AD7545 *FOR VALUES R1 AND R2, REFER TO TABLE 1 Figure 8. Unipolar Binary Operation R1 and R2 calibrate the zero offset and gain error of the DAC. Specific values for these resistors depend upon the grade of AD7545 and are shown below. Table I. Recommended Trim Resistor Values vs. Grades of the AD7545 for VDD = 5 V TRIM RESISTOR JN/AQ/SD KN/BQ/TD LN/CQ/UD GLN/GCQ/GUD R1 500 W 200 W 100 W 20 W R2 150 W 68 W 33 W 6.8 W NOISE CHARACTERISTICS The random nature of noise, particularly in the 1/f region, makes it difficult to specify in practical terms. At the same time, designers of precision instrumentation require certain guaranteed maximum noise levels to realize the full accuracy of their equipment. The AD711C grade is specified at a maximum level of 4.0 mV p-p, in a 0.1 Hz to 10 Hz bandwidth. Each AD711C receives a 100% noise test for two 10-second intervals; devices with any excursion in excess of 4.0 mV are rejected. The screened lot is then submitted to Quality Control for verification on an AQL basis. All other grades of the AD711 are sample-tested on an AQL basis to a limit of 6 mV p-p, 0.1 to 10 Hz. DRIVING THE ANALOG INPUT OF AN A/D CONVERTER An op amp driving the analog input of an A/D converter, such as that shown in Figure 11, must be capable of maintaining a constant output voltage under dynamically changing load conditions. In successive-approximation converters, the input current is compared to a series of switched trial currents. The comparison point is diode clamped but may deviate several hundred millivolts resulting in high frequency modulation of A/D input current. Figures 10a and 10b show the settling time characteristics of the AD711 when used as a DAC output buffer for the AD7545. a. Full-Scale Positive b. Full-Scale Negative Transition Transition Figure 10. Settling Characteristics for AD711 with AD7545 compared to a series of switched trial currents. The comparison point is diode clamped but may deviate several hundred milli- volts resulting in high frequency modulation of A/D input current. The output impedance of a feedback amplifier is made artificially low by the loop gain. At high frequencies, where the loop gain is low, the amplifier output impedance can approach its open loop value. Most IC amplifiers exhibit a minimum open loop output impedance of 25 W due to current limiting resistors. A few hundred microamps reflected from the change in con- verter loading can introduce errors in instantaneous input Figures 8 and 9 show the AD711 and AD7545 (12-bit CMOS DAC) configured for unipolar binary (2-quadrant multiplication) or bipolar (4-quadrant multiplication) operation. Capacitor C1 provides phase compensation to reduce overshoot and ringing. +15V 0.1 F 0.1 F AD711K –15V R3 10k 1% +15V 0.1 F 0.1 F AD711K –15V R5 20k 1% R4 20k 1% R2* C1 33pF OUT1 RFB VDD VREF DGND AGND R1* VIN GAIN ADJUST DB11-DB0 VDD VOUT AD7545 12 DATA INPUT ANALOG COMMON *FOR VALUES R1 AND R2, REFER TO TABLE 1 Figure 9. Bipolar Operation +15V 0.1 F 0.1 F AD711 –15V R2 100 GAIN ADJUST 12/8 R1 100 OFFSET ADJUST CS AO R/C CE REF IN REF OUT BIP OFF 10VIN 20VIN ANA COM STS HIGH BITS MIDDLE BITS LOW BITS +5V +15V –15V DIG COM AD574 10V ANALOG INPUT ANALOG COM Figure 11. AD711 as ADC Unity Gain Buffer |
Número de pieza similar - AD711_02 |
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Descripción similar - AD711_02 |
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