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AD1862 bảng dữ liệu(PDF) 6 Page - Analog Devices |
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AD1862 bảng dữ liệu(HTML) 6 Page - Analog Devices |
6 / 12 page AD1862 –6– REV. A Analog Circuit Considerations GROUNDING RECOMMENDATIONS The AD1862 has two ground pins, designated analog ground (AGND) and digital ground (DGND). The analog ground pin is the “high-quality” ground reference for the device. The ana- log ground pin should be connected to the analog common point in the system. The reference bypass capacitor, the nonin- verting terminal of the current-to-voltage conversion op amp, and any output loads should be connected to this point. The digital ground pin returns ground current from the digital logic portions of the AD1862 circuitry. This pin should be connected to the digital common point in the system. As illustrated in Figure 7, AGND and DGND should be con- nected together at one point in the system. AD1862 TOP VIEW (Not to Scale) 1 2 3 4 5 6 7 89 10 11 12 13 14 15 16 DGND AGND Figure 7. Grounding and Bypassing Recommendations POWER SUPPLIES AND DECOUPLING The AD1862 has four power supply input pins. ±V S provide the supply voltages which operate the linear portions of the DAC in- cluding the voltage reference and control amplifier. The ±V S supplies are designed to operate with ±12 volts. The ±V L supplies operate the digital portions of the chip includ- ing the input shift register, the input latching circuitry and the TTL-to-CMOS level shifters. The ±V L supplies are designed to be operated from ±5 V to ±12 V supplies subject only to the limitation that –VL may not be more negative than –VS. Decoupling capacitors should be used on all power supply input pins. Good engineering practice suggests that these capacitors be placed as close as possible to the package pins and the com- mon points. The logic supplies, ±V L, should be decoupled to DGND and the analog supplies, ±V S, should be decoupled to AGND. EXTERNAL NOISE REDUCTION COMPONENTS Two external capacitors are required to achieve low-noise opera- tion. Their correct connection is illustrated in Figure 8. Capacitor C1 is connected between the pin labeled NR1 and analog com- mon. C1 forms a low-pass filter element which reduces noise con- tributed by the voltage reference circuitry. The proper choice for this capacitor is a tantalum type with value of 10 µF or more. This capacitor should be connected to the package pins as closely as possible. This will minimize the effects of parasitic inductance of the leads and connections circuit connections. –12V ANALOG SUPPLY C2 C1 AD1862 TOP VIEW (Not to Scale) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 + + NOTE: PIN 1 IS "HIGH QUALITY" RETURN FOR BIAS CAP. Figure 8. Noise Reduction Capacitors Capacitor C2 is connected between the pin labeled NR2 and the negative analog supply, –VS. This capacitor reduces the portion of output noise contributed by the control amplifier circuitry. C2 should be chosen to be a tantalum capacitor with a value of about 1 µF. Again, the connections between the AD1862 and C2 should be made as short as possible. The recommended values for C1 and C2 are 10 µF and 1 µF, respectively. The ratio between C1 and C2 should be approxi- mately 10. Additional noise reduction can be gained by choos- ing slightly higher values for C1 and C2 such as 22 µF and 2.2 µF. Figure 2 illustrates the noise performance of the AD1862 with 10 µF and 1 µF. EXTERNAL AMPLIFIER CONNECTIONS The AD1862 is a current-output D/A converter. Therefore, an external amplifier, in combination with the on-board feedback resistor, is required to derive an output voltage. Figure 9 illus- trates the proper connections for an external operational ampli- fier. The output of the AD1862 is intended to drive the summing junction of an external current-to-voltage conversion op amp. Therefore, the voltage on the output current pin of the AD1862 should be approximately the same as that on the AGND pin of the device. The on-board 3 k Ω feedback resistor and the ±1 mA output current typically have ±1% tolerance or less. This makes the choice of external components very simple and eliminates addi- tional trimming. For example, if a user wishes to derive an out- put voltage higher than the ±3 V swing offered by the output current and feedback resistor combination, all that is required is to combine a standard value resistor with the feedback resistor to achieve the appropriate output voltage swing. This technique can be extended to include the choice of elements in the deemphasis network, etc. |
Số phần tương tự - AD1862 |
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Mô tả tương tự - AD1862 |
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