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AD8293G160 Fiches technique(PDF) 11 Page - Analog Devices |
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AD8293G160 Fiches technique(HTML) 11 Page - Analog Devices |
11 / 16 page AD8293G80/AD8293G160 Rev. 0 | Page 11 of 16 APPLICATIONS INFORMATION OVERVIEW The AD8293G80/AD8293G160 reduce board area by integrating filter components, such as Resistors R1, R2, and R3, as shown in Figure 19. Two outputs are available to the user: OUT (Pin 6) and ADC OUT (Pin 4). The difference between the two is the inclusion of a series 5 kΩ resistor at ADC OUT. With the addition of an external capacitor, C3, ADC OUT forms a second filter, comprising of the 5 kΩ resistor and C3, which can be used as an ADC anti- aliasing filter. In contrast, OUT is the direct output of the instru- mentation amplifier. When using the antialiasing filter, there is slightly less switching ripple at ADC OUT than when obtaining the signal directly from OUT. +5V 0.1µF 0.1µF +5V 1 8 7 5 6 4 ADC OUT OUTPUT TO ADC WITH ANTIALIASING FILTER FILT +VS –IN +IN R1 4kΩ R2 320kΩ R3 5kΩ 100kΩ 100kΩ C3 39nF OUT C2 680pF AD8293G160 REF GND 3 2 IN-AMP Figure 19. AD8293G160 with Antialiasing Filter and Level-Shifted Output (Using the Resistor Divider at the REF Pin, the Output Is Biased at 2.5 V) REFERENCE CONNECTION Unlike traditional 3-op-amp instrumentation amplifiers, parasitic resistance in series with REF (Pin 3) does not degrade CMR performance. The AD8293G80/AD8293G160 can attain extremely high CMR performance without the use of an external buffer amplifier to drive the REF pin, which is required by industry- standard instrumentation amplifiers. Reducing the need for buffer amplifiers to drive the REF pin helps to save valuable printed circuit board (PCB) space and minimizes system costs. For optimal performance in single-supply applications, REF should be set with a low noise precision voltage reference, such as the ADR44x (see Figure 20). However, for a lower system cost, the reference voltage can be set with a simple resistor voltage divider between the supply and GND (see Figure 19). This configuration results in degraded output offset performance if the resistors deviate from their ideal values. In dual-supply applications, VREF can simply be connected to GND. The REF pin current is approximately 10 pA, and as a result, an external buffer is not required. 1µF 0.1µF 0.1µF VOLTAGE REFERENCE +5V 0.1µF 1 8 7 5 6 4 ADC OUT OUTPUT FILT +VS –IN +IN R1 4kΩ R2 R3 5kΩ OUT C2 AD8293Gxx REF GND 3 2 IN-AMP Figure 20. Operating on a Single Supply Using an External Voltage Reference (The Output Can Be Used Without an Antialiasing Filter if the Signal Bandwidth Is <10 Hz) OUTPUT FILTERING The output of the AD8293G80/AD8293G160 can be filtered to reduce switching ripple. Two filters can be used in conjunction to set the filter frequency. In the example that follows, two 700 Hz filters are used in conjunction to form a 500 Hz (recommended) bandwidth. Because the filter resistors are integrated in the AD8293G80/AD8293G160, only external capacitors are needed to set the filter frequencies. The primary filter is needed to limit the amount of switching noise at the output. Regardless of the output that is being used, OUT or ADC OUT, the primary filter comprising R2 and C2 must be implemented. The R2 value depends on the model; Table 7 shows the R2 value for each model. Table 7. Internal R2 Values Model R2 (kΩ) AD8293G80 160 AD8293G160 320 The following equation results in the C2 value needed to set a 700 Hz primary filter. For a gain of 160, substitute R2 with 320 kΩ; for a gain of 80, substitute R2 with 160 kΩ. C2 = 1/(700 × 2 × π × R2) Adding an external capacitor, C3, and measuring the output from ADC OUT further reduces the correction ripple. The internal 5 kΩ resistor, labeled R3 in Figure 18, forms a low-pass filter with C3. This low-pass filter is the secondary filter. Set to 700 Hz, the secondary filter equation for C3 is as follows: C3 = 1/(700 × 2 × π × 5 kΩ) |
Numéro de pièce similaire - AD8293G160 |
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Description similaire - AD8293G160 |
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