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CLC532 Datasheet(PDF) 10 Page - National Semiconductor (TI) |
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CLC532 Datasheet(HTML) 10 Page - National Semiconductor (TI) |
10 / 15 page Application Information (Continued) Figure 4 below describes the basic relationship between settling time (T S) and RS for various values of load capaci- tance, C L, where CCOMP = 10pF Figure 5 shows the resulting changes in bandwidth and slew rate for increasing values of C COMP. The RMS noise at the CLC532 output can be approximated as: where.... n V = input spot noise voltage; BW −3dB = Bandwidth is from Figure 5. Power Supplies and Grounding Proper power supply bypassing and grounding is essential to the CLC532’s operation. 0.1µF to .1µF ceramic chip ca- pacitor should be located very close to the individual power supply pins. Larger +6.8µF tantalum capacitors should be used within a few inches of the CLC532. The ground con- nections for these larger by-pass capacitors should be sym- metrically located relative the CLC532 output load ground connection. Harmonic distortion can be heavily influenced by non-symmetric decoupling capacitor grounding. The smaller chip capacitors located directly at the power supply pins are not particularly susceptible to this effect. Separation of analog and digital ground planes is not recom- mended. In most cases, a single low impedance ground plane will provide the best performance. In those special cases requiring separate ground planes, the following table indicates the signal and supply ground connections. Pin Functions Ground Return 1,3 Shield/Supply Returns Supplies and Inputs 5D REF Ground D REF Currents only Input Shielding The CLC532 has been designated for use in high speed wide dynamic range systems. Guarding traces and the use of the ground pins separating the analog inputs are recom- mended to maintain high isolation ( Figure 6). Likely sources of noise and interference that may couple onto the inputs, are the logic signals and power supplies to the CLC532. Other types if clock and signal traces should not be over- looked, however. The general rule in maintaining isolation has two facets, minimize the primary return ground current path impedances back to the respective signal sources, while maximizing the impedance associated with common or secondary ground current return paths. Success or failure to optimize input signal isolation can be measured directly as the isolation between the input channels with the CLC532 removed from circuit. The channel-to -channel isolation of the CLC532 can never be better than the isolation level present at its inputs. Special attention must be paid to input termination resistors. Minimizing the return current path that is common to both of the input termination resistors is essential. In the event that a ground return current from one input termination resistor is able to find a secondary path back to its signal source (which also happens to be common with either the primary or sec- ondary return path for the second input termination resistor), a small voltage can appear across the second input termi- nation resistor. The small voltage seen across the second input termination resistor will be highly correlated with the signal generating the initial return currents. This situation will severely degrade channel-to-channel isolation at the input of the CLC532, even if the CLC532 were removed from circuit. Poor isolation at the input will be transmitted directly to the output. Use of “small” value input termination resistors will also improve channel-to-channel isolation. However, extremely low values (<25 Ω) tend to stress the driving source’s ability to provide a high-quality input signal to the CLC532. Higher values tend to aggravate any layout dependent crosstalk. 75 Ω to 50Ω is a reasonable target, but the lower the better. DS012716-39 FIGURE 4. Settling Time and R S vs. CL DS012716-41 FIGURE 5. C COMP for Maximally Flat Frequency Response Channel A Connector Channel B Connector Chip Resistors Pin 1 DS012716-42 FIGURE 6. Alternate Layout Using Guard Ring www.national.com 10 |
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Similar Description - CLC532 |
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