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LTC1294 Datasheet(PDF) 18 Page - Linear Technology |
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LTC1294 Datasheet(HTML) 18 Page - Linear Technology |
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18 / 28 page  18 LTC1293/LTC1294/LTC1296 129346fs S APPLICATI I FOR ATIO LTC1294. Figure 4 shows an example of an ideal LTC1293/ 4/6 ground plane design for a two sided board. Of course this much ground plane will not always be possible, but users should strive to get as close to this ideal as possible. Bypassing For good performance, VCC must be free of noise and ripple. Any changes in the VCC voltage with respect to ground during a conversion cycle can induce errors or noise in the output code. VCC noise and ripple can be kept below 0.5mV by bypassing the VCC pin directly to the analog ground plane with a minimum of 22 µF tantalum capacitor and with leads as short as possible. The lead from the device to the VCC supply also should be kept to a minimum and the VCC supply should have a low output impedance such as obtained from a voltage regulator (e.g., LT323A). For high frequency bypassing a 0.1 µF ceramic disk placed in parallel with the 22 µF is recom- mended. Again the leads should be kept to a minimum. Figure 5 and 6 show the effects of good and poor VCC bypassing. HORIZONTAL: 10 µs/DIV HORIZONTAL: 10 µs/DIV Figure 5. Poor VCC Bypassing. Noise and Ripple Can Cause A/D Errors. Figure 6. Good VCC Bypassing Keeps Noise and Ripple on VCC Below 1mV CS VCC Analog Inputs Because of the capacitive redistribution A/D conversion techniques used, the analog inputs of the LTC1293/4/6 have capacitive switching input current spikes. These current spikes settle quickly and do not cause a problem. If large source resistances are used or if slow settling op amps drive the inputs, take care to insure the transients caused by the current spikes settle completely before the conversion begins. Figure 4. Ground Plane for the LTC1293/4/6 Figure 7. Analog Input Equivalent Circuit 6TH CLK ↑ RON = 500Ω 8TH CLK ↓ CIN = 100pF LTC1293/4/6 “+” INPUT RSOURCE + VIN + C1 “–” INPUT RSOURCE – VIN – C2 LTC1293 F07 V– 22 µF TANTALUM VCC LTC1293 F04 0.1 µF CERAMIC DISK ANALOG GROUND PLANE 0.1 µF CERAMIC 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 |
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Similar Description - LTC1294 |
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