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LTC1287CI Datasheet(PDF) 8 Page - Linear Technology |
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LTC1287CI Datasheet(HTML) 8 Page - Linear Technology |
8 / 16 page 8 LTC1287 S APPLICATI I FOR ATIO specified at 3.3V. The output DOUT is also compatible with the above standards. The following summarizes such levels. VOH (no load) VCC – 0.1V VOL (no load) 0.1V VOH 0.9 × VCC VOL 0.1 × VCC VIH 0.7 × VCC VIL 0.2 × VCC The LTC1287 can be driven with 5V logic even when VCC is at 3.3V. This is due to a unique input protection device that is found on the LTC1287. Microprocessor Interfaces The LTC1287 can interface directly (without external hard- ware) to most popular microprocessor (MPU) synchro- nous serial formats. If an MPU without a serial interface is used, then three of the MPU’s parallel port lines can be programmed to form the serial link to the LTC1287. Many of the popular MPUs can operate with 3V supplies. For example the MC68HC11 is an MPU with a serial format (SPI). Likewise parallel MPUs that have the 8051 type architecture are also capable of operating at this voltage range. The code for these processors remains the same and can be found in the LTC1292 data sheet. Sharing the Serial Interface The LTC1287 can share the same two-wire serial interface with other peripheral components or other LTC1287s (Figure 2). In this case, the CS signals decide which LTC1287 is being addressed by the MPU. Figure 2. Several LTC1287s Sharing One 2-Wire Serial Interface Figure 3. Example Ground Plane for the LTC1287 LTC1287 2 CHANNELS 2 CHANNELS 2 CHANNELS CS CS CS 2 2 2 2 2-WIRE SERIAL INTERFACE TO OTHER PERIPHERALS OR LTC1287s 2 10 OUTPUT PORT SERIAL DATA MPU LTC1287 F02 LTC1287 LTC1287 ANALOG CONSIDERATIONS Grounding The LTC1287 should be used with an analog ground plane and single point grounding techniques. Do not use wire wrapping techniques to breadboard and evaluate the device. To achieve the optimum performance use a PC board. The ground pin (Pin 4) should be tied directly to the ground plane with minimum lead length (a low profile socket is fine). Pin 7 (VCC) should be bypassed to the ground plane with a 22 µF (minimum value) tantalum with leads as short as possible and as close as possible to the pin. A 0.1 µF ceramic disk also should be placed in parallel with the 22 µFandagainwithleadsasshortaspossibleandasclose to VCC as possible. Figure 3 shows an example of an ideal LTC1287 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 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 1 2 3 4 5 6 7 8 LTC1287 22 µF TANTALUM VCC LTC1287 F03/DB 0.1 µF |
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