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MCP3008T Datasheet(PDF) 23 Page - Microchip Technology |
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MCP3008T Datasheet(HTML) 23 Page - Microchip Technology |
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23 / 40 page  © 2008 Microchip Technology Inc. DS21295D-page 23 MCP3004/3008 6.4 Layout Considerations When laying out a printed circuit board for use with analog components, care should be taken to reduce noise wherever possible. A bypass capacitor should always be used with this device and should be placed as close as possible to the device pin. A bypass capacitor value of 1 µF is recommended. Digital and analog traces should be separated as much as possible on the board, with no traces running underneath the device or bypass capacitor. Extra precautions should be taken to keep traces with high- frequency signals (such as clock lines) as far as possible from analog traces. Use of an analog ground plane is recommended in order to keep the ground potential the same for all devices on the board. Providing VDD connections to devices in a “star” configuration can also reduce noise by eliminating return current paths and associated errors (see Figure 6-4). For more information on layout tips when using A/D converters, refer to AN688, “Layout Tips for 12-Bit A/D Converter Applications” . FIGURE 6-4: VDD traces arranged in a ‘Star’ configuration in order to reduce errors caused by current return paths. 6.5 Utilizing the Digital and Analog Ground Pins The MCP3004/3008 devices provide both digital and analog ground connections to provide additional means of noise reduction. As is shown in Figure 6-5, the analog and digital circuitry is separated internal to the device. This reduces noise from the digital portion of the device being coupled into the analog portion of the device. The two grounds are connected internally through the substrate which has a resistance of 5 -10Ω. If no ground plane is utilized, both grounds must be connected to VSS on the board. If a ground plane is available, both digital and analog ground pins should be connected to the analog ground plane. If both an analog and a digital ground plane are available, both the digital and the analog ground pins should be connected to the analog ground plane. Following these steps will reduce the amount of digital noise from the rest of the board being coupled into the A/D converter. FIGURE 6-5: Separation of Analog and Digital Ground Pins. VDD Connection Device 1 Device 2 Device 3 Device 4 MCP3004/08 Analog Ground Plane DGND AGND VDD 0.1 µF Substrate 5 - 10Ω Digital Side -SPI Interface -Shift Register -Control Logic Analog Side -Sample Cap -Capacitor Array -Comparator |
Similar Part No. - MCP3008T |
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Similar Description - MCP3008T |
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