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MCP3021 Datasheet(PDF) 19 Page - Microchip Technology |
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MCP3021 Datasheet(HTML) 19 Page - Microchip Technology |
19 / 26 page 2003 Microchip Technology Inc. DS21805A-page 19 MCP3021 6.3 Device Polling In some instances, it may be necessary to test for MCP3021 presence on the I2C bus without performing a conversion, described in Figure 6-4. Here we are set- ting the R/W bit in the address byte to a zero. The MCP3021 will then acknowledge by pulling SDA low during the ACK clock and then release the bus back to the I2C master. A stop or repeated start bit can then be issued from the master and I2C communication can continue. FIGURE 6-4: Device Polling. 6.4 Device Power and Layout Considerations 6.4.1 POWERING THE MCP3021 VDD supplies the power to the device as well as the ref- erence voltage. A bypass capacitor value of 0.1 µF is recommended. Adding a 10 µF capacitor in parallel is recommended to attenuate higher frequency noise present in some systems. FIGURE 6-5: Powering the MCP3021. 6.4.2 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 from VDD to ground should always be used with this device and should be placed as close as possible to the device pin. A bypass capacitor value of 0.1 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 the 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. The MCP3021 should be connected entirely to the ana- log ground place, as well as the analog power trace. The pull-up resistors can be placed close to the microcontroller and tied to the digital power or VCC. 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 current return paths and associated errors (Figure 6-6). For more information on layout tips when using the MCP3021 or other ADC devices, refer to AN688, “Layout Tips for 12-Bit A/D Converter Applications”. FIGURE 6-6: VDD traces arranged in a ‘Star’ configuration in order to reduce errors caused by current return paths. 6.4.3 USING A REFERENCE FOR SUPPLY The MCP3021 uses VDD as power and also as a refer- ence. In some applications, it may be necessary to use a stable reference to achieve the required accuracy. Figure 6-7 shows an example using the MCP1541 as a 4.096V 2% reference. FIGURE 6-7: Stable Power and Reference Configuration. 123 456 78 9 SCL SDA 1 00 1 A2A1A0 0 Start Bit Address Byte Address bits Device bits R/W Start Bit MCP3021 response VDD VDD AIN SCL SDA To Microcontroller 10 µF MCP3021 0.1 µF VCC RPU RPU VDD Connection Device 1 Device 2 Device 3 Device 4 VDD VDD 4.096V Reference 1µF 0.1 µF MCP1541 CL AIN MCP3021 VCC RPU SCL SDA |
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Similar Description - MCP3021 |
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