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AD7147A Scheda tecnica(PDF) 18 Page - Analog Devices |
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AD7147A Scheda tecnica(HTML) 18 Page - Analog Devices |
18 / 69 page AD7147A Rev. B | Page 17 of 68 CAPACITANCE SENSOR INPUT CONFIGURATION Each input connection from the external capacitance sensors to the converter of the AD7147A can be uniquely configured by using the stage configuration registers in Bank 2 (see Table 39). These registers are used to configure the input pin connection setups, sensor offsets, sensor sensitivities, and sensor limits for each stage. Each sensor can be individually optimized. For example, a button sensor connected to STAGE0 can have differ- ent sensitivity and offset values than a button with another function that is connected to a different stage. CINx INPUT MULTIPLEXER SETUP Table 35 and Table 36 list the available options for the CINx_ CONNECTION_SETUP bits when the sensor input pins are connected to the CDC. The AD7147A has an on-chip multiplexer that routes the input signals from each CINx pin to the input of the converter. Each input pin can be tied to either the negative or positive input of the CDC, or it can be left floating. Each input can also be internally connected to the BIAS signal to help prevent cross- coupling. If an input is not used, always connect it to BIAS. Connecting a CINx input pin to the positive CDC input results in an increase in CDC output code when the corresponding sensor is activated. Connecting a CINx input pin to the negative CDC input results in a decrease in CDC output code when the corresponding sensor is activated. The AD7147A performs a sequence of 12 conversions. The multi- plexer can have different settings for each of the 12 conversions. For example, CIN0 is connected to the negative CDC input for conversion STAGE1, left floating for conversion STAGE1, and so on, for all 12 conversion stages. For each CINx input for each conversion stage, two bits control how the input is connected to the converter, as shown in Figure 28. Examples To connect CIN3 to the positive CDC input on Stage 0, use the following setting: STAGE0_CONNECTION[6:0] = 0xFFBF STAGE0_CONNECTION[12:7] = 0x2FFF To connect CIN0 to the positive CDC input and CIN12 to the negative CIN input on STAGE5, use the following settings: STAGE5_CONNECTION[6:0] = 0xFFFE STAGE5_CONNECTION[12:7] = 0x37FF SINGLE-ENDED CONNECTIONS TO THE CDC A single-ended connection to the CDC is defined as one CINx input connected to either the positive or negative CDC input for one conversion stage. A differential connection to the CDC is defined as one CINx input connected to the positive CDC input and a second CINx input connected to the negative input of the CDC for one conversion stage. For any stage, if a single-ended connection to the CDC is made in that stage, the SE_CONNECTION_SETUP Bits[13:12] in the STAGEx_CONNECTION[12:7] register should be applied as described in Table 12. Table 12. SE_CONNECTION_SETUP Bits SE_CONNECTION_SETUP Description 00 Do not use. 01 Single-ended connection. For this stage, there is one CINx connected to the positive CDC input. 10 Single-ended connection. For this stage, there is one CINx connected to the negative CDC input. 11 Differential connection. For this stage, there is one CINx connected to the negative CDC input and one CINx connected to the positive CDC input. The SE_CONNECTION_SETUP Bits[13:12] ensure that during a single-ended connection to the CDC, the input paths to both CDC terminals are matched, which, in turn, improves the power-supply rejection of the converter measurement. These bits should be applied in addition to setting the other bits in the STAGEx_CONNECTION registers, as outlined in the CINX Input Multiplexer Setup section. If more than one CINx input is connected to either the positive or negative input of the converter for the same conversion, set SE_CONNECTION_SETUP to 11. For example, if CIN0 and CIN3 are connected to the positive input of the CDC, set SE_CONNECTION_SETUP to 11. CIN CONNECTION SETUP BITS CIN SETTING 00 CINx FLOATING 01 CINx CONNECTED TO NEGATIVE CDC INPUT 10 CINx CONNECTED TO POSITIVE CDC INPUT 11 CINx CONNECTED TO BIAS CIN0 CIN1 CIN2 CIN3 CIN4 CIN5 CIN6 CIN7 CIN8 CIN9 CIN10 CIN11 CIN12 + – CDC Figure 28. Input Mux Configuration Options |
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