Moteur de recherche de fiches techniques de composants électroniques |
|
AD7156 Fiches technique(PDF) 25 Page - Analog Devices |
|
AD7156 Fiches technique(HTML) 25 Page - Analog Devices |
25 / 29 page AD7156 Rev. 0 | Page 24 of 28 HARDWARE DESIGN CONSIDERATIONS OVERVIEW The AD7156 is an interface to capacitive sensors. On the input side, Sensor CX can be connected directly between the AD7156 EXC and CIN pins. The way it is connected and the electrical parameters of the sensor connection, such as parasitic resistance or capacitance, can affect the system performance. Therefore, any circuit with additional components in the capacitive front end, such as overvoltage protection, has to be carefully designed, considering the AD7156 specified limits and informa- tion provided in this section. On the output side, the AD7156 can work as a standalone device, using the power-up default register settings and flagging the result on the digital outputs. Alternatively, the AD7156 can be interfaced to a microcontroller via the 2-wire serial interface, offering flexibility by overwriting the AD7156 register values from the host with a user-specific setup. PARASITIC CAPACITANCE TO GROUND DATA CDC EXC CGND1 CIN CGND2 CX Figure 42. Parasitic Capacitance to Ground The CDC architecture used in the AD7156 measures the capacitance, CX, connected between the EXC pins and the CIN pins. In theory, any capacitance, CGND, to ground should not affect the CDC result (see Figure 42). The practical implementation of the circuitry in the chip implies certain limits, and the result is gradually affected by capacitance to ground (for information about the allowed capacitance to GND for CIN and information about excitation see Table 1 and Figure 4 to Figure 9). PARASITIC RESISTANCE TO GROUND DATA CDC EXC RGND1 CIN RGND2 CX Figure 43. Parasitic Resistance to Ground The AD7156 CDC result is affected by a leakage current from CX to ground; therefore, CX should be isolated from the ground. The equivalent resistance between CX and ground should be maximized (see Figure 43). For more information, see Figure 10 to Figure 13. PARASITIC PARALLEL RESISTANCE DATA CDC EXC CIN RP CX Figure 44. Parasitic Parallel Resistance The AD7156 CDC measures the charge transfer between the EXC and CIN pins. Any resistance connected in parallel to the measured capacitance, CX (see Figure 44), such as the parasitic resistance of the sensor, also transfers charge. Therefore, the parallel resistor is seen as an additional capacitance in the output data. The equivalent parallel capacitance (or error caused by the parallel resistance) can be approximately calculated as 4 1 × × = EXC P P f R C where: RP is the parallel resistance. fEXC is the excitation frequency. For additional information, see Figure 15. |
Numéro de pièce similaire - AD7156_17 |
|
Description similaire - AD7156_17 |
|
|
Lien URL |
Politique de confidentialité |
ALLDATASHEET.FR |
ALLDATASHEET vous a-t-il été utile ? [ DONATE ] |
À propos de Alldatasheet | Publicité | Contactez-nous | Politique de confidentialité | Echange de liens | Fabricants All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |