 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
AD7147 Datasheet(PDF) 26 Page - Analog Devices |
|
|
|||||||||||||||||||||||||||||
AD7147 Datasheet(HTML) 26 Page - Analog Devices |
|
|
26 / 73 page  Data Sheet AD7147 Rev. D | Page 25 of 72 THRESHOLD EQUATIONS On-Chip Logic Stage High Threshold Y SENSITIVIT THRESHOLD POS HIGH OFFSET STAGEx HIGH OFFSET STAGEx HIGH OFFSET STAGEx AMBIENT SF STAGEx THRESHOLD HIGH STAGEx _ _ 16 4 _ _ _ _ 4 _ _ _ _ _ _ × ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − + ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + = (1) On-Chip Logic Stage Low Threshold Y SENSITIVIT THRESHOLD NEG LOW OFFSET STAGEx LOW OFFSET STAGEx LOW OFFSET STAGEx AMBIENT SF STAGEx THRESHOLD LOW STAGEx _ _ 16 4 _ _ _ _ 4 _ _ _ _ _ _ × ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − + ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + = (2) CAPACITANCE SENSOR BEHAVIOR WITH CALIBRATION The AD7147 on-chip adaptive calibration algorithm prevents sensor detection errors such as the one shown in Figure 36. This is achieved by monitoring the CDC ambient levels and readjusting the initial STAGEx_OFFSET_HIGH and STAGEx_OFFSET_LOW values according to the amount of ambient drift measured on each sensor. Based on the new stage offset values, the internal STAGEx_HIGH_THRESHOLD and STAGEx_LOW_THRESHOLD values described in Equation 1 and Equation 2 are automatically updated. This closed-loop routine ensures the reliability and repeatable operation of every sensor connected to the AD7147 when they are subjected to dynamic environmental conditions. Figure 37 shows a simplified example of how the AD7147 applies the adaptive calibration process, resulting in no interrupt errors even with changing CDC ambient levels due to dynamic environmental conditions. t SENSOR 1 INT ASSERTED 1 2 3 4 5 6 STAGEx_HIGH_THRESHOLD (POSTCALIBRATED REGISTER VALUE) CHANGING ENVIRONMENTAL CONDITIONS 1INITIAL STAGEx_OFFSET_HIGH REGISTER VALUE. 2POSTCALIBRATED REGISTER STAGEx_HIGH_THRESHOLD. 3POSTCALIBRATED REGISTER STAGEx_HIGH_THRESHOLD. 4INITIAL STAGEx_LOW_THRESHOLD. 5POSTCALIBRATED REGISTER STAGEx_LOW_THRESHOLD. 6POSTCALIBRATED REGISTER STAGEx_LOW_THRESHOLD. CDC AMBIENT VALUE DRIFTING STAGEx_LOW_THRESHOLD (POSTCALIBRATED REGISTER VALUE) SENSOR 2 INT ASSERTED Figure 37. Typical Sensor Behavior with Calibration Applied on the Data Path SLOW FIFO As shown in Figure 34, there are a number of FIFOs implemented on the AD7147. These FIFOs are located in Bank 3 of the on-chip memory. The slow FIFOs are used by the on-chip logic to monitor the ambient capacitance level from each sensor. AVG_FP_SKIP and AVG_LP_SKIP In Register 0x001, Bits[13:12] are the slow FIFO skip control for full power mode, AVG_FP_SKIP. Bits[15:14] in the same register are the slow FIFO skip control for low power mode, AVG_LP_SKIP, and determine which CDC samples are not used (skipped) in the slow FIFO. Changing the values of the AVG_FP_SKIP and AVG_LP_SKIP bits slows down or speeds up the rate at which the ambient capacitance value tracks the measured capacitance value read by the converter: • Slow FIFO update rate in full power mode = AVG_FP_SKIP × [(3 × Decimation Rate) × (SEQUENCE_STAGE_NUM + 1) × (FF_SKIP_CNT + 1) × 4 × 10−7]. • Slow FIFO update rate in low power mode = (AVG_LP_SKIP + 1) × [(3 × Decimation Rate) × (SEQUENCE_STAGE_NUM + 1) × (FF_SKIP_CNT + 1) × 4 x 10−7]/[(FF_SKIP_CNT + 1) + LP_CONV_DELAY]. The slow FIFO is used by the on-chip logic to track the ambient capacitance value. The slow FIFO expects to receive samples from the converter at a rate between 33 ms and 40 ms. AVG_FP_SKIP and AVG_LP_SKIP are used to normalize the frequency of the samples going into the FIFO, regardless of how many conversion stages are in a sequence. Determining the AVG_FP_SKIP and AVG_LP_SKIP values is required only once during the initial setup of the capacitance sensor interface. The recommended values for these settings when using all 12 conversion stages on the AD7147 are as follows: • AVG_FP_SKIP = 00 = skip three samples • AVG_LP_SKIP = 00 = skip zero samples |
|
Link URL |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link to Datasheet | Link Exchange | Manufacturer List 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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
