AD7147 Datasheet, PDF (26/68 Pages) Analog Devices – CapTouch™ Programmable Controller for Single-Electrode Capacitance Sensors

AD7147
Σ-Δ
16
16-BIT
CDC
MAXIMUM
LEVEL
DETECTION
LOGIC
STAGEx_MAX_WORD0
STAGEx_MAX_WORD1
STAGEx_MAX_WORD2
STAGEx_MAX_WORD3
BANK 3 REGISTERS
STAGEx_MAX_AVG
BANK 3 REGISTERS
STAGEx_MAX_TEMP
BANK 3 REGISTERS
STAGEx_HIGH_THRESHOLD
BANK 3 REGISTERS
STAGEx_MIN_WORD0
STAGEx_MIN_WORD1
STAGEx_MIN_WORD2
STAGEx_MIN_WORD3
BANK 3 REGISTERS
MINIMUM
LEVEL
DETECTION
LOGIC
STAGEx_MIN_AVG
BANK 3 REGISTERS
STAGEx_MIN_TEMP
BANK 3 REGISTERS
STAGEx_LOW_THRESHOLD
BANK 3 REGISTERS
Figure 38. Tracking the Minimum and Maximum Average Sensor Values
Table 14. Additional Information About Environmental Calibration and Adaptive Threshold Registers
Register/Bit
Register
Location Description
NEG_THRESHOLD_SENSITIVITY
Bank 2 Used in Equation 2. This value is programmed once at startup.
NEG_PEAK_DETECT
Bank 2 Used by internal adaptive threshold logic only.
The NEG_PEAK_DETECT is set to a percentage of the difference between the ambient
CDC value and the minimum average CDC value. If the output of the CDC approaches the
NEG_PEAK_DETECT percentage of the minimum average, the minimum average value is updated.
POS_THRESHOLD_SENSITIVITY
Bank 2 Used in Equation 1. This value is programmed once at startup.
POS_PEAK_DETECT
Bank 2 Used by internal adaptive threshold logic only.
The POS_PEAK_DETECT is set to a percentage of the difference between the ambient
CDC value and the maximum average CDC value. If the output of the CDC approaches the
POS_PEAK_DETECT percentage of the maximum average, the maximum average value is updated.
STAGEx_OFFSET_LOW
Bank 2
Used in Equation 2. An initial value (based on sensor characterization) is programmed into
this register at startup. The AD7147 on-chip calibration algorithm automatically updates this
register based on the amount of sensor drift due to changing ambient conditions. Set this
register to 80% of the STAGEx_OFFSET_LOW_CLAMP value.
STAGEx_OFFSET_HIGH
Bank 2
Used in Equation 1. An initial value (based on sensor characterization) is programmed into
this register at startup. The AD7147 on-chip calibration algorithm automatically updates this
register based on the amount of sensor drift due to changing ambient conditions. Set this
register to 80% of the STAGEx_OFFSET_HIGH_CLAMP value.
STAGEx_OFFSET_HIGH_CLAMP
Bank 2
Used by internal environmental calibration and adaptive threshold algorithms only.
An initial value (based on sensor characterization) is programmed into this register at startup.
The value in this register prevents a user from causing a sensor’s output value to exceed the
expected nominal value.
Set this register to the maximum expected sensor response or the maximum change in CDC
output code.
STAGEx_OFFSET_LOW_CLAMP
Bank 2
Used by internal environmental calibration and adaptive threshold algorithms only.
An initial value (based on sensor characterization) is programmed into this register at startup.
The value in this register prevents a user from causing a sensor’s output value to exceed the
expected nominal value.
Set this register to the minimum expected sensor response or the minimum change in CDC
output code.
STAGEx_SF_AMBIENT
Bank 3
Used in Equation 1 and Equation 2. This is the ambient sensor output when the sensor is not
touched, as calculated using the slow FIFO.
STAGEx_HIGH_THRESHOLD
Bank 3 Equation 1 value.
STAGEx_LOW_THRESHOLD
Bank 3 Equation 2 value.
Rev. 0 | Page 26 of 68