AD7142 Analog Devices, AD7142 Datasheet - Page 25

• Manufacturer Part Number: AD7142
• Description: Programmable Controller for Capacitance Touch Sensors
• Manufacturer: Analog Devices

Specifications of AD7142

• Resolution (bits): 16bit
• # Chan: 14
• Sample Rate: 250kSPS
• Interface: I²C/Ser 2-Wire,Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: ± 2 pF (Delta C)
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

Table 13. Additional Information about Environmental Calibration and Adaptive Threshold Registers
Register
NEG_THRESHOLD_SENSITIVITY
NEG_PEAK_DETECT
POS_THRESHOLD_SENSITIVITY
POS_PEAK_DETECT
STAGE_OFFSET_LOW
STAGE_OFFSET_HIGH
STAGE_OFFSET_HIGH_CLAMP
STAGE_OFFSET_LOW_CLAMP
STAGE_SF_AMBIENT
STAGE_HIGH_THRESHOLD
STAGE_LOW_THRESHOLD
Register
Location
Bank 2
Bank 2
Bank 2
Bank 2
Bank 2
Bank 2
Bank 2
Bank 2
Bank 3
Bank 3
Bank 3
Figure 37. Tracking the Minimum and Maximum Average Sensor Values
16-BIT
CDC
Σ-Δ
16
Description
Used in Equation 2. This value is programmed once at start up.
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 min average CDC value. If the output of the CDC gets within the
NEG_PEAK_DETECT percentage of the min average, only then is the min average value
updated.
Used in Equation 1. This value is programmed once at start up.
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 max average CDC value. If the output of the CDC gets within the
POS_PEAK_DETECT percentage of the min average, only then is the max average value
updated.
Used in Equation 2. An initial value (based on sensor characterization) is programmed
into this register at start up. The AD7142 on chip calibration algorithm automatically
updates this register based on the amount of sensor drift due to changing ambient
conditions. Set to 80% of the STAGE_OFFSET_LOW_CLAMP value.
Used in Equation 1. An initial value (based on sensor characterization) is programmed
into this register at start up. The AD7142 on chip calibration algorithm automatically
updates this register based on the amount of sensor drift due to changing ambient
conditions. Set to 80% of the STAGE_OFFSET_HIGH_CLAMP value.
Used by internal environmental calibration and adaptive threshold algorithms only.
An initial value (based on sensor characterization) is programmed into this register at
start up. The value in this register prevents a user from causing a sensor’s output value
to exceed the expected nominal value.
Set to the maximum expected sensor response, maximum change in CDC output code .
Used by internal environmental calibration and adaptive threshold algorithms only.
An initial value (based on sensor characterization) is programmed into this register at
start up. The value in this register prevents a user from causing a sensor’s output value
to exceed the expected nominal value.
Set to the minimum expected sensor response, minimum change in CDC output code .
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.
Equation 1 value.
Equation 2 value.
DETECTION
DETECTION
MAX LEVEL
MIN LEVEL
LOGIC
LOGIC
Rev. A | Page 25 of 72
STAGE_HIGH_THRESHOLD
STAGE_LOW_THRESHOLD
STAGE_MAX_WORD0
STAGE_MAX_WORD1
STAGE_MAX_WORD2
STAGE_MAX_WORD3
STAGE_MIN_WORD0
STAGE_MIN_WORD1
STAGE_MIN_WORD2
STAGE_MIN_WORD3
BANK 3 REGISTERS
BANK 3 REGISTERS
BANK 3 REGISTERS
BANK 3 REGISTERS
BANK 3 REGISTERS
BANK 3 REGISTER3
STAGE_MAX_TEMP
STAGE_MIN_TEMP
STAGE_MAX_AVG
STAGE_MIN_AVG
BANK 3
REGISTERS
BANK 3
REGISTERS
AD7142