3.3.2.2 NODE_x_PARAMS

The bit mask of the required X-line for this channel is configured here. There could be more than 1 bit set to high indicating that this node is a LUMP node.

In self-capacitance measurement, this field is configured as X_NONE (0).

In self-capacitance with driven shield measurement, this field defines the mask of Y-lines which needs to driven as a shield for this node.

The bit mask of the required Y-line for this channel is configured here. There could be more than 1 bit set to high indicating that this node is a LUMP node.

PTC measurement is divided into different phases and the number of phases varies based on the technology and device. For each increase in CSD, one clock cycle of delay is added in each phase of PTC measurement. CSD can be used to properly charge and discharge the sensor. This option may not be available for all devices.

The four LSB bits indicate the clock Prescaler and the MSB four bits indicate the Internal Y line series resistor selection.

• Prescaler : The prescaler is used to scale down the input clock to allow PTC operating frequencies. Increasing Prescaler reduces the clock frequency thus increasing the time constant. The charge time can be adjusted by the clock prescalar for devices where the CSD feature isn't available. If CSD is available, it is recommended to configure Prescaler to a minimum value (max clock frequency) and use CSD to ensure proper charging time.
• RSEL: It is applicable only for mutual capacitance and it should not be used on self-capacitance. Increasing this value reduces the amount of noise entering the PTC through the sense lines, thus improving noise performance. In mutual-capacitance this RSEL adds the resistance only on the Y line.

The four LSB bits indicate Digital Gain setting and the four MSB bits indicate the Analog Gain setting. The Gain is represented as NODE_GAIN(Analog Gain, Digital Gain).

• Digital Gain: The accumulated result from an oversampled measurement is scaled down based on digital gain. The minimum recommended ratio of oversampling/digital gain is 8. For example, if the digital gain is configured as 4, then the minimum required oversampling is 32.
• Analog Gain: PTC's integrator is adjusted to control analog gain. Increasing Analog gain reduces the amount of noise that can be integrated. Increasing Analog gain from 1 to 2 reduces integrator capacity by half, which makes the system more susceptible to noise. So it is recommended to use analog gain in noise-free systems.

  A higher gain setting increases touch delta as well as noise. So, the optimum gain setting should be used. Gain should be tuned such that the touch delta is between 40-60 counts.

Defines the number of samples taken for each measurement. A higher filter level means more samples for each measurement which averages the noise. Higher filter level settings take a longer time to do a touch measurement which affects response time. So, start with the default value and increase depending on noise levels.