Product Info

LM746 Bluetooth® Dual Mode Audio Module
Standalone (With Embedded Bluetooth® 5 Compliant Stack)
The internal capacitance is trimmed, putting it in the mid range of the ADC. This enables measurements from 0pF to 50pF, where a capacitive touch is
between ±50fF and ±1pF.
Digital signal conditioning:
Only the enabled inputs are scanned
Enabling fewer inputs increases readings per second
Averaging of ADC readings reduces noise, this is software programmable from 1 to 64 readings in intervals to the power of 2
The internal capacitance updates using a rolling average of the ADC readings, software programmable from 1 to 215 readings in intervals to the power
of 2. For example, 32768 readings take approximately:
5.6s if polling one pad (no averaging)
33.8s if polling 6 pads (no averaging)
Pulse skipping mode is possible, reducing the current consumption. Here the system waits a programmable number of 64kHz clock cycles (maximum
29) before the next read, i.e. an 8ms maximum pause.
ADC trigger level is software programmable. If the threshold is crossed the firmware gets an interrupt.
6 hardware event registers store the pad number and trigger time, which enables the system to sense swipes.
Programmable hysteresis, with one value for all pads
Software signal conditioning (firmware):
The firmware reads ADC and Cint values after an interrupt as the hardware only stores the pad number and trigger time
Digital state machine scans pads and calibrates the internal capacitance
If a swipe happens in deep sleep the firmware reads the trigger order and event time when it wakes
up. It then reads the last ADC reading for each input, not the reading that triggered the interrupt.
VM:
Configures the hardware and gets an interrupt when a programmable threshold is crossed
Selects the range capacitance
Decides whether an event is a valid touch
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