QST104 Datasheet, PDF (12/45 Pages) STMicroelectronics – Capacitive touch sensor device 4 keys with individual key state outputs or I2C interface

Device operating modes
QST104
Caution:
● Deep Sleep mode
In Deep Sleep mode, the device enters a very low power mode indefinitely. The device
resumes its operations after receiving an I²C frame with any address or a reset.
If an I²C frame is received while in Sleep or Deep Sleep mode, the device wakes up but
does not acknowledge the frame (even if it has an I²C frame with the device address). The
host must therefore send again the frame until it is taken in account and acknowledged.
4.4
Mode selection
The device options are configured by connecting pull-up or pull-down resistors on OPTn
pins. The device operating mode is selected using option pin 1 (OPT1) while the device
settings are configured using option pins OPT2 to OPT6 (Table 3). Option pins are sampled
at power-up and after a reset.
To fit most applications, the QST104 device offers two different operating modes:
● Stand-alone mode
This mode allows the user to simply replace existing mechanical switches with a
capacitive sensing solution. It is designed for maximum flexibility and can
accommodate most popular sensing requirements via option resistors (AKS, Low
power, Max On-Duration and output modes).
In this mode, the 4 output pins reflect the status of the 4 sensing channels.
● I²C mode
In this mode, which is the most open one, the device is driven using the I²C interface.
To avoid polling, the QST device features an output interrupt pin (IRQ). The IRQ line
reports all key changes to the Master device. The QST (Slave) device can drive up to
13 general-purpose outputs.
Table 3. Operating modes
OPT1: Mode selection
Pin OPT1 is high at start-up Stand-alone mode
Pin OPT1 is low at start-up I²C mode
Option resistor function
OPT2
AKS
ADD0
OPT3 OPT4 OPT5 OPT6
LP MOD_0 MOD_1 OM
ADD1 ADD2 Unused Unused
4.5
4.5.1
Stand-alone mode
This mode allows the user to simply replace existing mechanical switch interface with a
capacitive sensing solution. It is designed for maximum flexibility and can accommodate
most popular sensing requirements via option resistors (see Figure 3).
Main features
● Pins KOUT1 to KOUT4 directly reflect the state of keys
● Selectable global adjacent key suppression (AKS™)
● Selectable sleep duration
● Selectable Max On-Duration values
● Selectable BCD mode
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