QST108 datasheet(14/51 Pages) STMICROELECTRONICS

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Device operating modes

QST108

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Free run in detect

The behavior in this mode is the same as in the standard low power mode except that

the sleep window insertion is always skipped if any of the active keys is detected as

touched.

This is useful to improve the wheel response time.

●

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.

Caution:

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 QST108 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 8 output pins reflect the status of the 8 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

five general-purpose outputs.

Table 3.

Operating modes

OPT1: Mode selection

Option resistor function

OPT2

OPT3

OPT4

OPT5

OPT6

Pin OPT1 is high at start-up Stand-alone mode

AKS

MOD_0 MOD_1

Pin OPT1 is low at start-up

I2C mode

ADD0

ADD1

ADD2

Unused Unused

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