QST108 datasheet(12/38 Pages) STMICROELECTRONICS

12 / 38 page

Device operating modes

QST108

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4.3

Burst operation

The device operates in “Burst” mode. Each key touch is acquired using a burst of charge-

transfer sensing pulses whose count varies depending on the value of the sense capacitor

CS and the load capacitance CX. Key touches are acquired using two successive bursts of

pulses:

●

Burst A: Keys 1, 2, 3, and 4

●

Burst B: Keys 5, 6, 7, and 8

Bursts always operate in an A-B sequence. If Keys 5 to 8 are not implemented, the QST

device will not perform the Burst B to improve the response time and reduce the power

consumption when in Low Power (LP) mode.

In Low Power mode, the device sleeps in an ultra-low current state between bursts to

conserve power.

4.4

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).

4.4.1

Main features

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Pins KOUT1 to KOUT8 directly reflect the state of keys

●

Selectable global adjacent key suppression (AKS™)

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Selectable sleep duration

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Selectable Max On-Duration values

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Selectable BCD mode

QST108 Datasheet(PDF) 12 Page - STMicroelectronics