QST108 datasheet(14/38 Pages) STMICROELECTRONICS

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Device operating modes

QST108

14/38

4.4.2

Option descriptions

Adjacent key suppression (AKS™)

The QST108 features an adjacent key suppression (AKS™) function.

This function is enabled using the AKS option resistor (OPT2) in standard output mode as

described in Table 4. In BCD output mode, the AKS function is always enabled, regardless

of the option resistor configuration.

Low Power mode option

This option resistor (OPT3) selects whether the device is always sensing the keys or if a low

power consumption phase is introduced between bursts as described in Table 5.

In Low Power mode, a very low consumption (sleep) phase of 100ms is inserted between

the Group B burst and the Group A burst. This significantly reduces the overall consumption

of the device. Sleep duration is not accurate and can vary substantially depending on VDD

and temperature values.

Note:

In Low Power mode, the response time is increased.

Max On-Duration

There are four recalibration timing options (“Max On-Duration”). The recalibration option

resistors (OPT4 and OPT5) control how long it takes for a continuous detection to trigger a

recalibration on a key as described in Table 6. When such an event occurs, only the “stuck”

key is recalibrated.

Table 4.

AKS truth table

OPT2/AKS

Description

VSS

Disabled

VDD

Global locking AKS on all available keys

Table 5.

Low power (LP) mode truth table

OPT3/LP

Description

VSS

Free running mode

VDD

100ms sleep duration

Table 6.

Max On-Duration (MOD) truth table

OPT4/MOD_0

OPT5/MOD_1

Description

VSS

Infinite

VSS

VDD

60s

VDD

VSS

20s

VDD

10s

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