SX8663 datasheet(44/64 Pages) SEMTECH

44 / 64 page

ADVANCED COMMUNICATIONS & SENSING

Rev5 4

th August 2011

www.semtech.com

SX8663

Capacitive Button Matrix (up to 36) and Proximity Controller

with Individual LED Drivers and Buzzer Output

BtnAvgPosThresh. This mechanism avoids that a valid touch will be averaged and finally the tick difference

becomes zero.

In case three or more sensors reach the BtnAvgPosThresh value simultaneously then the SX8663 will start an

offset compensation procedure.

Small environmental and system noise cause the ticks to vary slowly around the zero idle mode value.

In case the ticks get slightly negative this is considered as normal operation. However large negative values will

trigger an offset compensation phase and a new set of DCVs will be obtained.

The decision to trigger a compensation phase based on negative ticks is determined by the value in the register

BtnCompNegThresh and by the number of ticks below the negative thresholds defined in register

BtnCompNegCntMax. An example is shown in Figure 46.

Figure 46

Negative Ticks Offset Compensation Trigger

BtnCompNegThresh

Small negative ticks are considered as normal operation and will occur very often.

Larger negative ticks however need to be avoided and a convenient method is to trigger an offset

compensation phase. The new set of DCV will assure the idle ticks will be close to zero again.

A trade-off has to be found for the value of this register. A negative threshold too close to zero will trigger a

compensation phase very often. A very negative threshold will never trigger.

BtnCompNegCntMax

As soon as the ticks get smaller than the Negative Threshold the Negative Counter starts to count.

If the counter goes beyond the Negative Counter Max then the offset compensation phase is triggered.

The recommended value for this register is ‘1’ which means that the offset compensation starts on the first tick

below the negative threshold.

BtnHysteresis

The hysteresis percentage is identical for all buttons.

A touch is detected if the ticks are getting larger as the value defined by:

CapThreshold + CapThreshold * hysteresis.

A release is detected if the ticks are getting smaller as the value defined by:

CapThreshold - CapThreshold * hysteresis.

BtnStuckAtTimeout

The stuckat timer can avoid sticky buttons.

If the stuckat timer is set to one second then the touch of a finger will last only for one second and then a

compensation will be performed and button hence considered released, even if the finger remains on the

button for a longer time. After the actual finger release the button can be touched again and will be reported as

usual. In case the stuckat timer is not required it can be set to zero.

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