sx8675iwltrt Semtech Corporation, sx8675iwltrt Datasheet - Page 31

• Manufacturer Part Number: sx8675iwltrt
• Description: Haptics Enabled Multitouch 4/5-wire Resistive Touchscreen Controller With Proximity Sensing
• Manufacturer: Semtech Corporation

SX8674/SX8675/SX8676
Haptics Enabled Multitouch 4/5-Wire
Resistive Touchscreen Controller with Proximity Sensing
ADVANCED COMMUNICATIONS & SENSING
5.3.4
PROXAVG Update
PROXAVG update consists in averaging PROXUSEFUL to ignore its “fast” variations (i.e. user finger/palm/hand)
and extract only the very slow variations of environment capacitance C
.
Env
One can program positive and negative debounced thresholds (PROXAVGPOSTHRESH/PROXAVGPOSDEB
and PROXAVGNEGTHRESH/PROXAVGNEGDEB) within which PROXAVG can vary without triggering
compensation (ie small acceptable environment drift).
Large positive values of PROXUSEFUL are considered as normal (user finger/hand/head) but large negative
values are considered abnormal and should be compensated quickly. For this purpose, the averaging filter
coefficient can be set independently for positive and negative variations via PROXAVGPOSFILT and
PROXAVGNEGFILT. Typically we have PROXAVGPOSFILT > PROXAVGNEGFILT to filter out (abnormal)
negative events faster.
To prevent PROXAVG to be “corrupted” by user activity (should only reflect environmental changes) it is freezes
when proximity is detected.
Figure 38 – ProxAvg vs Proximity Event
th
Rev 1 – 25
July 2011
31
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