E909.01 Datasheet, PDF (32/39 Pages) ELMOS Semiconductor AG – DESIGNING SYSTEMS WITH HALIOS® SWITCH

E909.01
Switch 1:
Switch 2:
Switch 3:
Switch 4:
Parameter: TOTIM
Pretouch time switch 1
Touch accepted
Pretouch time switch 2
Pretouch time switch 3
Touch cancelled
Pretouch time switch 4
Touch accepted
Time
Figure 3.15: Prioritisation of touch events by disabling other touches during the “Pretouch” time
It is also possible to prioritise the switch with the largest signal amplitude to accept the touch. With the parame-
ter SELDELAY (parameter SELDELAY is described in table 2.2) this option can be enabled. In this case the constant
“pretouch” time is extended by a variable part, which is proportional to the signal amplitude. If now several
switches are entering the “pretouch” phase during the same measurement cycle the switch with the largest sig-
nal amplitude will win and activate its touch output.
3.4 Reference Design
The circuit diagram (figure 3.5) below shows an application where the SPI interface is not used in normal opera-
tion. It is, however, possible to activate the SPI interface for test purpose by removing the components RD1, RD3,
RD4, RD5, RD6 and inserting component RD2. In the case of an activated SPI interface the Touch output is not ac-
tive any more.
Due to the synchronous demodulation principle of the HALIOS® regulation loop asynchronous disturbances
outside the modulation frequency band are not critical and do not disturb the measurement. Only synchronous
electrical and optical disturbances can influence the measurement. Thus it is important to avoid electrical cou-
pling of the modulation frequency to the photodiode input and the analogue supply of the E909.01 IC. This can
be avoided by shielding the photodiode connection line with analogue ground, which should be designed like
a grounded coplanar line. Additionally the analogue supply should be decoupled with a lowpass of first order
given in the example by the components R3 and C4.
The ground connection between TCND3000 and E909.01 should be of low resistance type with a ground plane.
ELMOS Semiconductor AG
Application Note
32/39
QM-No.: 03AN0801E.01