PCF8883

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© NXP Semiconductors N.V. 2016. All rights reserved.

Product data sheet

Rev. 4.1 — 14 September 2016

17 of 35

NXP Semiconductors

PCF8883

Capacitive touch/proximity switch with auto-calibration

14. Application information

Figure 16 shows the typical connections for a general application3. The positive supply is

connected to pin VDD. It is recommended to connect smoothing capacitors to ground to

both VDD and VDD(INTREGD) (values for Cdec, see Table 6).

The sampling rate is determined by the capacitance CCLIN on pin CLIN. A higher sampling

rate reduces the reaction time and increases the current consumption.

The sensing plate capacitance CSENS may consist of a small metal area, for example

behind an isolating layer. The sensing plate can be connected to a coaxial cable (CCABLE)

which in turn is connected to the input pin IN. Alternatively, the sensing plate can be

directly connected to the input pin IN. An internal low pass filter is used to reduce RF

interference. An additional low pass filter consisting of a resistor RF and capacitor CF can

be added to the input to further improve RF immunity as required. For good performance,

the total amount of capacitance on the input (CSENS +CCABLE +CF) should be in the

proper range, the optimum point being around 30 pF. These conditions allow the control

loop to adapt to the static capacitance on CSENS and to compensate for slow changes in

the sensing plate capacitance. A higher capacitive input loading is possible if an additional

discharge resistor RC is placed as shown in Figure 16. Resistor RC simply reduces the

discharge time such that the internal timing requirements are fulfilled.

The sensitivity of the sensor can be influenced by the sensing plate area and capacitor

CCPC. The sensitivity is significantly reduced when CCPC is reduced. When maximum

sensitivity is desired CCPC can be increased, but this also increases sensitivity to

interference. Pin CPC has high-impedance and is sensitive to leakage currents.

3.

For further information, see Ref. 4 “AN10832”. Information about the appropriate evaluation board can be found in Ref. 13

“UM10370”.

CSENS = sensing plate capacitance.

The coaxial cable is optional.

Fig 16. Typical application