PCF8883T datasheet(16/24 Pages) NXP

16 / 24 page

PCF8883_1

Product data sheet

Rev. 01 — 16 October 2009

16 of 24

NXP Semiconductors

PCF8883

Capacitive proximity switch with auto-calibration

13. Application information

Figure 15 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 5).

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 provided that

an additional discharge resistor RC is placed as shown in Figure 15. Resistor RC simply

reduces the discharge time such that the internal timing requirements are fulﬁlled.

For further information see Ref. 2 “AN10832”. Information about the appropriate evaluation board can be found in Ref. 11

“UM10370”.

CSENS = sensing plate capacitance.

The coaxial cable is optional.

Fig 15. Typical application

VDD

VDD(INTREGD)

OUT

TYPE

CLIN

VSS

CSENS

PCF8883

VDD(INTREGD)

Push-

button

Pulse

Toggle

CPC

013aaa079

COAXIAL CABLE

SENSING PLATE

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