PCF8883_1

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 01 — 16 October 2009

7 of 24

NXP Semiconductors

PCF8883

Capacitive proximity switch with auto-calibration

The counter, following the sensor logic depicted in Figure 3, counts the pulses of CUP or

CDN respectively. The counter is reset every time the pulse sequence changes from CUP

to CDN or vice versa. Pin OUT will only be activated when a sufficient number of

consecutive CUP or CDN pulses occur. Low level interference or slow changes in the

input capacitance do not cause the output to switch.

Various measures, such as asymmetrical charge and discharge steps, are taken to

ensure that the output switches off correctly. A special start-up circuit ensures that the

device reaches equilibrium quickly when the supply is attached.

deactivated (short circuit protection) for loads in excess of 30 mA. Pin OUT can also drive

a CMOS input without connection of the external load.

even if no load resistor is connected. This is useful for driving purely capacitive CMOS

inputs. The falling slope can be fairly slow in this mode, depending on load capacitance.

The sampling rate can be adjusted within a specified range by selecting the value of

signal. This prevents interference caused by local AC-fields.

8.1 Output switching modes

The output switching behavior can be selected using pin TYPE (see Figure 5)

capacitive event and deactivated by a following capacitive event.

defined time at each capacitive event. The pulse duration is determined by the value

1 s. Capacitive events are ignored that occur during the time the output is active.

Figure 5 illustrates the switching behavior for the output switching modes. Additionally the

graph illustrates, that short term disturbances on the sensor are suppressed by the circuit.

2.

A capacitive event is a dynamic increase of capacitance at the sensor input pin IN.