PCF8883T NXP [NXP Semiconductors], PCF8883T Datasheet - Page 7

• Manufacturer Part Number: PCF8883T
• Description: Capacitive proximity switch with auto-calibration, large voltage operating range and very low power consumption
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
2.
PCF8883_1
Product data sheet
A capacitive event is a dynamic increase of capacitance at the sensor input pin IN.
8.1 Output switching modes
The counter, following the sensor logic depicted in
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.
Pin OUT is an open-drain output capable of pulling an external load R
current of 20 mA) up to V
the maximum expected V
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.
A small internal 150 nA current sink I
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 (f
The sampling rate can be adjusted within a specified range by selecting the value of
C
signal. This prevents interference caused by local AC-fields.
The output switching behavior can be selected using pin TYPE (see
A typical value for C
10 ms. The maximum value of C
1 s. Capacitive events are ignored that occur during the time the output is active.
Figure 5
graph illustrates, that short term disturbances on the sensor are suppressed by the circuit.
•
•
•
CLIN
Push-button (TYPE connected to V
capacitive event
Toggle (TYPE connected to V
capacitive event and deactivated by a following capacitive event.
Pulse (C
defined time at each capacitive event. The pulse duration is determined by the value
of C
. The oscillator frequency is internally modulated by 4 % using a pseudo random
TYPE
illustrates the switching behavior for the output switching modes. Additionally the
TYPE
and is approximately 2.5 ms/nF.
connected between TYPE and V
TYPE
s
2
) corresponds to half of the frequency used in the RC timing circuit.
lasts.
Rev. 01 — 16 October 2009
is 4.7 nF which results in an output pulse duration of about
DD
DD
. The load resistor must be dimensioned appropriately, taking
voltage into account. The output will be automatically
TYPE
DD(INTREGD)
sink
Capacitive proximity switch with auto-calibration
is 470 nF which results in a pulse duration of about
SS
enables a full voltage swing to take place on OUT,
): The output OUT is active as long as the
): The output OUT is activated by the first
SS
Figure
): The output OUT is activated for a
3, counts the pulses of CUP or
Figure
ext
PCF8883
© NXP B.V. 2009. All rights reserved.
(at maximum
5)
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