PCF8883USSLASH7EASLASH1 datasheet(6/35 Pages) NXP

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PCF8883

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Product data sheet

Rev. 4.1 — 14 September 2016

6 of 35

NXP Semiconductors

PCF8883

Capacitive touch/proximity switch with auto-calibration

Functional description

Figure 4 and Figure 5 show the functional principle of the PCF8883.

The discharge time (tdch) of a chip-internal RC timing circuit, to which the external sensing

plate is connected via pin IN, is compared to the discharge time (tdch(ref)) of a second

chip-internal reference RC timing circuit. Both RC timing circuits are periodically charged

from VDD(INTREGD) via identical switches and then discharged via a resistor to ground

(VSS). Both switches are synchronized.

The charge-discharge cycle is governed by the sampling rate (fs). If the voltage of one of

the RC timing circuits falls below the internal reference voltage Vref, the respective

comparator output becomes LOW. The logic following the comparators determines which

comparator switches first. If the upper (reference) comparator switches, then a pulse is

given on CUP. If the lower (input) comparator switches first, then a pulse is given on CDN

(see Figure 4).

The pulses control the charge on the external capacitor CCPC on pin CPC. Every time a

pulse is given on CUP, capacitor CCPC is charged from VDD(INTREGD) for a fixed time

causing the voltage on CCPC to rise. Likewise when a pulse occurs on CDN, capacitor

CCPC is connected to a current sink to ground for a fixed time causing the voltage on CCPC

to fall.

Fig 4.

Functional diagram of the sensor logic

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