PCF8883T NXP [NXP Semiconductors], PCF8883T Datasheet - Page 5

• 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
8. Functional description
PCF8883_1
Product data sheet
Figure 3
(t
via pin IN, is compared to the discharge time (t
RC timing circuit. Both RC timing circuits are periodically charged from V
identical switches and then discharged via a resistor to ground (V
synchronized.
The charge-discharge cycle is governed by the sampling rate (f
the RC timing circuits falls below the internal reference voltage V
comparator output will become 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
The pulses control the charge on the external capacitor C
pulse is given on CUP, capacitor C
causing the voltage on C
C
to fall.
Fig 3.
dch
CPC
) of a chip-internal RC timing circuit, to which the external sensing plate is connected
is connected to a current sink to ground for a fixed time causing the voltage on C
and
Functional diagram of the sensor logic
Figure
IN
Figure 4
f
s
3).
Rev. 01 — 16 October 2009
show the functional principle of the PCF8883. The discharge time
V
DD(INTREGD)
CPC
to rise. Likewise when a pulse occurs on CDN, capacitor
V
CPC
ref
I
sink
Capacitive proximity switch with auto-calibration
is charged from V
&
&
V
SS
dch(ref)
V
CUP
CDN
DD(INTREGD)
) of a second chip-internal reference
CPC
DD(INTREGD)
CPC
on pin CPC. Every time a
s
). If the voltage of one of
ref
SS
, the respective
). Both switches are
COUNTER
LOGIC
for a fixed time
013aaa093
PCF8883
© NXP B.V. 2009. All rights reserved.
DD(INTREGD)
5 of 24
via
CPC