pca8885 NXP Semiconductors, pca8885 Datasheet - Page 6

• Manufacturer Part Number: pca8885
• Description: Capacitive 8-channel Proximity Switch With Auto-calibration And Very Low Power Consumption
• Manufacturer: NXP Semiconductors

NXP Semiconductors
8. Functional description
PCA8885
Objective data sheet
Fig 3.
Fig 4.
CLK
TA0
TA1
TA2
TA8
IN0
sampling
Timing diagram of sensor sampling
Functional diagram of sensor operation
SENSING PLATE
SENSING PLATE
125 μs
IN1
sampling
The sensing plate have to be connected to the sensor input pins INx. The discharge times
(t
RC timing element. This is done sequentially for each sensor input pin. The RC timing
circuits are periodically charged from V
V
The channels are sampled sequentially, while the reference element is activated at the
sampling point of each channel (see timing diagram in
IN0
IN7
dch
SS
. The charge-discharge cycle for each channel is governed by the sampling rate (f
.......................................................................................................
) on the sensor input pins, are compared to the discharge time (t
TAref
TA0
TA7
V
V
V
t dch0
t
t dch(ref)
dch7
DD(INTREGD)
DD(INTREGD)
DD(INTREGD)
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 24 November 2011
V
Capacitive 8-channel proximity switch with auto-calibration
ref
1 ms
TIMING REF
UP
DOWN
UP
DOWN
CUP
CDN
CUP
CDN
DD(INTREGD)
V
V
DD(INTREGD)
DD(INTREGD)
and then discharged via a resistor to
CTR
LOGIC
CTR
LOGIC
Figure
CHANNEL 0
CHANNEL 7
IN7
sampling
OUT0
OUT7
3).
IN0
sampling
CPC0
CPC7
dch(ref)
PCA8885
© NXP B.V. 2011. All rights reserved.
013aaa226
) of an internal
C CPC0
C CPC7
013aaa227
6 of 43
s
).