pca8885 NXP Semiconductors, pca8885 Datasheet - Page 35

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

NXP Semiconductors
19. Test information
PCA8885
Objective data sheet
19.1 Quality information
Figure 25
simplicity, the sensors attached to the secondary-chip are not shown in this diagram. The
sensors of the secondary-chip can be arranged independently of the sensors of the
primary-chip or combined in a common larger matrix.
Both chips use different I
The primary-chip has A0 connected to ground; the secondary-chip has A0 connected to
V
In this case, the primary-chip is programmed to use the internal oscillator as clock
reference. The primary-chip is also programmed to enable the clock output. The
secondary-chip is programmed to use the clock output from the primary-chip as input
clock. The internal oscillator of the secondary-chip is shut down to save power in this
mode.
The interrupt output INT of the primary-chip is routed to the INT_IN input of the
secondary-chip, where it is OR’ed with the interrupt state of the secondary-chip.
The sensing plate capacitances may consist of a small metal area, for example behind an
isolating layer. Illustrated in
a sensor touch always excites two sensor plates at the same time.
The sensing plates are connected to a coaxial cable (for remote sensors) or a shielded
connection, which in turn is connected to the input pin IN. The connection capacitance
contributes to the input capacitance and must not be neglected. An internal low pass filter
(not shown) is used to reduce RF interference. An additional low pass filter consisting of a
resistor RF and capacitor CF can be added to the input to improve RF immunity further
than required. For good performance, the total amount of capacitance on the input
(C
Even if the external filtering is not required, placing C
capacitance to an optimal value. These conditions allow the control loop to adapt to the
static capacitance on C
capacitance. A higher capacitive input loading is possible, if an additional discharge
resistor RC is used. Resistor RC simply reduces the discharge time such that the internal
timing requirements can be fulfilled.
The sensitivity of the sensors can be influenced by the sensing plate area and capacitors
C
sensitivity is desired, C
interference. The CPCx pins have high impedance and are sensitive to leakage currents.
Therefore C
type.
For the choice of proper component values for a given application, the component
specifications in
This product has been qualified in accordance with the Automotive Electronics Council
(AEC) standard Q100 - Failure mechanism based stress test qualification for integrated
circuits, and is suitable for use in automotive applications.
DD(ext)
CPC
s
+ C
. The sensitivity is significantly reduced when C
. In this way, each circuit is addressed individually.
CABLE
shows the typical connections for a general application using two chips. For
CPC
+ C
All information provided in this document is subject to legal disclaimers.
should be a high-quality foil or ceramic capacitor, for example an X7R
Section 16 on page 26
F
) should be in the proper range, the optimum point being around 30 pF.
Rev. 1 — 24 November 2011
CPC
S
2
and to compensate for slow changes in the sensing plate
C addresses programmed by the voltage level applied to pin A0.
Capacitive 8-channel proximity switch with auto-calibration
can be increased, but it also increases sensitivity to
Figure 25
is a 4  4 sensor arrangement. In this configuration,
must be followed.
CPC
F
can help to bring the input
is reduced. When maximum
PCA8885
© NXP B.V. 2011. All rights reserved.
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