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PCA8886TS
Dual channel capacitive proximity switch with auto-calibration and large voltage operating range
1. General descriptionThe PCA8886 is a low power dual channel capacitive proximity switch that uses a
patented (EDISEN) digital method to detect a change in capacitance on remote sensing
plates. Changes in the static capacitance (as opposed to dynamic capacitance changes)
are automatically compensated using continuous auto-calibration. Remote sensing plates
(for example, conductive foil) can be connected directly to the IC1 or remotely using a
coaxial cable.
2. Features and benefits Dynamic proximity switch Digital processing method Automatic calibration Adjustable sensitivity, can be made very high Adjustable response time Wide input capacitance range (10 pF to 60 pF) A large distance (several meters) between the sensing plate and the IC is possible Open-drain output (P-type MOSFET , external load between pin and ground) Output configurable as push-button, toggle, or pulse Wide voltage operating range (VDD = 3 V to 9 V) Designed for battery powered applications (IDD = 6 A, typical) Large temperature operating range (Tamb= 40 C to +85 C) AEC-Q100 compliant for automotive applications Available in TSSOP16
3. Applications Proximity detection Proximity sensing in Door locks and grips Portable entertainment units Computing tablets Switch for medical applications Dashboard: switch to toggle menus and resetting trip counter Switch for use in explosive environments
PCA8886
Dual channel capacitive proximity switch with
auto-calibration and large voltage operating range
Rev. 3 — 14 March 2014 Product data sheet The definition of the abbreviations and acronyms used in this data sheet can be found in Section20.
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration Vandal proof switches Transportation: Switches in or under upholstery, leather, handles, mats, and glass Buildings: switch in or under carpets, glass, or tiles Sanitary applications: use of standard metal sanitary parts (for example, tap) as switch Hermetically sealed keys on a keyboard
4. Ordering information
4.1 Ordering options
5. Marking
Table 1. Ordering information
Table 2. Ordering options
Table 3. Marking codes
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
6. Block diagramNXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
7. Pinning information
7.1 Pinning
7.2 Pin description[1] The internal regulated supply voltage outputs must be decoupled with a decoupling capacitor to VSS[1:2].
Table 4. Pin descriptionInput or input/output pins must always be at a defined level (VSS or VDD) unless otherwise specified.
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
8. Functional descriptionFigure 3 and Figure 4 show the functional principle of one channel of the PCA8886.
The discharge time (tdch) of a chip-internal RC timing circuit, to which the external sensing
plates are connected via pins IN[1:2], 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)[1:2] 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 3).
The pulses control the charge on the external capacitor CCPC on pins CPC[1:2]. 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.
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibrationIf the capacitance on pins IN[1:2] increases, the discharge time tdch increases too.
Therefore it takes longer for the voltage on the corresponding comparator to drop below
Vref. Only once this happens, the comparator output becomes LOW and this results in a
pulse on CDN discharging the external capacitor CCPC slightly. Thus most pulses will now
be given by CUP . Without further action, capacitor CCPC would then fully charge.
However, a chip-internal automatic calibration mechanism that is based on a voltage
controlled sink current (Isink) connected to pins IN[1:2] attempts to equalize the discharge
time tdch with the internal reference discharge time tdch(ref). The current source is
controlled by the voltage on CCPC which causes the capacitance on pins IN[1:2] to be
discharged more quickly in the case that the voltage on CCPC is rising, thereby
compensating for the increase in capacitance on input pins IN[1:2]. This arrangement
constitutes a closed-loop control system that constantly attempts to equalize the
discharge time tdch with tdch(ref). This allows compensating for slow changes in
capacitance on input pins IN[1:2]. Fast changes due to an approaching hand for example
will not be compensated. In the equilibrium state, the discharge times are equal and the
pulses alternate between CUP and CDN.
From this also follows, that an increase in capacitor value CCPC results in a smaller
voltage change per pulse CUP or CDN. Thus the compensation due to internal current
sink source Isink is slower and therefore the sensitivity of the sensor increases. Likewise a
decrease in capacitor CCPC results in a lower sensitivity. (For further information see
Section 14.)
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibrationThe counter, following the sensor logic depicted in Figure 3, counts the pulses of CUP or
CDN respectively. The counter is reset every time the pulse sequence changes from CUP
to CDN or the other way around. Pins OUT[1:2] will only be activated when enough
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.
Pins OUT[1:2] are open-drain outputs capable of pulling an external load Rext
(at maximum current of 20 mA) up to VDD. The load resistor must be dimensioned
appropriately, taking the maximum expected VDD voltage into account. The output will be
automatically deactivated (short circuit protection) for loads in excess of 30 mA. Pins
OUT[1:2] can also drive CMOS inputs without connection of the external load.
A small internal 150 nA current sink Isink enables a full voltage swing to take place on pins
OUT[1:2], 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 (fs) corresponds to half of the frequency used in the RC timing circuit.
The sampling rate can be adjusted within a specified range by selecting the value of
CCLIN. The oscillator frequency is internally modulated by 4 % using a pseudo random
signal. This prevents interference caused by local AC-fields.
8.1 Output switching modesThe output switching behavior can be selected using pins TYPE[1:2] (see Figure5)
Push-button (TYPE[1:2] connected to VSS[1:2]): The output OUT is active as long as
the capacitive event2 lasts.
Toggle (TYPE[1:2] connected to VDD(INTREGD)[1:2]): The output OUT is activated by the
first capacitive event and deactivated by a following capacitive event.
Pulse (CTYPE connected between TYPE[1:2] and VSS[1:2]): The output OUT is
activated for a defined time at each capacitive event. The pulse duration is
determined by the value of CTYPE and is approximately 2.5 ms/nF.
A typical value for CTYPE is 4.7 nF which results in an output pulse duration of about ms. The maximum value of CTYPE is 470 nF which results in a pulse duration of
about1 s. Capacitive events are ignored that occur during the time the output is active.
Figure 5 illustrates the switching behavior for the output switching modes. Additionally the
graph illustrates, that short-term disturbances on the sensor are suppressed by the circuit. A capacitive event is a dynamic increase of capacitance at the sensor input pins IN[1:2].
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
8.2 Voltage regulatorThe PCA8886 implements a chip-internal voltage regulator supplied by pins VDD[1:2] that
provides an internal supply (VDD(INTREGD)), limited to a maximum of 4.6 V. Figure 6 shows
the relationship between VDD[1:2] and VDD(INTREGD)[1:2].
9. Safety notesNXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
10. Limiting values[1] Pass level; Human Body Model (HBM) according to Ref. 7 “JESD22-A114”.
[2] Pass level; Charged-Device Model (CDM), according to Ref. 8 “JESD22-C101”.
[3] Pass level; latch-up testing, according to Ref. 9 “JESD78” at maximum ambient temperature (Tamb(max) =+85 C).
[4] According to the store and transport requirements (see Ref. 12 “UM10569”) the devices have to be stored at a temperature of +8 C to
+45 C and a humidity of 25 % to 75%.
Table 5. Limiting valuesIn accordance with the Absolute Maximum Rating System (IEC 60134).
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
11. Static characteristics[1] When the input capacitance range is limited to 10pF Ci40 pF or an external pull-down resistor RC is used, the device can be
operated down to VDD=3.0 V over the full temperature range.
[2] Idle state is the steady state after completed power-on without any activity on the sensor plate and the voltage on the reservoir capacitor
CCPC settled.
[3] For reliability reasons, the average output current must be limited to 4.6 mA at 70C and 3.0 mA at 85C.
[4] External ceramic chip capacitor recommended (see Figure 15).
Table 6. Static characteristicsVDD = 5 V, Tamb = +25 C; unless otherwise specified.
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
12. Dynamic characteristics
13. Characteristic curves
13.1 Power consumption
Table 7. Dynamic characteristicsVDD = 5 V, CCLIN = 22 pF , CCPC = 470 nF, Tamb = +25 C; unless otherwise specified.
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibrationNXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
13.2 Typical reaction timeNXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
13.3 Reservoir capacitor voltage
NXP Semiconductors PCA8886
Dual channel capacitive proximity switch with auto-calibration
14. Application informationFigure 15 shows the typical connections for a general application3 . The positive supply is
connected to pins VDD[1:2]. It is recommended to connect smoothing capacitors to ground
to both VDD[1:2] and VDD(INTREGD)[1:2] (values for Cdec, see Table6). For further information, see Ref. 2 “AN10832”. Information about the appropriate evaluation board can be found in Ref. 11
“UM10505”.
