MC33941EG Freescale Semiconductor, MC33941EG Datasheet - Page 7

• Manufacturer Part Number: MC33941EG
• Description: SENSOR, TOUCH/PROXIMITY, EFID, 24SOICW
• Manufacturer: Freescale Semiconductor

Specifications of MC33941EG

• Supply Current: 7mA
• Supply Voltage Range: 9V To 18V
• Sensor Case Style: SOIC
• No. Of Pins: 24
• Operating Temperature Range: -40°C To +110°C
• Svhc: No SVHC (15-Dec-2010)
• Package / Case: SOIC
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FEATURES
SHIELD DRIVER
along wires. This circuit provides a buffered version of the
returned AC signal from the electrode. Since it has nearly the
same amplitude and phase as the electrode signal, there is
little or no potential difference between the two signals,
thereby canceling out any electric field. In effect, the shield
drive isolates the electrode signal from external virtual
grounds. A common application is to connect the Shield
Driver to the shield of a coax cable used to connect an
electrode to the corresponding electrode terminal. Another
typical use is to drive a ground plane that is used behind an
array of touch sensor electrodes in order to cancel out any
virtual grounds that could attenuate the AC signal.
TUNABLE FREQUENCY
the default frequency of 120 kHz, the 33941 has also been
characterized to work in two other frequencies (240 kHz and
60 kHz) for applications with specific needs. These
frequencies are tunable by attaching a 20k and 82k resistor
Sensors
Freescale Semiconductor
A shield driver is included to minimize the electrode signal
The 33941 offers 3 operating frequencies. In addition to
3.5
2.5
1.5
0.5
4
3
2
1
0
0
Figure 4
Output Voltage vs Capacitance at 3 Discrete Frequencies
20
.
Output Voltage vs. Capacitance at 3 Discrete Frequencies
40
60
Capacitance (pF)
80
100
at ROSC respectively. If a wider capacitance range is
needed, simply change the ROSC resistor value to 82k to
have the signal generator operate at 60 kHz which will extend
the capacitance range to 150pF as seen on
figure also shows that one can achieve higher sensitivity at
lower capacitances by setting the ROSC resistor value to
20k. All resistor values listed above are for 5% tolerance
resistors.
ADJUSTABLE RESPONSE TIME
formed by and internal resistor and an external capacitor
attached to LP_CAP. The value of the external capacitor is
selected to allow the designer to optimize the balance
between noise and settling time. A typical value for the
external capacitor is 10nF and in practice it will have a
response time of 1.5ms. If faster response time is required a
1nF capacitor can be used and it will have response times
<
value increases noise accordingly.
200μS. Please note that reducing the LP_CAP capacitor
The rectified sine wave is filtered by a Low Pass Filter
120
140
160
120 kHz
240 kHz
60 kHz
Figure
MC33941
4. The
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