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Freescale Semiconductor Technical Data
Document Number: MC33941 Rev. 3, 11/2006
Electric Field Imaging Device
The MC33941 is intended for cost-sensitive applications where non-contact sensing of objects is desired. When connected to external electrodes, an electric field is created. The MC33941 detects objects in this electric field. The IC generates a low-frequency sine wave, which is adjustable by using an external resistor and is optimized for 120 kHz. The sine wave has very low harmonic content to reduce harmonic interference. The MC33941 also contains support circuits for a microcontroller unit (MCU) to allow the construction of a two-chip E-field system. Features * * * * * * * * Supports up to 7 Electrodes Shield Driver for Driving Remote Electrodes Through Coaxial High-Purity Sine Wave Generator Tunable with External Resistor Response Time Tunable with External Capacitor +5V Regulator to Power External Circuit Can support up to 28 touch pad sensors (2 way multiplexing) Extended Temperature Range 0 to 110oC Pb-Free and RoHS compliant
EG SUFFIX (Pb-FREE) 24-TERMINAL SOICW CASE 751E-04
MC33941
ELECTRONIC FIELD IMAGING DEVICE
Typical Applications * * * * * * * * * * * * * Appliance Control Panels and Touch Sensors Linear and Rotational Sliders Spill Over Flow Sensing Measurement Refrigeration Frost Sensing Industrial Control and Safety Systems Security Proximity Detection for Wake-Up Features Touch Screens Garage Door Safety Sensing PC Peripherals Patient Monitoring Point of Sale Terminals Size Detection Liquid Level Sensing ORDERING INFORMATION
Device Name MC33941EG/R2 Temperature Range 0 to 110C Drawing 98ASB42564B Package SOICW-24
DGND N/C SHIELDEN C B A LEVEL LPCAP ROSC VDDCAP VPWR VCCCAP
N/C E7 E6 E5 E4 E3 E2 E1 TEST GND SHIELD AGND
Pin Connections
(c) Freescale Semiconductor, Inc., 2006. All rights reserved.
A,B,C
3
CONTROL LOGIC
2.8 k E1-E7 2.8 k MUX OUT
OSC
22 k (Nominal)
ROSC
SHIELDEN 150
700
MUX IN
SHIELD
700
RECT LPCAP
VCCCAP VDDCAP VCC REG VDD REG
LPF
GAIN AND OFFSET LEVEL
VPWR
AGND GND
Figure 1. Simplified Functional Block Diagram
MC33941 2 Sensors Freescale Semiconductor
Table 1. Maximum Ratings All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent damage to the device.
Rating ELECTRICAL RATINGS Peak VPWR Voltage Double Battery 1 Minute Maximum TA = 30C ESD Voltage Human Body Model (CZAP = 100 pF, RZAP = 1500 W) Machine Model (CZAP = 200 pF, RZAP = 0 W) Charge Device Model (CDM), Robotic (CZAP = 4.0pF) THERMAL RATINGS Storage Temperature Operating Ambient Temperature Operating Junction Temperature Thermal Resistance Junction-to-Ambient (1) Junction-to-Case (2) Junction-to-Board (3) Soldering Temperature (4) Notes 1. Junction temperature is a function of on-chip power dissipation, package thermal resistance, mounting site (board) temperature, ambient temperature, air flow, power dissipation of other components on the board, and board thermal resistance. In accordance with SEMI G3887 and JEDEC JESD51-2 with the single layer board horizontal. 2. Indicates the average thermal resistance between the die and the case top surface as measured by the cold plate method (MILSPEC 883 Method 1012.1) with the cold plate temperature used for the case temperature. 3. Thermal resistance between the die and the printed circuit board per JEDEC JESD51-8. Board temperature is measured on the top surface of the board near the package. 4. Terminal soldering temperature limit is for 10 seconds maximum duration. The device is not designed for immersion soldering. Exceeding these limits may cause malfunction or permanent damage to the device. TSTG TA TJ RJA RJC RJB -55 to 150 -0 to 110 -0 to 150 41 0.2 3.0 C C C C/W VESD VPWRPK VDBLBAT 26.5 V 2000 200 1200 40 V V Symbol Value Unit
MC33941 Sensors Freescale Semiconductor 3
Table 2. Static Electrical Characteristics Characteristics noted under conditions 5.5 V VSUP 18 V, 0C TA 110C, GND = 0 V unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions unless otherwise noted.
Characteristic SUPPLY (VPWR) Supply Voltage IDD (VPWR = 14V) (Quiescent supply current measured over temperature. Assumes that no external devices connected to internal voltage regulators) VOLTAGE REGULATOR 5V Regulator Voltage 7.0 V VPWR 18 V, 1.0 mA IL 75 mA, CFILT = 47 F ELECTRODE SIGNALS (E1-E7) Total Variance Between Electrode Measurements (5) All CLOAD = 15 pF Electrode Maximum Harmonic Level Below Fundamental 5.0 pF CLOAD 150 pF Electrode Transmit Output Range 5.0 pF CLOAD 150 pF Receive Input Voltage Range Grounding Switch on ISW = 1.0 mA LOGIC I/O (C, B, A) CMOS Logic Input Low Threshold Logic Input High Threshold Voltage Hysteresis Input Current VIN = VCC VIN = 0 V SIGNAL DETECTOR (LPCAP) Detector Output Resistance LPCAP to LEVEL Gain LPCAP to LEVEL Offset DETRO AREC VRECOFF - 3.6 -3.3 50 4.0 -3.0 - 4.4 -2.7 k AV V VTHL VTHH VHYS IIN 10 -5.0 - - 50 5.0 0.3 - - - - 0.06 - 0.7 - VCC VCC VCC A Voltage(6) RXV SWVON - - 5.0 ELTXV 1.0 0 - - 8.0 9.0 V V
(5)
Symbol
Min
Typ
Max
Unit
VPWR IDD
9.0
12
18
V mA
6.0
7.0
8.0
VCCCAP 4.75 5 5.25
V
ELVVAR - ELHARM - -20 - - 3.0
%
dB
V
Notes 5. Verified by design and characterization. Not tested in production. 6. Current into grounded terminal under test = 1.0 mA.
MC33941 4 Sensors Freescale Semiconductor
Table 3. Dynamic Electrical Characteristics (7) Characteristics noted under conditions 5.5 V VSUP 18 V, 0C TA 110C, GND = 0 V unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions unless otherwise noted.
Characteristic OSC (ROSC) OSC Frequency Stability OSC Center Frequency ROSC = 39 k ROSC = 20 k ROSC = 82 k Harmonic Content 2nd through 4th Harmonic Level 5th and Higher SHIELD DRIVER (SHIELD) Shield Driver Maximum Harmonic level below Fundamental 10 pF CLOAD 500 pF Shield Driver Gain Bandwidth Product Measured at 120 kHz Notes 7. All parameters are guaranteed by design. SDGBW - 4.5 - SDHARM - -20 - MHz dB f STAB f OSC - - - - - 120 240 60 10 - - - dB - - - - -20 -60 % kHz Symbol Min Typ Max Unit
OSCHARM
MC33941 Sensors Freescale Semiconductor 5
PRINCIPLE OF OPERATION
The 33941 generates a low radio frequency sine wave with nominal 5.0 V peak-to-peak amplitude. The frequency is set by an external resistor and is optimized for 120 kHz. An internal multiplexer routes the signal to one of the 7 terminals under control of the ABC input terminals. A receiver multiplexer simultaneously connected to the selected electrode and routes its signal to a detector, which converts the sine wave to a DC level. The DC level is filtered by an external capacitor, is multiplied and offset to increase sensitivity. All electrode outputs are grounded internally by the device when not selected. The amplitude and phase of the sinusoidal wave at the electrode are affected by objects in proximity. A "capacitor" is formed between the driving electrode and the object, each forming a "plate" that holds the electric charge. The voltage measured is an inverse function of the capacitance between the electrode being measured, the surrounding electrodes, and other objects in the electric field surrounding the electrode. Increasing capacitance results in decreasing voltage. The value of the series resistor (22kohm) was chosen to provide a near linear relationship at 120 kHz over a range of 10pF to 70pF. While exploring applications using the E-Field chip, it is always useful to approach the problem using the capacitor model.
Drive level ~ 5 v p-p Load Resistor (22 K ohms) Stray Variable Capacitance
Voltage Level Proportional to 1/C (voltage divider)
Detector
Low Pass Filter
Electrodes Object
Sine Generator (120 KHz)
Detected Signal Level Decreases with Increasing Capacitance
Virtual Ground
Capacitance increases as electrodes move closer together Capacitor Model
Figure 2. Conceptual Block Diagram CAPACITOR MODEL The capacitance measured by the E-Field IC is: Proportional to the area of the electrode Proportional to the dielectric constant of the material between the electrodes * Inversely proportional to the distance between the objects * * Table 4 Dielectric Constants of Various Materials
Dielectric Material Acrylic Glass Nylon Plastic Polyester Film Thickness (mil) 84.5 74.5 68 10 9 k 2.4-4.5 7.5 3.0-5.0 3.2 2.8-4.5 1 80 3.2 2.1
k A C= 0 d
Flexible Vinyl Film
C
k
d
Air Water Ice Automotive Oil
C=The Capacitance in Farads (F) A=The area of the plates in square meters (m2) d=The distance between the plates in meters (m) k=The dielectric constant of the material separating the plates 0=Is the permittivity of free space (8.85 x 10-12 F/m)
Figure 3. Capacitor Model MC33941 6 Sensors Freescale Semiconductor
FEATURES
SHIELD DRIVER A shield driver is included to minimize the electrode signal 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 33941 offers 3 operating frequencies. In addition to 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 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 4. The 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 The rectified sine wave is filtered by a Low Pass Filter 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 < 200uS. Please note that reducing the LP_CAP capacitor value increases noise accordingly.
Output Voltage vs Capacitance at 3 Discrete Frequencies
4 3.5 Voltage Output (Volts) 3 2.5 2 1.5 1 0.5 0 0 20 40 60 80 100 120 140 160 Capacitance (pF) 120 kHz 240 kHz 60 kHz
Figure 4. Output Voltage vs. Capacitance at 3 Discrete Frequencies
MC33941 Sensors Freescale Semiconductor 7
BASIC CONNECTIONS
PIN DESCRIPTIONS Table 6. Pin Description
Pin Number
DGND N/C SHIELDEN C B A LEVEL LPCAP ROSC VDDCAP VPWR VCCCAP N/C E7 E6 E5 E4 E3 E2 E1 TEST GND SHIELD AGND
Pin Name DGND N/C SHIELDEN C, B, A LEVEL
Definition Connected to the ground return These pins should be left open. Used to enable the shield signal Controls electrode or reference activity This is the detected, amplified, and offset representation of the signal voltage on the selected electrode A capacitor on this pin forms a low pass filter with the internal series resistance from the detector to this pin A resistor from this pin to circuit ground determines the operating frequency of the oscillator A 47F capacitor is connected to this pin to filter the internal analog regulated supply 12 V power applied to this pin will be converted to the internal regulated voltages needed to operate the part A 47F capacitor is connected to this pin and VCCCAP provides a regulated 5.0 V to power external circuits 75 mA Max Connected to the ground return of the analog circuitry Connects to cable shields to cancel cable capacitance. Main IC ground Connect to circuit ground Electrode pins
1 2, 24 3 4,5,6 7
8
LPCAP
Figure 5. Pin Descriptions Table 5. Electrode Selection
Terminal/SIGNAL No electrodes selected E1 E2 E3 E4 E5 E6 E7 C 0 0 0 0 1 1 1 1 B 0 0 1 1 0 0 1 1 A 0 1 0 1 0 1 0 1
9
ROSC
10
VDDCAP
11
VPWR
12
VCCCAP
13 14 15 16 17-23
AGND SHIELD GND TEST E1-E7
+5V MC33941
VCCCAP
47uF
ROSC
39k
VDDCAP MCU Power Analog In
47uF
LPCAP
10nF
LEVEL
3
Electrode Select Shield Enable
+12V
A, B, C SHIELDEN
E1 Field Electrodes (E1 through E7) E7 SHIELD
VPWR TEST AGND GND
Figure 6. Simplified Application Diagram MC33941 8 Sensors Freescale Semiconductor
PACKAGE DIMENSIONS
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EG SUFFIX CASE 751E-04 ISSUE F
MC33941 Sensors Freescale Semiconductor 9
PACKAGE DIMENSIONS
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EG SUFFIX CASE 751E-04 ISSUE F
MC33941 10 Sensors Freescale Semiconductor
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MC33941 Rev. 3 11/2006

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