Freescale Semiconductor Technical Data Document number: MC34940 Rev 4, 11/2006 Electric Field Imaging Device The MC34940 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 MC34940 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 MC34940 also contains support circuits for a microcontroller unit (MCU) to allow the construction of a two-chip E-field system. MC34940 ELECTRONIC FIELD IMAGING DEVICE 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 Can support up to 28 touch pad sensors Pb-Free and RoHS compliant Typical Applications • • • • • • • • • • • • • EG SUFFIX (Pb-FREE) 24-TERMINAL SOICW CASE 751E-04 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 DGND E7 SHIELDEN E6 C E5 B E4 A E3 LEVEL E2 LPCAP E1 ROSC VDDCAP VPWR VCCCAP ORDERING INFORMATION Device Name Temperature Range Drawing Package MC34940EG/R2 0 to 90°C CASE 751E-04 SOICW-24 © Freescale Semiconductor, Inc., 2006. All rights reserved. N/C N/C Pin Connections TEST GND SHIELD AGND 3 A,B,C CONTROL LOGIC 2.8 kΩ E1-E7 ROSC OSC 2.8 kΩ MUX OUT 22 kΩ (Nominal) SHIELDEN 150 Ω 700Ω MUX IN SHIELD RECT 700Ω LPF VCCCAP LPCAP VDDCAP VPWR VCC REG AGND VDD REG GAIN AND OFFSET LEVEL GND Figure 1. Simplified Functional Block Diagram MC34940 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 Symbol Value Unit 40 V ELECTRICAL RATINGS Peak VPWR Voltage VPWRPK Double Battery 1 Minute Maximum TA = 30°C VDBLBAT ESD Voltage Human Body Model (CZAP = 100 pF, RZAP = 1500 Ω) Machine Model (CZAP = 200 pF, RZAP = 0 Ω) Charge Device Model (CDM), Robotic (CZAP = 4.0 pF) VESD V 26.5 V ±2000 ±200 ±1200 THERMAL RATINGS Storage Temperature TSTG -55 to 150 °C Operating Ambient Temperature TA -0 to 90 °C Operating Junction Temperature TJ -0 to 150 °C Thermal Resistance Junction-to-Ambient (1) Junction-to-Case (2) Junction-to-Board (3) RθJA RθJC RθJB 41 0.2 3.0 Soldering Temperature (4) TSOLDER 260 °C/W °C Notes 1. 2. 3. 4. 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 G38-87 and JEDEC JESD51-2 with the single layer board horizontal. 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. 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. 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. MC34940 Sensors Freescale Semiconductor 3 Table 2. Static Electrical Characteristics Characteristics noted under conditions 5.5 V ≤ VSUP ≤ 18 V, 0°C ≤ TA ≤ 90°C, GND = 0 V unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25°C under nominal conditions unless otherwise noted. Characteristic Symbol Min Typ Max 9.0 12 18 6.0 7.0 8.0 – – 3.0 – -20 – 1.0 – 8.0 0 – 9.0 – – 5.0 Unit SUPPLY (VPWR) Supply Voltage VPWR IDD (VPWR = 14 V) (Quiescent supply current measured over temperature. Assumes that no external devices connected to internal voltage regulators) IDD V mA ELECTRODE SIGNALS (E1–E7) Total Variance Between Electrode Measurements (5) All CLOAD = 15 pF ELVVAR Electrode Maximum Harmonic Level Below Fundamental (5) 5.0 pF ≤ CLOAD ≤ 150 pF ELHARM Electrode Transmit Output Range 5.0 pF ≤ CLOAD ≤ 150 pF ELTXV Receive Input Voltage Range Grounding Switch on Voltage ISW = 1.0 mA RXV (6) SWVON % dB V V V LOGIC I/O (C, B, A) CMOS Logic Input Low Threshold VTHL 0.3 – – VCC Logic Input High Threshold VTHH – – 0.7 VCC Voltage Hysteresis VHYS – 0.06 – VCC 10 -5.0 – – 50 5.0 DETRO – 50 – kΩ LPCAP to LEVEL Gain AREC 3.6 4.0 4.4 AV LPCAP to LEVEL Offset VRECOFF -3.3 -3.0 -2.7 V Input Current VIN = VCC VIN = 0 V IIN µA SIGNAL DETECTOR (LPCAP) Detector Output Resistance Notes 5. Verified by design and characterization. Not tested in production. 6. Current into grounded terminal under test = 1.0 mA. MC34940 4 Sensors Freescale Semiconductor Table 3. Dynamic Electrical Characteristics Characteristics noted under conditions 5.5 V ≤ VSUP ≤ 18 V, 0°C ≤ TA ≤ 90°C, GND = 0 V unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25°C under nominal conditions unless otherwise noted. Characteristic Symbol Min Typ Max Unit OSC Frequency Stability f STAB – – 10 % OSC Center Frequency ROSC = 39 kΩ ROSC = 20 kΩ ROSC = 82 kΩ f OSC – – – 120 240 60 – – – – – – – -20 -60 – -20 – – 4.5 – OSC (ROSC) Harmonic Content 2nd through 4th Harmonic Level 5th and Higher OSCHARM kHz dB SHIELD DRIVER (SHIELD) Shield Driver Maximum Harmonic level below Fundamental 10 pF ≤ CLOAD ≤ 500 pF SDHARM Shield Driver Gain Bandwidth Product Measured at 120 kHz SDGBW dB MHz MC34940 Sensors Freescale Semiconductor 5 PRINCIPLE OF OPERATION The MC34940 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 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 Drive level ~ 5 V p-p 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 (22 kΩ) was chosen to provide a near linear relationship at 120 kHz over a range of 10 pF to 70 pF. While exploring applications using the E-Field chip, it is always useful to approach the problem using the capacitor model. Voltage Level Proportional to 1/C (voltage divider) Load Resistor (22 kΩ) Detector Stray Variable Capacitance Electrodes Object Low Pass Filter Detected Signal Level Decreases with Increasing Capacitance Sine Generator (120 kHz) Capacitance increases as electrodes move closer together Virtual Ground 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 • • kε A C= 0 d C k d 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) Table 4. Dielectric Constants of Various Materials Dielectric Material Thickness (mil) k Acrylic 84.5 2.4-4.5 Glass 74.5 7.5 Nylon Plastic 68 3.0-5.0 Polyester Film 10 3.2 Flexible Vinyl Film 9 2.8-4.5 Air - 1.0 Water - 80 Ice - 3.2 Automotive Oil - 2.1 Figure 3. Capacitor Model MC34940 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 MC34940 offers 3 operating frequencies. In addition to the default frequency of 120 kHz, the MC34940 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 150 pF 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 an 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 10 nF and in practice it will have a response time of 2.5 ms. If faster response time is required a 1.0 nF capacitor can be used and it will have response times around 500 µs. Please note that reducing the LP_CAP capacitor value increases noise accordingly. Output Voltage vs Capacitance at 3 Discrete Frequencies 4 Voltage Output (Volts) 3.5 3 2.5 120 kHz 240 kHz 2 60 kHz 1.5 1 0.5 0 0 50 100 150 200 Capacitance (pF) Figure 4. Output Voltage vs. Capacitance at 3 Discrete Frequencies MC34940 Sensors Freescale Semiconductor 7 BASIC CONNECTIONS PIN DESCRIPTIONS Table 6. Pin Description DGND N/C Pin Number Pin Name Definition N/C E7 1 DGND Connected to the ground return SHIELDEN E6 2, 24 N/C These pins should be left open. C E5 B E4 3 SHIELDEN Used to enable the shield signal A E3 4,5,6 C, B, A Controls electrode or reference activity LEVEL E2 LPCAP E1 7 LEVEL This is the detected, amplified, and offset representation of the signal voltage on the selected electrode 8 LPCAP A capacitor on this pin forms a low pass filter with the internal series resistance from the detector to this pin 9 ROSC A resistor from this pin to circuit ground determines the operating frequency of the oscillator 10 VDDCAP A 47 µF capacitor is connected to this pin to filter the internal analog regulated supply 11 VPWR 12 VCCCAP A 47 µF capacitor is connected to this pin to filter the internal digital regulated supply 13 AGND Connected to the ground return of the analog circuitry 14 SHIELD 15 GND Main IC ground 16 TEST Connect to circuit ground 17-23 E1–E7 ROSC TEST VDDCAP GND VPWR SHIELD VCCCAP AGND Figure 5. Pin Descriptions Table 5. Electrode Selection Terminal/SIGNAL C B A No electrodes selected 0 0 0 E1 0 0 1 E2 0 1 0 E3 0 1 1 E4 1 0 0 E5 1 0 1 E6 1 1 0 E7 1 1 1 12 V power applied to this pin will be converted to the internal regulated voltages needed to operate the part Connects to cable shields to cancel cable capacitance. Electrode pins MC34940 47 µF 47 µF MCU VCCCAP ROSC 39k VDDCAP LPCAP 10 nF LEVEL Analog In 3 A, B, C Electrode Select Shield Enable E1 SHIELDEN Field Electrodes (E1 through E7) +12 V VPWR TEST AGND GND E7 SHIELD Figure 6. Simplified Application Diagram MC34940 8 Sensors Freescale Semiconductor PACKAGE DIMENSIONS PAGE 1 OF 2 EG SUFFIX CASE 751E-04 ISSUE F MC34940 Sensors Freescale Semiconductor 9 PACKAGE DIMENSIONS PAGE 2 OF 2 PAGE 2 OF 2 EG SUFFIX CASE 751E-04 ISSUE F MC34940 10 Sensors Freescale Semiconductor MC34940 Sensors Freescale Semiconductor 11 How to Reach Us: Home Page: www.freescale.com Web Support: http://www.freescale.com/support RoHS-compliant and/or Pb-free versions of Freescale products have the functionality and electrical characteristics of their non-RoHS-compliant and/or non-Pb-free counterparts. For further information, see http://www.freescale.com or contact your Freescale sales representative. For information on Freescale’s Environmental Products program, go to http:// www.freescale.com/epp. USA/Europe or Locations Not Listed: Freescale Semiconductor, Inc. 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