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semrconductar
freescale‘"
Document Number: MC33941
Rev. 4
Freescale Semiconductor
Technical Data
© Freescale Semiconductor, Inc., 2008. All rights reserved.
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 -40° to 110°C
• Pb-Free and RoHS compliant
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 Temperature
Range Drawing Package
MC33941EG/R2 -40° to 110°C 98ASB42564B SOICW-24
MC33941
ELECTRONIC FIELD
IMAGING DEVICE
EG SUFFIX (Pb-FREE)
24-TERMINAL SOICW
CASE 751E-05
N/C
E7
E6
E5
E4
E3
E2
E1
TEST
GND
SHIELD
AGND
DGND
N/C
SHIELDEN
C
B
A
LEVEL
LPCAP
ROSC
VDDCAP
VPWR
VCCCAP
Pin Connections
MC33941
Sensors
2Freescale Semiconductor
Figure 1 Simplified Functional Block Diagram
OSC
700Ω
700Ω
LEVEL
LPCAP
VDDCAP
VCCCAP
VPWR
AGND
GND
ROSC
SHIELDEN
SHIELD
E1-E7
A,B,C
150 Ω
RECT
LPF
GAIN AND
OFFSET
MUX
IN
CONTROL
LOGIC
MUX
OUT
3
22 kΩ (Nominal)
2.8 kΩ
2.8 kΩ
VCC
REG
VDD
REG
MC33941
Sensors
Freescale Semiconductor 3
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
ELECTRICAL RATINGS
Peak VPWR Voltage VPWRPK 40 V
Double Battery
1 Minute Maximum TA = 30°C
VDBLBAT
26.5
V
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)
VESD ±2000
±200
±1200
V
THERMAL RATINGS
Storage Temperature TSTG -55 to 150 °C
Operating Ambient Temperature TA-40 to 110 °C
Operating Junction Temperature TJ -40 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
°C/W
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 G38-
87 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.
MC33941
Sensors
4Freescale Semiconductor
Table 2. Static Electrical Characteristics
Characteristics noted under conditions 5.5 V ≤VSUP ≤18 V, -40°C≤TA ≤110°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
SUPPLY (VPWR)
Supply Voltage VPWR 9.0 12 18 V
IDD (VPWR = 14V)
(Quiescent supply current measured over temperature. Assumes
that no external devices connected to internal voltage regulators)
IDD
6.0 7.0 8.0
mA
VOLTAGE REGULATOR
5V Regulator Voltage
7.0 V ≤ VPWR ≤ 18 V, 1.0 mA ≤ IL ≤ 75 mA, CFILT = 47 μF
VCCCAP
4.75 55.25
V
ELECTRODE SIGNALS (E1–E7)
Total Variance Between Electrode Measurements (5)
All CLOAD = 15 pF
ELVVAR
– – 3.0
%
Electrode Maximum Harmonic Level Below Fundamental (5)
5.0 pF ≤ CLOAD ≤ 150 pF
ELHARM
–-20
–
dB
Electrode Transmit Output Range
5.0 pF ≤ CLOAD ≤ 150 pF
ELTXV
1.0 – 8.0
V
Receive Input Voltage Range RXV 0 – 9.0 V
Grounding Switch on Voltage(6)
ISW = 1.0 mA
SWVON
– – 5.0
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
Input Current
VIN = VCC
VIN = 0 V
IIN
10
-5.0
–
–
50
5.0
μA
SIGNAL DETECTOR (LPCAP)
Detector Output Resistance 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
Notes
5. Verified by design and characterization. Not tested in production.
6. Current into grounded terminal under test = 1.0 mA.
MC33941
Sensors
Freescale Semiconductor 5
Table 3. Dynamic Electrical Characteristics (7)
Characteristics noted under conditions 5.5 V ≤VSUP ≤18 V, -40°C≤TA ≤110°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 (ROSC)
OSC Frequency Stability fSTAB – – 10 %
OSC Center Frequency
ROSC = 39 kΩ
ROSC = 20 kΩ
ROSC = 82 kΩ
fOSC –
–
–
120
240
60
–
–
–
kHz
Harmonic Content
2nd through 4th Harmonic Level
5th and Higher
OSCHARM
–
–
–
–
-20
-60
dB
SHIELD DRIVER (SHIELD)
Shield Driver Maximum Harmonic level below Fundamental
10 pF ≤ CLOAD ≤ 500 pF
SDHARM
– -20 –
dB
Shield Driver Gain Bandwidth Product
Measured at 120 kHz
SDGBW
–4.5 –
MHz
Notes
7. All parameters are guaranteed by design.
Load Reslsto
(22 K ohms) / Detector
*i
Stray Variable ,,
Ca acitance“
P Electrodes Detected Signal
Level Decreases
Object with lncreaslng
Sine Generator Capacflance
(120 KHZ) Capacitance
increases as
electrodes move
Virtual Ground 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 ol the materlal
between the electrodes
- Inversely proportional to the distance between the objects
Figure 3. Capacitor Model
M033941
MC33941
Sensors
6Freescale Semiconductor
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.
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
Figure 3. Capacitor Model
Detector Low Pass Filter
Voltage Level Proportional to 1/C (voltage divider)
Drive level ~ 5 v p-p
Load Resistor
(22 K ohms)
Sine Generator
(120 KHz)
Detected Signal
Level Decreases
with Increasing
Capacitance
Electrodes
Capacitance
increases as
electrodes move
closer together
Capacitor Model
Virtual Ground
Stray Variable
Capacitance
Object
Detector Low Pass Filter
Voltage Level Proportional to 1/C (voltage divider)
Drive level ~ 5 v p-p
Load Resistor
(22 K ohms)
Sine Generator
(120 KHz)
Detected Signal
Level Decreases
with Increasing
Capacitance
Electrodes
Capacitance
increases as
electrodes move
closer together
Capacitor Model
Virtual Ground
Stray Variable
Capacitance
Object
d
Ak
C0
ε
=
Ckd
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 92.8-4.5
Air - 1
Water -80
Ice -3.2
Automotive Oil -2.1
MC33941
Sensors
Freescale Semiconductor 7
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
<200μS. Please note that reducing the LP_CAP capacitor
value increases noise accordingly.
Figure 4 . Output Voltage vs. Capacitance at 3 Discrete Frequencies
Output Voltage vs Capacitance at 3 Discrete Frequencies
0
0.5
1
1.5
2
2.5
3
3.5
4
0 20 40 60 80 100 120 140 160
Capacitance (pF)
Voltage Output (Volts)
120 kHz
240 kHz
60 kHz
243::
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EEEWIIII
MC33941
Sensors
8Freescale Semiconductor
BASIC CONNECTIONS
PIN DESCRIPTIONS
Figure 5. Pin Descriptions
Figure 6 . Simplified Application Diagram
Table 5. Electrode Selection
Terminal/SIGNAL C B A
No electrodes selected 0 0 0
E1 0 0 1
E2 01 0
E3 0 1 1
E4 1 0 0
E5 1 0 1
E6 1 1 0
E7 1 1 1
N/C
E7
E6
E5
E4
E3
E2
E1
TEST
GND
SHIELD
AGND
DGND
N/C
SHIELDEN
C
B
A
LEVEL
LPCAP
ROSC
VDDCAP
VPWR
VCCCAP
Table 6. Pin Description
Pin
Number Pin Name Definition
1DGND Connected to the ground return
2, 24 N/C These pins should be left open.
3SHIELDEN Used to enable the shield signal
4,5,6 C, B, A Controls electrode or reference activity
7LEVEL This is the detected, amplified, and
offset representation of the signal
voltage on the selected electrode
8LPCAP A capacitor on this pin forms a low pass
filter with the internal series resistance
from the detector to this pin
9ROSC A resistor from this pin to circuit ground
determines the operating frequency of
the oscillator
10 VDDCAP A 47μF capacitor is connected to this
pin to filter the internal analog regulated
supply
11 VPWR 12 V power applied to this pin will be
converted to the internal regulated
voltages needed to operate the part
12 VCCCAP A 47μF capacitor is connected to this
pin and VCCCAP provides a regulated
5.0 V to power external circuits 75 mA
Max
13 AGND Connected to the ground return of the
analog circuitry
14 SHIELD Connects to cable shields to cancel
cable capacitance.
15 GND Main IC ground
16 TEST Connect to circuit ground
17-23 E1–E7 Electrode pins
MC33941
Field Electrodes
(E1 through E7)
MCU
SHIELDEN
AGND
TEST
ROSC
GND
VDDCAP
E1
E7
SHIELD
VPWR
Analog In
Electrode Select
Shield Enable
LPCAP
LEVEL
A, B, C
VCCCAP
3
+12V
39k
10nF
47uF
47uF
Power
+5V
12X mas
TDD5
PW T
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TTTLE: DOCUMENT NO: 95A5942344E REV: c
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7.5 X 15.4 CASE NUMBER 751E705 05 DED 2007
CASEiouTLTNE STANDARD: JEDEC M57013 AD
PACKAGE DIMENSIONS
CASE 751E-05
ISSUE G
24-LEAD SOIC
PAGE 1 OF 2
Sensors
Freescale Semiconductor 9
MC33941
NDTES:
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2, DTMENSTDMS ARE TM M‘LL‘METERSL
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‘HTLE: 24LD SO‘C W/B, 127 P‘TCH DOCUMENT NO:98ASB42344B REV: G
7‘5 X 15.4 CASE NUMBER: 751E705 05 DEC 2007
CASEiOUTUNE
STANDARD: JEDEC MSiOTK AD
PACKAGE DIMENSIONS
CASE 751E-05
ISSUE G
24-LEAD SOIC
PAGE 2 OF 2
MC33941
Sensors
10 Freescale Semiconductor
o
'0
:9 freescale‘"
semrconductar
MC33941
Rev. 4
09/2008
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