FREESCALE MC33941_08

Document Number: MC33941
Rev. 4
Freescale Semiconductor
Technical Data
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.
MC33941
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
+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
EG SUFFIX (Pb-FREE)
24-TERMINAL SOICW
CASE 751E-05
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
DGND
E7
SHIELDEN
E6
C
E5
B
E4
A
E3
LEVEL
E2
LPCAP
E1
ROSC
VDDCAP
VPWR
VCCCAP
Pin Connections
ORDERING INFORMATION
Device Name
Temperature
Range
Drawing
Package
MC33941EG/R2
-40° to 110°C
98ASB42564B
SOICW-24
© Freescale Semiconductor, Inc., 2008. All rights reserved.
N/C
N/C
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
MC33941
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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
Peak VPWR Voltage
VPWRPK
40
V
Double Battery
VDBLBAT
ELECTRICAL RATINGS
1 Minute Maximum TA = 30°C
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)
V
26.5
VESD
V
±2000
±200
±1200
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
RθJA
RθJC
RθJB
41
0.2
3.0
Thermal Resistance
Junction-to-Ambient (1)
Junction-to-Case (2)
Junction-to-Board (3)
°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 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.
MC33941
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Freescale Semiconductor
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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
VPWR
9.0
12
18
V
6.0
7.0
8.0
SUPPLY (VPWR)
Supply Voltage
IDD (VPWR = 14V)
IDD
(Quiescent supply current measured over temperature. Assumes
that no external devices connected to internal voltage regulators)
mA
VOLTAGE REGULATOR
5V Regulator Voltage
VCCCAP
7.0 V ≤ VPWR ≤ 18 V, 1.0 mA ≤ IL ≤ 75 mA, CFILT = 47 μF
V
4.75
5
5.25
ELECTRODE SIGNALS (E1–E7)
Total Variance Between Electrode Measurements (5)
ELVVAR
All CLOAD = 15 pF
Electrode Maximum Harmonic Level Below Fundamental
(5)
Receive Input Voltage Range
Grounding Switch on
–
3.0
–
-20
–
1.0
–
8.0
0
–
9.0
–
–
5.0
dB
ELTXV
5.0 pF ≤ CLOAD ≤ 150 pF
Voltage(6)
–
ELHARM
5.0 pF ≤ CLOAD ≤ 150 pF
Electrode Transmit Output Range
%
RXV
V
SWVON
ISW = 1.0 mA
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
Input Current
μA
IIN
VIN = VCC
10
–
50
VIN = 0 V
-5.0
–
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
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.
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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 Frequency Stability
f STAB
–
–
10
%
OSC Center Frequency
ROSC = 39 kΩ
ROSC = 20 kΩ
ROSC = 82 kΩ
f OSC
–
–
–
120
240
60
–
–
–
2nd through 4th Harmonic Level
–
–
-20
5th and Higher
–
–
-60
OSC (ROSC)
Harmonic Content
kHz
OSCHARM
dB
SHIELD DRIVER (SHIELD)
Shield Driver Maximum Harmonic level below Fundamental
SDHARM
10 pF ≤ CLOAD ≤ 500 pF
Shield Driver Gain Bandwidth Product
Measured at 120 kHz
dB
–
-20
–
–
4.5
–
SDGBW
MHz
Notes
7. All parameters are guaranteed by design.
MC33941
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Freescale Semiconductor
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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
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 (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.
Voltage Level Proportional to 1/C (voltage divider)
Load Resistor
(22 K ohms)
Low Pass Filter
Detector
Stray Variable
Capacitance
Electrodes
Object
Sine Generator
(120 KHz)
Virtual Ground
Detected Signal
Level Decreases
with Increasing
Capacitance
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
•
•
kε A
C= 0
d
C
k
d
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
Water
-
80
Ice
-
3.2
Automotive Oil
-
2.1
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
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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.
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
20
40
60
80
100
120
140
160
Capacitance (pF)
Figure 4 . Output Voltage vs. Capacitance at 3 Discrete Frequencies
MC33941
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Freescale Semiconductor
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BASIC CONNECTIONS
PIN DESCRIPTIONS
Table 6. Pin Description
DGND
N/C
Pin
Number
Pin Name
1
DGND
Connected to the ground return
Definition
N/C
E7
SHIELDEN
E6
2, 24
N/C
These pins should be left open.
C
E5
3
SHIELDEN
Used to enable the shield signal
B
E4
A
E3
4,5,6
C, B, A
Controls electrode or reference activity
LEVEL
E2
7
LEVEL
LPCAP
E1
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 47μF capacitor is connected to this
pin to filter the internal analog regulated
supply
11
VPWR
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
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
+5V
MC33941
VCCCAP
ROSC
47uF
39k
VDDCAP
47uF
MCU
Power
LPCAP
10nF
LEVEL
Analog In
3
A, B, C
Electrode Select
Shield Enable
E1
SHIELDEN
Field Electrodes
(E1 through E7)
+12V
VPWR
TEST
AGND
GND
E7
SHIELD
Figure 6 . Simplified Application Diagram
MC33941
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PACKAGE DIMENSIONS
PAGE 1 OF 2
CASE 751E-05
ISSUE G
24-LEAD SOIC
MC33941
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PACKAGE DIMENSIONS
PAGE 2 OF 2
CASE 751E-05
ISSUE G
24-LEAD SOIC
MC33941
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Freescale Semiconductor
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MC33941
Rev. 4
09/2008
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