MC34940R2 [FREESCALE]
Electric Field Imaging Device; 电场成像器件
| 型号： | MC34940R2 |
| 厂家： | 
Freescale |
| 描述： | Electric Field Imaging Device |
| 文件： | 总9页 (文件大小：294K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Document order number: MC34940
Rev 2.0, 2/2006
Freescale Semiconductor
Technical Data
Electric Field Imaging Device
The 34940 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 34940 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 34940 also contains support
circuits for a microcontroller unit (MCU) to allow the construction of a two-chip
E-field system.
34940
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
•
•
•
•
•
•
•
•
•
•
•
•
•
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
24 LEAD (PB-FREE)
SOICW
98ASB42344B
DGND
N/C
N/C
E7
SHIELDEN
C
E6
Garage Door Safety Sensing
PC Peripherals
E5
B
E4
Patient Monitoring
A
E3
LEVEL
LPCAP
ROSC
VDDCAP
VPWR
VCCCAP
E2
Point of Sale Terminals
E1
Size Detection
TEST
GND
SHIELD
AGND
Liquid Level Sensing
ORDERING INFORMATION
Temperature
Device Name
Drawing
Package
Figure 1. Pin Connections
Range
MC34940EG/R2
0 to 90°C
98ASB42564B
SOICW-24
© Freescale Semiconductor, Inc., 2006. All rights reserved.
3
A,B,C
E1-E7
CONTROL
LOGIC
2.8 kΩ
2.8 kΩ
ROSC
OSC
MUX
OUT
22 kΩ (Nominal)
SHIELDEN
SHIELD
150 Ω
MUX
IN
700Ω
RECT
700Ω
LPCAP
LEVEL
LPF
VCCCAP
VDDCAP
GAIN AND
OFFSET
VCC
REG
VPWR
VDD
REG
AGND
GND
Figure 2. Simplified Functional Block Diagram
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 V Voltage
V
40
V
V
PWR
PWRPK
Double Battery
V
DBLBAT
1 Minute Maximum T = 30°C
A
26.5
ESD Voltage
V
V
ESD
Human Body Model (CZAP = 100 pF, RZAP = 1500 W)
Machine Model (CZAP = 200 pF, RZAP = 0 W)
±2000
±200
Charge Device Model (CDM), Robotic (CZAP = 4.0pF)
±1200
Thermal Ratings
Storage Temperature
T
-55 to 150
-0 to 90
°C
°C
STG
Operating Ambient Temperature
Operating Junction Temperature
T
A
T
-0 to 150
°C
J
Thermal Resistance
Junction-to-Ambient (1)
Junction-to-Case (2)
Junction-to-Board (3)
°C/W
R
R
R
41
0.2
3.0
θJA
θJC
θJB
Soldering Temperature(4)
T
260
°C
SOLDER
MC34940
Sensors
2
Freescale Semiconductor
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
Unit
SUPPLY (VPWR
)
Supply Voltage
VPWR
V
9.0
6.0
12
18
IDD (VPWR = 14V)
I
mA
DD
(Quiescent supply current measured over temperature. Assumes
that no external devices connected to internal voltage regulators)
7.0
8.0
ELECTRODE SIGNALS (E1–E7)
Total Variance Between Electrode Measurements (5)
ELV
%
dB
V
VAR
All C
= 15 pF
LOAD
–
–
–
3.0
–
Electrode Maximum Harmonic Level Below Fundamental (5)
5.0 pF ≤ C ≤ 150 pF
EL
HARM
LOAD
-20
Electrode Transmit Output Range
5.0 pF ≤ C ≤ 150 pF
EL
TXV
LOAD
1.0
0
–
–
8.0
9.0
Receive Input Voltage Range
Grounding Switch on Voltage(6)
RX
V
V
V
SW
VON
I
= 1.0 mA
SW
–
–
5.0
LOGIC I/O (C, B, A)
CMOS Logic Input Low Threshold
Logic Input High Threshold
Voltage Hysteresis
V
0.3
–
–
–
–
0.7
–
V
V
V
THL
THH
HYS
CC
CC
CC
V
V
–
0.06
Input Current
I
µA
IN
V
V
= V
CC
IN
IN
10
–
–
50
= 0 V
-5.0
5.0
SIGNAL DETECTOR (LPCAP)
Detector Output Resistance
LPCAP to LEVEL Gain
DET
–
50
4.0
-3.0
–
kΩ
RO
A
3.6
-3.3
4.4
-2.7
A
V
REC
LPCAP to LEVEL Offset
V
V
RECOFF
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
5. Verified by design and characterization. Not tested in production.
6. Current into grounded terminal under test = 1.0 mA.
MC34940
Sensors
Freescale Semiconductor
3
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 (ROSC)
OSC Frequency Stability
f
–
–
10
%
STAB
OSC Center Frequency
ROSC = 39 kΩ
f
kHz
OSC
–
–
–
120
240
60
–
–
–
ROSC = 20 kΩ
ROSC = 82 kΩ
Harmonic Content
OSCH
dB
ARM
2nd through 4th Harmonic Level
5th and Higher
–
–
–
–
-20
-60
SHIELD DRIVER (SHIELD)
Shield Driver Maximum Harmonic level below Fundamental
SD
dB
HARM
10 pF ≤ C
≤ 500 pF
LOAD
–
–
-20
4.5
–
–
Shield Driver Gain Bandwidth Product
Measured at 120 kHz
SD
MHz
GBW
MC34940
Sensors
4
Freescale Semiconductor
PRINCIPLE OF OPERATION
The 34940 generates a low radio frequency sine wave with
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.
nominal 5.0 V peak-to-peak amplitude. The frequency is set
by and 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 and
external capacitor, is multiplied and offset to increase
sensitivity. All electrode outputs are grounded internally by
the device when not selected.
While exploring applications using the E-Field chip, it is
always useful to approach the problem using the capacitor
model.
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
Voltage Level Proportional to 1/C (voltage divider)
Low Pass Filter
Detector
Load Resistor
(22 K ohms)
Stray Variable
Capacitance
Electrodes
Detected Signal
Level Decreases
with Increasing
Capacitance
Object
Sine Generator
(120 KHz)
Capacitance
increases as
electrodes move
closer together
Virtual Ground
Capacitor Model
Figure 3. Conceptual Block Diagram
CAPACITOR MODEL
The capacitance measured by the E-Field IC is:
Proportional to the area of the electrode
Table 4 Dielectric Constants of Various Materials
•
•
Dielectric Material
Acrylic
Thickness (mil)
k
Proportional to the dielectric constant of the material
between the electrodes
84.5
2.4-4.5
7.5
Glass
74.5
•
Inversely proportional to the distance between the objects
Nylon Plastic
Polyester Film
Flexible Vinyl Film
Air
68
10
9
-
3.0-5.0
3.2
2.8-4.5
1
kε0 A
d
d
k
C
C =
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 4. Capacitor Model
MC34940
Sensors
Freescale Semiconductor
5
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.
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 5. 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 2.5ms. If faster response time is required a
1nF capacitor can be used and it will have response times
around 500uS. Please note that reducing the LP_CAP
capacitor value increases noise accordingly.
TUNABLE FREQUENCY
The 34940 offers 3 operating frequencies. In addition to
the default frequency of 120 kHz, the 34940 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
Output Voltage vs Capacitance at 3 Discrete Frequencies
4
3.5
3
2.5
2
120 kHz
240 kHz
60 kHz
1.5
1
0.5
0
0
20
40
60
80
100
120
140
160
Capacitance (pF)
Figure 5 Output Voltage vs. Capacitance at 3 Discrete Frequencies
MC34940
Sensors
6
Freescale Semiconductor
BASIC CONNECTIONS
Table 6. Pin Description
Pin Descriptions
Pin
Number
Pin Name
Definition
DGND
N/C
E7
N/C
SHIELDEN
C
Connected to the ground return
These pins should be left open.
Used to enable the shield signal
Controls electrode or reference activity
1
2, 24
3
DGND
N/C
E6
E5
B
SHIELDEN
C, B, A
LEVEL
E4
A
E3
4,5,6
7
LEVEL
LPCAP
ROSC
VDDCAP
VPWR
VCCCAP
E2
This is the detected, amplified, and
offset representation of the signal
voltage on the selected electrode
E1
TEST
GND
SHIELD
AGND
A capacitor on this pin forms a low pass
filter with the internal series resistance
from the detector to this pin
8
LPCAP
ROSC
Figure 6 Pin Descriptions
A resistor from this pin to circuit ground
determines the operating frequency of
the oscillator
9
Table 5. Electrode Selection
A 47µF capacitor is connected to this
pin to filter the internal analog regulated
supply
10
11
12
VDDCAP
VPWR
Terminal/SIGNAL
C
B
A
No electrodes selected
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
12 V power applied to this pin will be
converted to the internal regulated
voltages needed to operate the part
E1
E2
E3
E4
E5
E6
E7
A 47µF capacitor is connected to this
pin to filter the internal digital regulated
supply
VCCCAP
Connected to the ground return of the
analog circuitry
13
14
AGND
Connects to cable shields to cancel
cable capacitance.
SHIELD
Main IC ground
15
16
GND
TEST
E1–E7
Connect to circuit ground
Electrode pins
17-23
MC34940
ROSC
VCCCAP
VDDCAP
47uF
39k
47uF
LPCAP
MCU
10nF
LEVEL
A, B, C
Analog In
3
Electrode Select
Shield Enable
E1
SHIELDEN
Field Electrodes
(E1 through E7)
+12V
VPWR
TEST
AGND
GND
E7
SHIELD
Figure 7 Simplified Application Diagram
MC34940
Sensors
Freescale Semiconductor
7
PACKAGING DIMENSIONS
EG SUFFIX
24-TERMINAL SOICW
98ASB42344B
ISSUE F
MC34940
Sensors
8
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MC34940
Rev 2.0
2/2006
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