MC34940EGR2 Freescale Semiconductor, MC34940EGR2 Datasheet - Page 6

• Manufacturer Part Number: MC34940EGR2
• Description: IC IMAGING DEVICE ELEC 24-SOICW
• Manufacturer: Freescale Semiconductor
• Type: Image Sensorr

Specifications of MC34940EGR2

• Input Type: Logic
• Output Type: Voltage
• Current - Supply: 8mA
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)
• Maximum Operating Temperature: + 90 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: 0 C
• For Use With: DEMO1985MC34940E - KIT DEMO FOR MC34940E FAMILY
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Interface: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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.
electrode are affected by objects in proximity. A “capacitor” is
CAPACITOR MODEL
•
•
•
6
MC34940
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)
The MC34940 generates a low radio frequency sine wave
The amplitude and phase of the sinusoidal wave at the
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
C
=
Drive level ~ 5 V p-p
k
ε
Sine Generator
d
0
Figure 3. Capacitor Model
A
(120 kHz)
Load Resistor
(22 kΩ)
Stray Variable
Capacitance
C
k
Figure 2. Conceptual Block Diagram
Virtual Ground
PRINCIPLE OF OPERATION
d
Voltage Level Proportional to 1/C (voltage divider)
Capacitance
increases as
electrodes move
closer together
Electrodes
Object
Detector
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.
always useful to approach the problem using the capacitor
model.
While exploring applications using the E-Field chip, it is
Capacitor Model
Table 4. Dielectric Constants of Various Materials
Acrylic
Glass
Nylon Plastic
Polyester Film
Flexible Vinyl Film
Air
Water
Ice
Automotive Oil
Dielectric Material
Detected Signal
Level Decreases
with Increasing
Capacitance
Low Pass Filter
Thickness (mil)
84.5
74.5
68
10
9
-
-
-
-
Freescale Semiconductor
2.4-4.5
3.0-5.0
2.8-4.5
7.5
3.2
1.0
3.2
2.1
80
k
Sensors