Converter IC for Capacitive Signals
FEATURES
•
Wide Supply Voltage Range: 6...35V
•
Wide Operating Temperature Range:
–40°C...+85°C
•
High Detection Sensitivity of Relative
Capacitive Changes: 5% – 100%
•
Detection Frequency up to 2kHz
•
Adjustable Voltage Range:
0...5/10V, other
•
Reference Voltage Source: 5V
•
Protection against Reverse Polarity
•
Output Current Limitation
•
Adjustable with only two Resistors
CAV414
GENERAL DESCRIPTION
The CAV414 is an universal multipurpose in-
terface for capacitive sensors and contains the
complete signal processing unit on chip. The
CAV414 detects the relative capacitive change
of a measuring capacity to a fixed reference
capacity. The IC is optimised for capacities in
the wide range of 10pF to 2nF with possible
changes of capacity of 5% to 100% of the ref-
erence capacity.
The voltage output is formed by a high accu-
racy instrumentation amplifier in combination
with an operational amplifier.
With only a few external components, the
CAV414 is suitable for a great variety of ap-
plications including a zero compensation.
APPLICATIONS
•
•
•
•
•
Industrial Process Control
Distance Measurement
Pressure Measurement
Humidity Measurement
Level Control
DELIVERY
•
DIL16 packages (samples)
•
SO16(n) packages
•
Dice on 5“ blue foil
BLOCK DIAGRAM
COSC
12
Reference
Oscillator
CAV414
IA
OP
VCC
9
CX1
16
Integrator 1
Integrator 2
Signal Conditioning
VOUT
8
7
10
CX2
14
GAIN
GND
Voltage/Current
Reference
15
13
4
5
6
2
3
1
11
VREF
CL1
Figure 1
CL2
RL LPOUT VM
RCX1 RCX2 RCOSC
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone: +49 (0)6131/91 073 – 0
Fax:
+49 (0)6131/91 073 – 30
E–Mail: info@analogmicro.de
January 2001
1/6
Rev. 2.1
Converter IC for Capacitive Signals
ELECTRICAL SPECIFICATIONS
T
amb
= 25°C,
V
CC
= 24V,
I
REF
= 1mA (unless otherwise noted)
Parameter
Supply
Supply Voltage
Quiescent Current
Temperature Specifications
Operating
Storage
Junction
Thermal Resistance
T
amb
T
st
T
j
Θ
ja
Θ
ja
Reference Oscillator
Oscillator Capacitor Range
Oscillator Frequency Range
Oscillator Current
Capacitive Integrator 1 and 2
Capacitor Range 1
Capacitive Integrator Current 1
Capacitor Detection Sensitivity
Capacitor Range 2
Capacitive Integrator Current 2
Detection Frequency
Lowpass
Adjustable Gain
Output Voltage
Corner Frequency 1
Corner Frequency 2
Resistive Load at PIN
LPOUT
Capacitive Load at PIN
LPOUT
Temperature Coefficient
V
DIFF
(together
with Input Stages)
Internal Resistor 1 and 2
Temperature Coefficient
R
01,02
Power Supply Rejection Ratio
(together with Input Stages)
Voltage Reference
V
REF
Voltage
Current
V
REF
vs. Temperature
Line Regulation
V
REF
I
REF
dV
REF
/dT
dV
REF
/dV
dV
REF
/ dV
Load Regulation
dV
REF
/dI
dV
REF
/dI
Load Capacitance
C
REF
I
REF
≈
4mA
1.9
T
amb
= –40...+85°C
Vcc
= 6V...35V
Vcc
= 6V...35V,
I
REF
≈
4mA
4.75
0
±90
30
60
0.05
0.06
2.2
5
G
LP
V
LPOUT
f
C1
f
C2
R
LOAD
C
LOAD
dV
DIFF
/dT
R
01
, R
02
dR
01,02
/dT
PSRR
T
amb
= –40 ... 85°C
I
OUT
≤
1mA
80
V
DIFF
=
V
LPOUT
-
V
M
,
T
amb
= –40 ... 85°C
±100
20
1.9
90
R
01
= 20kΩ,
C
L1
=1nF
R
02
= 20kΩ,
C
L2
=1nF
200
1
V
M
–0.4
C
X1
I
X1
∆
C
X
C
X2
I
X2
f
DET
R
CX1
= 400kΩ
∆
C
X
= (C
X2
−
C
X1
)/C
X1
C
X2
=
C
X1
⋅
(1 +
∆
C
X
)
R
CX2
= 400kΩ
C
L1
=
C
L2
=1nF
10
4.75
5
10.5
4.75
5
5
C
OSC
f
OSC
I
OSC
R
OSC
= 200kΩ
C
OSC
= 1.6
⋅
C
X1
14
1
9.5
10
DIL16 plastic package
SO16 (n) plastic package
70
140
–40
–55
V
CC
I
CC
T
amb
= –40 ... 85°C,
I
REF
= 0mA
6
1.55
Symbol
Conditions
Min.
Typ.
CAV414
Max.
Unit
35
2.7
V
mA
85
125
150
°C
°C
°C
°C/W
°C/W
1800
130
10.75
pF
kHz
µA
1000
5.38
100
2000
5.38
2
pF
µA
%
pF
µA
kHz
10
V
M
+0.4
10
10
V
kHz
kHz
kΩ
50
pF
ppm/°C
kΩ
10
-3
/°C
dB
5.25
9
±140
80
150
0.10
0.15
5.0
V
mA
ppm/°C
ppm/V
ppm/V
%/mA
%/mA
µF
analog microelectronics
January 2001
2/6
Converter IC for Capacitive Signals
Parameter
Voltage Reference
V
M
Voltage
V
M
vs. Temperature
Current
V
M
dV
M
/dT
I
VM
I
VM
Load Capacitance
Instrumentation Amplifier Input Stage
Internal Gain
Differential Range
Common Mode Input Range
G
IA
V
IN
CMIR
CMIR
Common Mode Rejection Ratio
Power Supply Rejection Ratio
Offset Voltage
V
OS
vs. Temperature
Output Stage
Adjustable Gain
Input Range
G
OP
IR
IR
Power Supply Rejection Ratio
Offset Voltage
V
OS
vs. Temperature
Input Bias Current
I
B
vs. Temperature
Output Voltage Range
PSRR
V
OS
dV
OS
/dT
I
B
dI
B
/dT
V
OUT
V
OUT
Output Current Limitation
Output Current
Load Resistance
Load Capacitance
Protection Functions
Protection Against Reverse Polarity
Ground
vs.
V
CC
vs.
V
OUT
I
LIM
I
OUT
R
L
C
L
V
CC
< 19V
V
CC
≥
19V
V
CC
≥
10V
0
0
5
0
2
7
V
CC
< 11V
V
CC
≥
11V
I
OUT
≤
1mA
1
0
0
80
90
±0.5
±3
10
7
CMRR
PSRR
V
OS
dV
OS
/dT
I
OUT
≤
1mA
V
CC
< 9V,
I
CV
< 2mA
V
CC
≥
9V,
I
CV
< 2mA
4.9
0
1.5
1.5
80
80
90
90
±1.5
±5
5
C
VM
T
amb
= –40...+85°C
Source
Sink
80
100
1.90
2
±90
Symbol
Conditions
Min.
Typ.
CAV414
Max.
Unit
2.15
V
ppm/°C
µA
µA
nF
5
-5
120
5.1
400
V
CC
- 3
6.0
mV
V
V
dB
dB
±6
mV
µV/°C
V
CC
- 5
6
V
V
dB
±2
±7
25
20
V
CC
- 5
14
10
I
LIM
500
mV
µV/°C
nA
pA/°C
V
V
mA
mA
kΩ
nF
35
V
Note:
1) The oscillator capacity has to be chosen in the following way:
C
OSC
= 1.6
⋅
C
X1
2) The capacitor range of
C
X1
and
C
X2
can be extended whereby the system performance is reduced and the electrical
limits are exceeded.
3) Currents flowing into the IC, are negative.
analog microelectronics
January 2001
3/6
Converter IC for Capacitive Signals
BOUNDARY CONDITIONS
Parameter
Current Definition of Ref. Oscillator
Current Adjustment of Cap. Integrator 1
Current Adjustment of Cap. Integrator 2
Lowpass Stage Resistor Sum
Output Stage Resistor Sum
Reference Voltage 5V
Reference Voltage 2V (only for internal use)
Lowpass Capacitance 1
Lowpass Capacitance 2
Oscillator Capacitance
Symbol
R
COSC
R
CX1
R
CX2
R
L1
+ R
L2
R
1
+ R
2
C
REF
C
VM
C
L1
C
L2
C
OSC
Min.
190
350
350
90
90
1.9
80
100⋅C
X1
100⋅C
X1
C
OSC
=1.55⋅C
X1
2.2
100
200⋅C
X1
200⋅C
X1
C
OSC
=1.60⋅C
X1
Typ.
200
400
400
CAV414
Max.
210
450
450
200
200
5
120
Unit
kΩ
kΩ
kΩ
kΩ
kΩ
µF
nF
C
OSC
=1.65⋅C
X1
Note:
The system performance over temperature forces that the resistors
R
CX1
,
R
CX2
and
R
OSC
have the same temperature
coefficient and a very close placement of them in the circuit. The capacities
C
X1
,
C
X2
and
C
OSC
are also forced to
have the same temperature coefficient and a very close placement of them in the circuit.
FUNCTIONAL DIAGRAM
12
C
OSC
16
C
X1
14
C
X2
Reference
Oscillator
V
CX1
V
CX2
CAV414
V
LPOUT
V
M
9
8
R
1
7
R
2
10
VCC
OUT
IA
V
DIFF
Integrator 1
Integrator 2
OP
Signal Conditioning
V
CX,DIFF
GND
Voltage/Current
Reference
11
C
REF
R
01
15
C
L1
R
02
13
C
L2
4
R
L1
R
L2
5
6
C
VM
2
R
CX1
3
R
CX2
1
R
OSC
Figure 2
analog microelectronics
January 2001
4/6
Converter IC for Capacitive Signals
FUNCTIONAL DESCRIPTION
CAV414
A reference oscillator with a frequency adjusted by the capacity
C
OSC
drives two symmetrically built
integrators synchronously to its clock and its phase. The capacitors
C
X1
and
C
X2
determine the am-
plitude of the two driven integrators. The difference of the integrator amplitudes gives the relative
change of the capacities
C
X1
and
C
X2
to each other with high common mode rejection and high
resolution. The difference signal is conditioned by a lowpass filter. The corner frequency and gain
of it can be adjusted with a few external components. The output of the lowpass filter is connected
to an instrumentation amplifier and an output stage. These two stages transform the signal into an
adjustable voltage.
Adjustment:
The zero-adjustment is made by the resistors
R
CX1
or
R
CX2
for the case that the varying capacitance
C
X2
has nearly the same (and its smallest) value as the fixed capacitance
C
X1
(reference capacitance).
Therefore one of this resistors is varied until the differential voltage
V
DIFF
=
V
LPOUT
−
V
M
is zero:
V
DIFF
=
0
Application Example:
The following values are given:
•
fixed capacitance
C
X1
:
•
varying capacitance
C
X2
:
Calculation:
With the equations given in the boundary conditions, the following values for the devices can be
calculated:
•
C
OSC
:
•
C
L1
:
•
C
L2
:
80pF
10nF
10nF
50pF
50 ... 100pF
If the signal
V
DIFF
is amplified, it has to fulfil the unequation:
V
DIFF
≤
400mV
Detailed calculations are shown in a separately available
Application Note.
analog microelectronics
January 2001
5/6
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