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Converter IC for Capacitive Signals
FEATURES
* Wide Supply Voltage Range: 6...35V * Wide Operating Temperature Range: -40C...+85C * 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 interface 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 reference capacity. The voltage output is formed by a high accuracy instrumentation amplifier in combination with an operational amplifier. With only a few external components, the CAV414 is suitable for a great variety of applications 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
Tamb = 25C, VCC = 24V, IREF = 1mA (unless otherwise noted)
Parameter Supply Supply Voltage Quiescent Current Temperature Specifications Operating Storage Junction Thermal Resistance Tamb Tst Tj ja 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 VDIFF (together with Input Stages) Internal Resistor 1 and 2 Temperature Coefficient R01,02 Power Supply Rejection Ratio (together with Input Stages) Voltage Reference VREF Voltage Current VREF vs. Temperature Line Regulation VREF IREF dVREF /dT dVREF /dV dVREF / dV Load Regulation dVREF /dI dVREF /dI Load Capacitance CREF IREF 4mA 1.9 Tamb = -40...+85C Vcc = 6V...35V Vcc = 6V...35V, IREF 4mA 4.75 0 90 30 60 0.05 0.06 2.2 5 GLP VLPOUT fC1 fC2 RLOAD CLOAD dVDIFF /dT R01, R02 dR01,02 /dT PSRR Tamb = -40 ... 85C IOUT 1mA 80 VDIFF = VLPOUT - VM , Tamb = -40 ... 85C 100 20 1.9 90 R01 = 20k, CL1 =1nF R02 = 20k, CL2 =1nF 200 1 VM -0.4 CX1 IX1 CX CX2 IX2 fDET RCX1 = 400k CX = (CX2 - CX1 )/CX1 CX2 = CX1 (1 + CX ) RCX2 = 400k CL1 = CL2 =1nF 10 4.75 5 10.5 4.75 5 5 COSC fOSC IOSC ROSC = 200k COSC = 1.6 CX1 14 1 9.5 10 DIL16 plastic package SO16 (n) plastic package 70 140 -40 -55 VCC ICC Tamb = -40 ... 85C, IREF = 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 A
1000 5.38 100 2000 5.38 2
pF A % pF A kHz
10 VM +0.4 10 10 V kHz kHz k 50 pF ppm/C k 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 F
analog microelectronics
January 2001 2/6
Converter IC for Capacitive Signals
Parameter Voltage Reference VM Voltage VM vs. Temperature Current VM dVM /dT IVM IVM Load Capacitance Instrumentation Amplifier Input Stage Internal Gain Differential Range Common Mode Input Range GIA VIN CMIR CMIR Common Mode Rejection Ratio Power Supply Rejection Ratio Offset Voltage VOS vs. Temperature Output Stage Adjustable Gain Input Range GOP IR IR Power Supply Rejection Ratio Offset Voltage VOS vs. Temperature Input Bias Current IB vs. Temperature Output Voltage Range PSRR VOS dVOS /dT IB dIB /dT VOUT VOUT Output Current Limitation Output Current Load Resistance Load Capacitance Protection Functions Protection Against Reverse Polarity Ground vs. VCC vs. VOUT ILIM IOUT RL CL VCC < 19V VCC 19V VCC 10V 0 0 5 0 2 7 VCC < 11V VCC 11V IOUT 1mA 1 0 0 80 90 0.5 3 10 7 CMRR PSRR VOS dVOS /dT IOUT 1mA VCC < 9V, ICV < 2mA VCC 9V, ICV < 2mA 4.9 0 1.5 1.5 80 80 90 90 1.5 5 5 CVM Tamb = -40...+85C Source Sink 80 100 1.90 2 90 Symbol Conditions Min. Typ.
CAV414
Max. Unit
2.15
V ppm/C A A nF
5 -5 120
5.1 400 VCC - 3 6.0 mV V V dB dB 6 mV V/C
VCC - 5 6
V V dB
2 7 25 20 VCC - 5 14 10 ILIM 500
mV V/C nA pA/C V V mA mA k nF
35
V
Note: 1) The oscillator capacity has to be chosen in the following way: COSC = 1.6 CX1 2) The capacitor range of CX1 and CX2 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 RCOSC RCX1 RCX2 RL1 + RL2 R1 + R2 CREF CVM CL1 CL2 COSC Min. 190 350 350 90 90 1.9 80 100CX1 100CX1 COSC =1.55CX1 2.2 100 200CX1 200CX1 COSC =1.60CX1 Typ. 200 400 400
CAV414
Max. 210 450 450 200 200 5 120
Unit k k k k k F nF
COSC =1.65CX1
Note: The system performance over temperature forces that the resistors RCX1, RCX2 and ROSC have the same temperature coefficient and a very close placement of them in the circuit. The capacities CX1, CX2 and COSC are also forced to have the same temperature coefficient and a very close placement of them in the circuit.
FUNCTIONAL DIAGRAM
12 COSC 16 CX1 14 CX2
Reference Oscillator VCX1 VCX2
CAV414
VLPOUT VM
9 8 R1 7 R2 10
VCC OUT
IA
VDIFF
Integrator 1 Integrator 2
OP
Signal Conditioning V CX,DIFF
GND Voltage/Current Reference
11 CREF
R01 15 CL1
R02 13 CL2 4 RL1 RL2 5 6 CVM
2 RCX1
3 RCX2
1 ROSC
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 COSC drives two symmetrically built integrators synchronously to its clock and its phase. The capacitors CX1 and CX2 determine the amplitude of the two driven integrators. The difference of the integrator amplitudes gives the relative change of the capacities CX1 and CX2 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 RCX1 or RCX2 for the case that the varying capacitance CX2 has nearly the same (and its smallest) value as the fixed capacitance CX1 (reference capacitance). Therefore one of this resistors is varied until the differential voltage VDIFF = VLPOUT - VM is zero: VDIFF = 0 Application Example: The following values are given: * fixed capacitance CX1: * varying capacitance CX2: Calculation: With the equations given in the boundary conditions, the following values for the devices can be calculated: * COSC: * CL1: * CL2: 80pF 10nF 10nF 50pF 50 ... 100pF
If the signal VDIFF is amplified, it has to fulfil the unequation: VDIFF 400mV Detailed calculations are shown in a separately available Application Note.
analog microelectronics
January 2001 5/6
Converter IC for Capacitive Signals
PINOUT
PIN NAME RCOSC RCX1 RCX2 RL LPOUT VM GAIN VOUT VCC GND VREF COSC CL2 CX2 CL1 CX1
CAV414
DESIGNATION Current Definition of Ref. Oscillator Current Adjustment of Cap. Integrator 1 Current Adjustment of Cap. Integrator 2 Gain Adjustment of Lowpass Filter Output of Lowpass Filter Reference Voltage 2V Gain Adjustment Voltage Output Supply Voltage IC Ground Reference Voltage 5V Capacitor of Reference Oscillator Corner Frequency of Lowpass 2 Integrator Capacitor 2 Corner Frequency of Lowpass 1 Integrator Capacitor 1
RCOSC RCX1 RCX2 RL LPOUT VM GAIN VOUT
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
CX1 CL1 CX2 CL2 COSC VREF GND VCC
Figure 3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
DELIVERY
The CAV414 is available in version: * 16-Pin-DIL (samples) * SO 16 (n) (Maximum Power Dissipation PD = 300mW) * Dice on 5" blue foil
PACKAGE DIMENSIONS SO16 (n)
10,06 0,1 1,45 0,1 0,2 0,05 0,2 0,1 0,42 0,07 1,27 0,635 0,3 0-10 6,2 0,2 4,0 + 0,2 - 0,1
2,00
16
1
8
Figure 4
The information provided herein is believed to be reliable; however, Analog Microelectronics assumes no responsibility for inaccuracies or omissions. Analog Microelectronics assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change without notice. No patent rights or licences to any of the circuits described herein are implied or granted to any third party. Analog Microelectronics does not authorise or warrant any Analog Microelectronics product use in life support devices and/or systems.
analog microelectronics
January 2001 6/6

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