CAV414

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 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 = 25°C, VCC = 24V, IREF = 1mA (unless otherwise noted) Parameter Supply Supply Voltage Quiescent Current Temperature Specifications Operating Storage Junction Thermal Resistance Tamb Tst Tj Θja Θja 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...+85°C 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 ... 85°C IOUT ≤ 1mA 80 VDIFF = VLPOUT - VM , Tamb = –40 ... 85°C ±100 20 1.9 90 R01 = 20kΩ, CL1 =1nF R02 = 20kΩ, CL2 =1nF 200 1 VM –0.4 CX1 IX1 ∆ CX CX2 IX2 fDET RCX1 = 400kΩ ∆ CX = (CX2 − CX1 )/CX1 CX2 = CX1 ⋅ (1 + ∆ CX ) RCX2 = 400kΩ CL1 = CL2 =1nF 10 4.75 5 10.5 4.75 5 5 COSC fOSC IOSC ROSC = 200kΩ COSC = 1.6 ⋅ CX1 14 1 9.5 10 DIL16 plastic package SO16 (n) plastic package 70 140 –40 –55 VCC ICC Tamb = –40 ... 85°C, 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 µA 1000 5.38 100 2000 5.38 2 pF µA % pF µA kHz 10 VM +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 VM Voltage VM vs. Temperature Current VM d VM / d T 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...+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 VCC - 3 6.0 mV V V dB dB ±6 mV µV/°C VCC - 5 6 V V dB ±2 ±7 25 20 VCC - 5 14 10 ILIM 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: 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 RL 1 + RL 2 R1 + R2 CREF CVM CL 1 CL 2 COSC Min. 190 350 350 90 90 1.9 80 100⋅CX1 100⋅CX1 COSC =1.55⋅CX1 2.2 100 200⋅CX1 200⋅CX1 COSC =1.60⋅CX1 Typ. 200 400 400 CAV414 Max. 210 450 450 200 200 5 120 Unit kΩ kΩ kΩ kΩ kΩ µF nF COSC =1.65⋅CX1 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