Converter IC for Capacitive Signals CAV414 FEATURES GENERAL DESCRIPTION • 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 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 CAV414 Reference Oscillator 12 16 VOUT IA CX1 8 OP Integrator 1 CX2 14 VCC 9 7 Integrator 2 GAIN GND 10 Signal Conditioning Voltage/Current Reference 15 CL1 13 CL2 4 5 6 RL LPOUT VM 2 3 11 VREF 1 RCX1 RCX2 RCOSC Figure 1 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: [email protected] January 2001 1/6 Rev. 2.1 Converter IC for Capacitive Signals CAV414 ELECTRICAL SPECIFICATIONS Tamb = 25°C, VCC = 24V, IREF = 1mA (unless otherwise noted) Parameter Symbol Conditions Min. Typ. Max. Unit 35 V 1.55 2.7 mA Supply Supply Voltage VCC Quiescent Current ICC 6 Tamb = –40 ... 85°C, IREF = 0mA Temperature Specifications Operating Tamb –40 85 °C Storage Tst –55 125 °C Junction Tj Thermal Resistance Θja DIL16 plastic package 70 °C/W Θja SO16 (n) plastic package 140 °C/W Oscillator Capacitor Range COSC COSC = 1.6 ⋅ CX1 14 Oscillator Frequency Range fOSC Oscillator Current IOSC ROSC = 200kΩ 9.5 150 °C Reference Oscillator 1 10 1800 pF 130 kHz 10.75 µA 1000 pF 5.38 µA 100 % Capacitive Integrator 1 and 2 Capacitor Range 1 CX1 10 Capacitive Integrator Current 1 IX1 RCX1 = 400kΩ Capacitor Detection Sensitivity ∆ CX ∆ CX = (CX2 − CX1 )/CX1 5 Capacitor Range 2 CX2 CX2 = CX1 ⋅ (1 + ∆ CX ) 10.5 Capacitive Integrator Current 2 IX2 RCX2 = 400kΩ 4.75 Detection Frequency fDET CL1 = CL2 =1nF 4.75 5 5 2000 pF 5.38 µA 2 kHz Lowpass Adjustable Gain GLP Output Voltage VLPOUT Corner Frequency 1 fC1 Corner Frequency 2 fC2 1 10 VM –0.4 VM +0.4 V R01 = 20kΩ, CL1 =1nF 10 kHz R02 = 20kΩ, CL2 =1nF 10 kHz Resistive Load at PIN LPOUT RLOAD Capacitive Load at PIN LPOUT CLOAD 200 Temperature Coefficient VDIFF (together with Input Stages) dVDIFF /dT Internal Resistor 1 and 2 R01, R02 Temperature Coefficient R01,02 dR01,02 /dT Tamb = –40 ... 85°C Power Supply Rejection Ratio (together with Input Stages) PSRR IOUT ≤ 1mA kΩ 50 pF ±100 ppm/°C 20 kΩ 1.9 10-3/°C 80 90 dB 5 VDIFF = VLPOUT - VM , Tamb = –40 ... 85°C Voltage Reference VREF Voltage VREF 4.75 Current IREF 0 VREF vs. Temperature dVREF /dT Line Regulation Load Regulation ±90 V 9 mA ±140 ppm/°C dVREF /dV Vcc = 6V...35V 30 80 ppm/V dVREF / dV Vcc = 6V...35V, IREF ≈ 4mA 60 150 ppm/V 0.05 0.10 %/mA 0.06 0.15 %/mA 2.2 5.0 µF dVREF /dI dVREF /dI Load Capacitance Tamb = –40...+85°C 5.25 IREF ≈ 4mA CREF analog microelectronics 1.9 January 2001 2/6 Converter IC for Capacitive Signals Parameter Symbol Conditions Min. CAV414 Typ. Max. 2 2.15 Unit Voltage Reference VM Voltage VM VM vs. Temperature dVM /dT Tamb = –40...+85°C IVM Source 5 µA IVM Sink -5 µA 120 nF Current Load Capacitance 1.90 V ppm/°C ±90 CVM 80 100 Internal Gain GIA 4.9 5 Differential Range VIN 0 400 mV Common Mode Input Range CMIR VCC < 9V, ICV < 2mA 1.5 VCC - 3 V CMIR VCC ≥ 9V, ICV < 2mA 1.5 Instrumentation Amplifier Input Stage Common Mode Rejection Ratio CMRR Power Supply Rejection Ratio PSRR Offset Voltage VOS VOS vs. Temperature dVOS /dT 80 IOUT ≤ 1mA 80 5.1 6.0 90 90 ±1.5 V dB dB ±6 mV µV/°C ±5 Output Stage Adjustable Gain GOP Input Range IR 1 IR VCC ≥ 11V 0 Power Supply Rejection Ratio PSRR IOUT ≤ 1mA 80 Offset Voltage VOS ±0.5 ±2 mV VOS vs. Temperature dVOS /dT ±3 ±7 µV/°C Input Bias Current IB 10 25 nA IB vs. Temperature dIB /dT 7 20 pA/°C Output Voltage Range VOUT VCC < 19V 0 VCC - 5 V VOUT VCC ≥ 19V 0 14 V Output Current Limitation ILIM VCC ≥ 10V 5 10 mA Output Current IOUT 0 ILIM mA Load Resistance RL 2 Load Capacitance CL VCC < 11V 0 VCC - 5 6 V 90 7 V dB kΩ 500 nF 35 V Protection Functions Protection Against Reverse Polarity Ground vs. VCC vs. VOUT 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 CAV414 BOUNDARY CONDITIONS Parameter Symbol Min. Typ. Max. Unit Current Definition of Ref. Oscillator RCOSC 190 200 210 kΩ Current Adjustment of Cap. Integrator 1 RCX1 350 400 450 kΩ Current Adjustment of Cap. Integrator 2 RCX2 350 400 450 kΩ RL1 + RL2 90 200 kΩ Lowpass Stage Resistor Sum Output Stage Resistor Sum R1 + R2 90 200 kΩ Reference Voltage 5V CREF 1.9 2.2 5 µF Reference Voltage 2V (only for internal use) CVM 80 100 120 nF Lowpass Capacitance 1 CL1 100⋅CX1 200⋅CX1 Lowpass Capacitance 2 CL2 100⋅CX1 200⋅CX1 Oscillator Capacitance COSC COSC =1.55⋅CX1 COSC =1.60⋅CX1 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 CAV414 Reference Oscillator 12 COSC VLPOUT 16 Integrator 1 14 Integrator 2 VDIFF IA VM VCX1 R1 VCX2 7 R2 CX2 10 Signal Conditioning V CX,DIFF GND Voltage/Current Reference R02 15 CL1 OUT 8 OP CX1 R01 VCC 9 13 CL2 4 5 RL1 6 2 CVM 3 RCX1 11 CREF 1 RCX2 ROSC RL2 Figure 2 analog microelectronics January 2001 4/6 Converter IC for Capacitive Signals CAV414 FUNCTIONAL DESCRIPTION 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: 50pF • varying capacitance CX2: 50 ... 100pF Calculation: With the equations given in the boundary conditions, the following values for the devices can be calculated: • COSC: 80pF • CL1: 10nF • CL2: 10nF 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 CAV414 PINOUT RCOSC 1 16 CX1 RCX1 2 15 CL1 RCX2 3 14 CX2 RL 4 13 CL2 LPOUT 5 12 COSC VM 6 11 GAIN 7 10 VREF GND VOUT 8 9 VCC Figure 3 PIN NAME 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 RCOSC RCX1 RCX2 RL LPOUT VM GAIN VOUT VCC GND VREF COSC CL2 CX2 CL1 CX1 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 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) 4,0 + 0,2 - 0,1 10,06 ± 0,1 1,45 ± 0,1 ≤ 2,00 0,2 ± 0,05 0,2 ± 0,1 ≤ 0,635 1,27 0,42 ± 0,07 ≥ 0,3 0°-10° 6,2 ± 0,2 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