Ratiometric Supply Voltage: Wide Operating Temperature Range: -40°C.+8

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Ratiometric Supply Voltage: Wide Operating Temperature Range: -40°C.+8

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Converter Capacitive Signals
Ratiometric Supply Voltage: Wide Operating Temperature Range: -40°C.+85°C High Detection Sensitivity Relative Capacitive Changes: 100% Detection Frequency 2kHz Differential Output Signal with Great Voltage Swing Integrated Temperature Sensor Adjustable with only Resistors
CAV424
GENERAL DESCRIPTION
CAV424 integrated converter contains complete signal processing unit capacitive signals chip. CAV424 detects relative capacitive change measuring capacity fixed reference capacity. optimised capacities wide range 10pF with possible changes capacity 100% reference capacity. differential voltage output signal directly connected following converter another signal conditioning from Analog Microelectronics. Using integrated temperature sensor, digital adjustable systems built easily.
APPLICATIONS
Industrial Process Control Distance Measurement Pressure Measurement Humidity Measurement Level Control
DELIVERY
DIL16 packages SO16(n) packages Dice blue foil
BLOCK DIAGRAM
VTEMP
RCX1 RCX2 RCOSC
CAV424
Sensor Current Reference
COSC
Reference Oscillator
Integrator Integrator Signal Conditioning
LPOUT
Figure block diagram CAV424
analog microelectronics
Analog Microelectronics GmbH Fahrt 55124 Mainz Internet: http://www.analogmicro.de Phone: (0)6131/91 Fax: (0)6131/91 E-mail: info@analogmicro.de
August 2001 Rev.
Converter Capacitive Signals
ELECTRICAL SPECIFICATIONS
Tamb 25°C, (unless otherwise noted)
Parameter Supply Supply Voltage Maximum Supply Voltage Quiescent Current Temperature Specifications Operating Storage Junction Thermal Resistance Tamb DIL16 plastic package SO16 plastic package COSC ROSC 250k VCCmax Tamb 85°C, ratiometric range 4.75 5.00 Symbol Conditions Min. Typ.
CAV424
Max.
Unit
5.25
°C/W °C/W
Reference Oscillator Oscillator Capacitor Range Oscillator Frequency Range Oscillator Current Capacitive Integrator Capacitor Range Capacitive Integrator Current Capacitor Detection Sensitivity Capacitor Range Capacitive Integrator Current Detection Frequency Lowpass Adjustable Gain Output Voltage Corner Frequency Corner Frequency Resistive Load LPOUT Capacitive Load LPOUT Temperature Coefficient VDIFF (together with Input Stages) Internal Resistor Temperature Coefficient R01,02 Ratiometric Error VLPOUT VLPOUT RLOAD CLOAD dVDIFF R01, dR01,02 RAT@VDIFF* Tamb 85°C VDIFF VLPOUT Tamb 85°C ±100 0.11 20k, =1nF 20k, =1nF ppm/°C 10-3/°C fDET RCX1 500k (CX2 )/CX1 RCX2 500k =1nF 4.75 10.5 4.75 1000 5.38 2000 5.38 COSC fOSC IOSC 1800 10.75
VDIFF [1.05 VDIFF(VCC VDIFF(VCC 5.25V)]/[VDIFF(VCC VDIFF(VCC 5.25V)]
analog microelectronics
August 2001
Converter Capacitive Signals
Parameter Voltage Reference Voltage Temperature Current Load Capacitance Ratiometric Error Temperature Sensor VTEMP Voltage Sensitivity Thermal Nonlinearity VTEMP dVTEMP/dT RTEMP RTEMP RTEMP 50M, point method 2.20 2.32 RAT@VM** Tamb -40.+85°C Source Sink 0.007 Symbol Conditions Min. Typ.
CAV424
Max. Unit
ppm/°C
2.45
mV/°C
[1.05 VM(VCC VM(VCC 5.25V)]/[VM(VCC VM(VCC 5.25V)]
Note: oscillator capacity chosen following way: COSC capacitor range extended whereby system performance reduced electrical limits exceeded. Currents flowing into negative. RTEMP maximum load resistance VTEMP
BOUNDARY CONDITIONS
Parameter Current Definition Ref. Oscillator Current Adjustment Cap. Integrator Current Adjustment Cap. Integrator Output Stage Resistor Reference Voltage 2.5V (only internal use) Lowpass Capacitance Lowpass Capacitance Oscillator Capacitance Symbol RCOSC RCX1 RCX2 COSC Min. 100CX1 100CX1 COSC =1.55CX1 200CX1 200CX1 COSC =1.60CX1 COSC =1.65CX1 Typ. Max. Unit
Note: system performance over temperature forces that resistors RCX1, RCX2 ROSC have same temperature coefficient very close placement them circuit. capacities CX1, COSC also forced have same temperature coefficient very close placement them circuit.
FUNCTIONAL DESCRIPTION
CAV424 functions according following principle. variable reference oscillator, whose frequency capacitance COSC, drives symmetrical integrators which phase-locked clock-synchronised. amplitudes driven integrators determined capacitances CX2, where designated (measurement signal) reference capacitance measurement signal capacitance. With high common-mode rejection ratio high resolution, com-
analog microelectronics
August 2001
Converter Capacitive Signals
CAV424
parison amplitudes proV duces signal which corresponds change capacitance relative another. This difference signal rectified ensuing pass. filtered signal transferred differential, adjustable output stage. Individual circuit variables, such filter constants Time amplification, with just external components. using Figure oscillator voltage curve integrators their capacitances CX2, swings capacitance 100% relation measurement reference capacitance measured. varied range range measurement measurement signal capacitance 0-10.5
OSC,HIGH OSC,LOW
capacitive sensor functions whose signal conditioned with CAV424 described detail following section. Simple dimensional requirements given, permitting sensor system assembled. CAV424 reference oscillator reference oscillator charges then discharges external oscillator capacitance COSC, internal parasitic capacitance COSC,PAR,INT, external parasitic capacitance COSC,PAR,EXT (from printed board assembly, example). Oscillator capacitance COSC dimensioned follows: COSC where fixed capacitance (reference capacitance) capacitive sensing element.
VOSC
VCX1 VCX2
VCLAMP
Time
Figure integrator voltage curve
reference oscillator current IOSC determined external resistance ROSC reference voltage ROSC
frequency reference oscillator fOSC given VOSC (COSC COSC COSC
analog microelectronics
August 2001
Converter Capacitive Signals
CAV424
where VOSC difference between thresholds (VOSC,HIGH VOSC,LOW) internal reference oscillator. VOSC defined internal resistances value 2.1V oscillator voltage curve shown Figure Capacitive integrators built-in capacitive integrators function much same reference oscillator. difference lies discharge time, which here twice long charge-up period. Furthermore, discharge voltage clamped internal fixed voltage, VCLAMP. signal voltage capacitances outlined Figure capacitive integrator current external resistance reference voltage Capacitance charged maximum voltage calculated follows: VCLAMP voltages across capacitances subtracted from another. Applied reference voltage resulting differential voltage ,DIFF (VCX
Differential voltage VCX,DIFF applied second-order low-pass filter. cut-off frequencies stages, fC2, defined external capacitances internal resistances (typically 20k). cut-off frequencies must selected with regard reference oscillator frequency fOSC required detection frequency overall sensor system (fDET). Here, following inequality various frequencies must adhered external capacitance required cut-off frequency amounts output signal low-pass filter tracing ideal curve shown Figure calculated VLPOUT VDIFF with VDIFF (VCX Should differential output voltage VDIFF,0 small amplified using non-inverting output amplifier, with degree amplification being determined resistances RL2. amplification stage
analog microelectronics
August 2001
Converter Capacitive Signals
thus follows that output signal low-pass stage VLPOUT VDIFF with VDIFF VDIFF (VCX
CAV424
order reduce number external components needed sensor system temperature acquisition sensor integrated. With processor, this sensor used compensate temperature error entire sensor system, example.
FUNCTIONAL DIAGRAM
RCX1 RCX2 ROSC
CAV424
Sensor Current Reference COSC Reference Oscillator
Integrator Integrator
Signal Conditioning
VDIFF
Figure functional diagram CAV424 Adjustment: zero-adjustment made resistors RCX1 RCX2 case that varying capacitance nearly same (and smallest) value fixed capacitance (reference capacitance). Therefore this resistors varied until differential voltage VDIFF VLPOUT zero: VDIFF
analog microelectronics
August 2001
Converter Capacitive Signals
Application Example: following values given: fixed capacitance CX1: varying capacitance CX2: Calculation: 50pF 100pF
CAV424
With equations given boundary conditions, following values devices calculated: COSC: CL1: CL2: 80pF 10nF 10nF
PINOUT
NAME RCOSC RCX1 RCX2 LPOUT VTEMP N.C. N.C. COSC DESRIPTION Current Definition Ref. Oscillator Current Adjustment Cap. Integrator Current Adjustment Cap. Integrator Gain Adjustment Output Reference Voltage 2.5V Temperature Sensor Connected Connected Ground Supply Voltage Capacitor Reference Oscillator Corner Frequency Lowpass Integrator Capacitor Corner Frequency Lowpass Integrator Capacitor
RCOSC RCX1 RCX2 LPOUT VTEMP N.C.
COSC N.C.
Figure pinout CAV424
DELIVERY
CAV424 available version:
(maximum power dissipation 300mW) Dice blue foil
information provided herein believed reliable; however, Analog Microelectronics assumes responsibility inaccuracies omissions. Analog Microelectronics assumes responsibility this information, such information shall entirely user's risk. Prices specifications subject change without notice. patent rights licences circuits described herein implied granted third party. Analog Microelectronics does authorise warrant Analog Microelectronics product life support devices and/or systems.
analog microelectronics
August 2001

Ratiometric Supply Voltage: Wide Operating Temperature Range: -40°C.+8

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