CAV444

Online Datasheet

Read CAV444 online.

CAV444 AD | Alldatasheet

Document overview

Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
PDF pages: 12

Technical content

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 1/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de PRINCIPLE FUNCTION Capacitance/Voltage converter IC with an adjustable, differential output and temperature detection Typical applications CAV444 is an integrated capacitance-to-voltage transducer. The IC is particularly suitable for all measurements designed to convert a capacitive input signal into a voltage that is direct proportional to the change in the capacitance to be measured. It can be used for:

Measurement of humidity
Level sensing
Material identification
Object detection
The IC can be used as an input circuit for microprocessors or as a stand-alone IC CAV444 8mV / K V = 5 V 5 %CC ± V= 2 , 5 OUT 1,4V± Measurment capacitor (18 pF bis 2.2 nF) Temperature

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 2/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de

PRINCIPLE OF MEASUREMENT 4 HOW CAV444 WORKS 4 TRANSFER FUNCTION (FULL-SCALE OUTPUT SIGNAL) 5 TRANSFER FUNCTION (WITH ADDITIONAL OFFSET ADJUSTMENT) 6 OUTPUT VOLTAGES 8 THE DIMENSIONING PROCESS 8 INITIAL OPERATION 8 STANDARD DIMENSIONING 10 BOUNDARY CONDITIONS 10 APPLICATIONS 11 BLOCK DIAGRAM AND PINOUT 11 DELIVERY 11 ADDITIONAL EQUIPMENT 12 FURTHER READING 12 NOTES 12

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 3/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de

FEATURES

Differential output signal
Wide capacitor measuring range: 18 pF to 2.2 nF
Linear transfer behavior
Adjustable offset voltage
Adjustable full-scale signal
Detection frequency: 15 Hz to 1.9 kHz
Measurement oscillator frequency: 1 kHz to 130 kHz
Wide dynamic range detection
Wide temperature range: -40°C...+85°C
Simple calibration (Excel program)
RoHS compliant BLOCK DIAGRAM CAV444 is an integrated C/V transducer that contains full signal conditioning electronics for the linear conversion of capacitive input sig- nals into a suitable differential output voltage. It also has an additional temperature detector. The output signal is proportional to the change in capacitance ∆C M = CM,max – CM,min. A differential voltage referenced to internal reference voltage VREF is generated as an output signal. This output voltage has been specially designed for connection to a following A/D converter. As this is an analog circuit, its resolution are only limited by noise. Together with the inte grated temperature sensor of the CAV444 and a processor, electronically calibratable systems can be assembled. A simple Excel software program eases the dimensioning of CAV444. VCC VREF CW C1F GND VBVTEMP GAIN VOUT CM CA V444 Supply Lowpass filter Output stage CF2 f/V converter Measurement oszillator Temperature- Sensor RCW RCM RA Figure 1: Block diagram of CAV444

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 4/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de PRINCIPLE OF MEASUREMENT CAV444 is an integrated C/V (capacitance-to-volta ge) converter circ uit that contains full signal conditioning and evaluation electronics for linear, capacitive signal sources. The principle of measurement behind CAV444 is the conversion of a change in capacitance (measurement capacitor, C M) into a linear, differential outpu t voltage. Measurement capacitor C M can be altered by the amount ∆CM = CM,max – CM,min (CM,min is the basic capacitance of CM). HOW CA V444 WORKS The CAV444 IC functions according to the followi ng principle. The measurement capacitor is the capacitor of an internal measurem ent oscillator. This generates the clock pulse with which the measurement capacitor is charged and discharged. The number of clock pulses provided depends on the measurement capacitor. These are converted into a DC voltage signal in the f/V converter and in the backend lowpass filter. The filtered DC voltage signal travels to an adjustable amplifier stage that enables the output signal to be set to the required value. CA V444 Supply Lowpass filter Output- stage f/V converter Measurement oszillator Temperature- Sensor RA CM 41316 152 VCC VREF CW C 1 F GND VBVTEMP GAIN VOUT CM CF2RCW RCM RA Figure 2: Block diagram of CAV444 with signal patterns

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 5/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de TRANSFER FUNCTION (FULL-SCALE OUTPUT SIGNAL) Transfer function V OUT* for the CAV444 full-scale output signal is expressed as: REFDIFFOUT VVV += ** (1) where VREF = reference voltage and TPASLPDIFF VGV ⋅=* (2) The following applies to GLP: 11 R RGLP += (3) and to the output voltage after the lowpass: CWW CMCMM TPAS RC RVCV ⋅⋅ ⋅∆⋅⋅= 8 3 (4) with VVCM 1.2=∆ . VCC VRE F CW CF1 VB VOU T CA V444 Supply Lowpass filter Output- stage CF2 f/V converter Measurement oszillator Temperature- Sensor RCW RA CM RCM VREF CVR EF VCC VREF CW C1F GND VBVTEMP GAIN VOUTCM CF2RCW RCM RA Figure 3: CAV444 with circuitry for full-scale adjustment

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 6/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Equation (2) implies that signal VTPAS is amplified by an internal operational amplifier in the output stage, where gain GLP can be determined by resistors R1 and R2. Resistor RA is used to set the supply for the f/V converter. Pin VB is for internal bi asing and must be connected up to supply voltage VCC. With equations (3) and (4) incorporated into (2), the transfer function for the full-scale signal (1) is accrued as: REF CWW CMCMM REFTPASLPREFDIFFOUT VRC RVC R RVVGVVV +  +=+⋅=+= 8 31** 1 (5) where 6.1 max,M W CC = . The resistors are defined by the respective load currents and have fixed values of RCM = 250kΩ and RCW = 500kΩ. We can see that the output voltage is a linear ly dependent function of measurable variable C M (VOUT* = f(CM)), as all other variables are fixed by the dimensioning process. In Figure 4 we can recognize that the output signal is raised by V REF. In order to be able to fix the offset, the network must be extended. TRANSFER FUNCTION (WITH ADDITIONAL OFFSET ADJUSTMENT) When setting the output signal the adjustability of the offset must be taken into account with the transfer function (5). With regard to Figure 5, the transfer function is calculated as: REFTPASREFDIFFOUT VBVAVVV ⋅+⋅=+= ( 6 ) VOUT CM CM Min CM Max VREF 2,5V CM Figure 4: Output signal VOUT* referenced to ground

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 7/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de with the setup coefficient for span as A and the setup coefficient for the offset as B: ))(( ))()(())(( 543542 521524213521524 RRRRRR RRRRRRRRRRRRRRRA ++ +++++++= and (7) ))(( )2)2(2()2( 543542 52514212135421 RRRRRR RRRRRRRRRRRRRR ++++++ (8) In the transfer equation resistors R1 and R3 used to set the span and offset are variable. They are calculated in the Excel program Kali_CAV444.xls. R2, R4 and R5 are fixed 100kΩ resistors. We can see that the output voltage is a linearly de pendent function of measurable variable CM (VOUT = f(CM)), as all other variables are fixed by the dimensioning process and equation (5). VCC VRE F CW CF1 VB VOU T CA V444 Versorgung Lowpass filter Output- stage CF2 f/V converter Measurement oszillator Temperature- Sensor RCW RA CM RCM VRE F VCC GND CV REF VCC VREF CW C1F GND VBVTEMP GAIN VOUTCM CF2RCW RCM RA Figure 5: Full circuit with adjustable full-scale output signal and adjustable offset signal

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 8/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de OUTPUT VOLTAGES The following applies to the output voltage: REFDIFFOUT VVV += THE DIMENSIONING PROCESS Excel program Kali_CAV444.xls should be used for dimensioning purposes. The dimensioning process for CAV444 assumes that in addition to measurement capacitor CM and the f/V converter capacitor CW, parasitic capacitances in both the IC and measurement circuit also influence the signal pattern. For this reason the offset and full scale are ca librated based on the installed system, where all parasitic capacitances and exemplary variations in the components used have been taken into account. Taking transfer function (6) as its basis, the Excel spreadsheet Kali_CAV444.xls [1] first computes suitable values for a measurement operating point. Th e circuit output is measur ed at this point and these measurements then entered into the program in stage two of the procedure. The algorithm calculates the two adjusting resistors required to calibrate the system. Once these have been placed in the circuit, the calibration of both offset and span is complete. INITIAL OPERATION Initial operation is described in detail in th e description of the ca libration program (see Kali_CAV444.xls). VOU T (Volt) V OUT , ma x V OUT , mi n VRE F +VDI FF -VDIFF VCC 2, 5 Figure 6: Maximum output voltage VOUT

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 9/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de ELECTRICAL SPECIFICATIONS Tamb = 25°C, VCC = 5 V (unless otherwise stated) Parameter Symbol Conditions Min. Typ. Max. Unit Supply Supply Voltage VCC Ratiometric range 4.75 5.00 5.25 V Temperature Specifications Operating Tamb -40 105 °C Storage Tst -55 125 °C Measurement Oscillator Measurement Capacitor Range CM ICM = 10µA 18 2200 pF Oscillator Frequency Range fM 1 130 kHz Oscillator Current ICM RCM = 250kΩ 9.5 10 10.75 µA Detection Frequency fSIG 1.9 kHz f/V Converter Converter Capacitor Range CW CW = CM,max / 1.6 ICW = 5 µA 11.25 1375 pF Capacitive Charge Current ICW RCW = 500 kΩ 4.75 5 5.38 µA Lowpass Stage Adjustable Gain GLP 1 10 Output Voltage VOUT Vout = VDiff + VREF 1.1 VCC – 1.1 V Corner Frequency 1 fCF1 R01 = 20 kΩ, CF1 = 1 nF 8 kHz Corner Frequency 2 fCF2 R02 = 20 kΩ, CF2 = 1 nF 8 kHz Resistive Load at pin VOUT RL 200 kΩ Capacitive Load at pin VOUT CL 50 pF Output Voltage Shift VDIFF VM = 2.5 V -1.4 1.4 V Temperature Coefficient VDIFF (together with Input Stages) dVDIFF /dT Tamb = -40...+105°C ±100 ppm/°C Internal Resistors 1 and 2 R01, R02 20 kΩ Temperature Coefficient R01,02 d R01,02 /dT Tamb = -40...+105°C 1.9 10 -3/°C Ratiometric Error of VOUT RAT@VDIFF* 0.11 % FS Voltage Reference VREF Voltage VREF Ratiometric to V CC 2.5 V VREF vs. Temperature d VREF /dT Tamb = -40...+105°C ±20 ±50 ppm/°C Current IVREF Source 16 µA IVREF Sink -16 µA Load Capacitance CVREF 80 100 120 nF Ratiometric Error of VREF RAT@VREF* 0.007 % FS * RAT @ VDIFF = 2 [1.05 VDIFF(VCC = 5V) – VDIFF(VCC = 5.25V)]/[VDIFF(VCC = 5V) + VDIFF(VCC = 5.25V)] ** RAT @ VM = 2 [1.05 VM(VCC = 5V) – VM(VCC = 5.25V)]/[VM(VCC = 5V) + VM(VCC = 5.25V)]

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 10/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de Parameter Symbol Conditions Min. Typ. Max. Unit Temperature Sensor VTEMP Voltage VTEMP RTEMP ≥ 50M 2.20 2.32 2.45 V Sensitivity d VTEMP/dT RTEMP ≥ 50M 8 mV/°C Thermal Nonlinearity RTEMP ≥ 50M, end point method 0.5 % FS Table 1: Electrical specifications for CAV444 Notes: 1) Currents flowing into the IC are negative. 2) RTEMP is the minimum possible load resistance at pin VTEMP. In order to achieve as good a temperature behavior as possible, it is essential that resistors RCM and RCW have the same temperature coefficients and that they are placed very close together in the circuit. STANDARD DIMENSIONING Parameter Symbol Min. Typ. Max. Unit Output Stage Resistors (1%) R2 , R4 , R5 100 kΩ Full-Scale Resistor (0.1%), Calibration Start Value* R1 33 kΩ Offset Resistor (0.1%), Calibration Start Value* R3 100 kΩ f/V-Stage Biasing Resistor RA 240 kΩ Measurement Oscillator Resistor RCM 250 kΩ f/V-Stage Filter Resistor RCW 500 kΩ Filter Capacitors (vary with value of CM,min)** CF1 ,CF2 3.8 440 nF Reference Voltage Capacitor (VREF = 2.5V) CVREF 80 100 120 nF Table 2: Standard values for external components

*) R1 and R3 are the initial values given at the start of the calibration process (Kali_CAV444.xls). During calibration, these are replaced by precisely computed, individual values.
**) CF1 and CF2 are dimensioned by the calibration program. BOUNDARY CONDITIONS Parameter Symbol Condition Min. Typ. Max. Unit Maximum Supply Voltage VCCmax 17 V Oscillator Frequency Range fOSC 1 130 kHz f/V Converter Current ICW RCW = 500 kΩ 5.38 µA Measurement Oscillator Current ICM RCM = 250 kΩ 10.75 µA Table 3: Boundary conditions

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 11/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de

APPLICATIONS

Example applications are generated by dimensioning the circuit in Figure 5 with the help of the calibration program Kali_CAV444.xls [1] BLOCK DIAGRAM AND PINOUT Table 4: CAV444 Pin out DELIVERY CAV444 is available as:

An SO16 (n); see data sheets: package
For sample batches CAV444 can be supplied on a DIL16 SO16 adapter (CAV444Adapt) PIN NAME DESCRIPTION

1 RCM Current setting for the measurement oscillator

2 RCW Current setting for the f/V converter

3 VB Bias voltage Æ VCC

4 GAIN Gain setting

5 VOUT Output voltage

6 VREF Reference voltage 2.5 V

7 VTEMP Temperature sensor output

8 N.C. Not connected 9 N.C. Not connected

10 GND IC ground

11 VCC Supply voltage

12 CM Measurement capacitor/measurement oscillator

13 CF2 Lowpass capacitor 2, corner frequency 2

14 RA Stabilizing resistor for f/V converter

15 CF1 Lowpass capacitor 1, corner frequency 1

16 CW f/V converter capacitor

N.C. VB CW CF1 RA CF2 CM VCC GND N.C. CAV 444 Figure 10: CAV444 Pin out

CAV444 – C/V transmitter IC with adjustable output voltage for capacitive input signals Analog Microelectronics GmbH An der Fahrt 13, D – 55124 Mainz Mai 2010 - Rev 1.1 - Page 12/12 Phone: +49 (0)6131/91 0730-0 Fax: +49 (0)6131/91 073-30 Internet: http://www.analogmicro.de Email: info@analogmicro.de ADDITIONAL EQUIPMENT For design purposes, by way of support Analog Microelectronics can also supply a starter kit which consists of a breadboard ( BBCAV444) (which has been assembled for a specific set of parameters but which can also be used for individual meas urements), a description and the spreadsheet Kali_CAV444. FURTHER READING Please see our website for further information (www.analogmicro.de): [1] http://www.analogmicro.de/english/index.html - Kali_CAV444.pdf NOTES

Product Information

CAV444 specifications and overview.

Summary

C/V transmitter IC with adjustable output voltage for capacitive input signals

Description