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PDF CAV424 Data sheet ( Hoja de datos )
| Número de pieza | CAV424 | |
| Descripción | Converter IC | |
| Fabricantes | Analog Microelectronics | |
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Converter IC for Capacitive Signals
CAV424
FEATURES
• Ratiometric Supply Voltage: 5V ± 5%
• Wide Operating Temperature Range:
–40°C...+85°C
• High Detection Sensitivity of Relative
Capacitive Changes: 5% – 100%
• Detection Frequency up to 2kHz
• Differential Output Signal with Great
Voltage Swing
• Integrated Temperature Sensor
• Adjustable with only two Resistors
APPLICATIONS
• Industrial Process Control
• Distance Measurement
• Pressure Measurement
• Humidity Measurement
• Level Control
BLOCK DIAGRAM
GENERAL DESCRIPTION
The CAV424 is an integrated C/V converter and
contains the complete signal processing unit for
capacitive signals on chip. The CAV424 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 dif-
ferential voltage output signal can be directly
connected to a following A/D converter or an-
other signal conditioning IC from Analog Mi-
croelectronics. Using the integrated temperature
sensor, digital adjustable systems can be built
easily.
DELIVERY
• DIL16 packages
• SO16(n) packages
• Dice put on 5“ blue foil
www.DataSheet4U.com
CAV424
VTEMP
7
T Sensor
COSC
12
Reference
Oscillator
CX1
16
CX2
14
Integrator 1
Integrator 2
RCX1 RCX2 RCOSC
231
VCC
11
Current Reference
Signal Conditioning
6
VM
5
LPOUT
10 15
GND CL1
13 4
CL2 RL
Figure 1: block diagram CAV424
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 2002
1/7
Rev. 1.3
1 page  
Converter IC for Capacitive Signals
CAV424
where ∆VOSC is the difference between the thresholds (VOSC,HIGH and VOSC,LOW) of the internal reference
oscillator. ∆VOSC is defined via internal resistances and has a value of 2.1V @ VCC = 5V. The oscillator
voltage curve is shown in Figure 2.
Capacitive integrators
The built-in capacitive integrators function in much the same way as the reference oscillator. One
difference lies in the discharge time, which here is twice as long as the charge-up period. Furthermore,
the discharge voltage is clamped to an internal fixed voltage, VCLAMP. The signal voltage of capacitances
CX1 and CX2 is outlined in Figure 3.
The capacitive integrator current ICX is set by external resistance RCX and reference voltage VM:
ICX
=
VM
RCX
Capacitance CX is charged up to maximum voltage VCX and can be calculated as follows:
( )VCX
=
2⋅
fOSC ⋅
CX
I CX
+ C X ,PAR,INT
+ C X ,PAR,EXT
+ VCLAMP
The two voltages across capacitances CX1 and CX2 are subtracted from one another. Applied to the
reference voltage VM the resulting differential voltage is:
( )VCX ,DIFF = VCX1 − VCX 2 + VM
Differential voltage VCX,DIFF is applied to a second-order low-pass filter. The 3dB cut-off frequencies
of the two stages, fC1 and fC2, are defined by external capacitances CL1 and CL2 and internal resistances
R01 and R02 (typically 20kΩ). The 3dB cut-off frequencies must be selected with regard to the reference
oscillator frequency fOSC and the required detection frequency of the overall sensor system (fDET). Here,
the following inequality of the various frequencies must be adhered to:
www.DataSheet4fUD.EcTom< f C << fOSC
The external capacitance for the required cut-off frequency fC amounts to
1
CL = 2π ⋅ R0 ⋅ fC
The output signal of the low-pass filter tracing the ideal curve shown in Figure 3 is calculated as
VLPOUT = VDIFF ,0 + VM
with
( )VDIFF ,0
=
3⋅
8
VCX 1
−VCX 2
Should the differential output voltage VDIFF,0 be too small it can be amplified using the non-inverting
output amplifier, with the degree of amplification being determined by resistances RL1 and RL2.
The amplification of the stage is
GLP
=1+
RL1
RL2
analog microelectronics
January 2002
5/7
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet CAV424.PDF ] | |
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