CAV444 Datasheet, PDF (7/12 Pages) Analog Devices – C/V transmitter IC with adjustable output voltage for capacitive input signals

CAV444 – C/V transmitter IC
with adjustable output voltage
for capacitive input signals
with the setup coefficient for span as A and the setup coefficient for the offset as B:
A = ^{R4 (R2 R5 + R1 (R2 + R5 )) + R3 ((R1 + R2 )R4 + R2 R5 + R1 (R2 + R5 ))} and
(7)
R₂ (R₄ R₅ + R₃ (R₄ + R₅ ))
B = ^{(R1 + 2R2 )R4 R5 + R3 (2R1R2 + (R1 + 2R2 )R4 + R1R5 + 2R2 R5 )}
(8)
R₂ (R₄ R₅ + R₃ (R₄ + R₅ ))
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 dependent function of measurable variable C_M
(V_OUT = f(C_M)), as all other variables are fixed by the dimensioning process and equation (5).
VTEMP
7
GND
10
R_A
RA
14
V_CC
V_B
VCC VB
11
3
CM
12
C_M
RCM
1
Temperature-
Sensor
Measurement
oszillator
CAV444
Versorgung
f/V
converter
Lowpass
filter
Output-
stage
R_CM
16 2
15 13
4
CW
RCW CF1 CF2
GAIN
C_W
R C _CW
F1
C_F2
VREF V_REF
6
C_VREF
VOUT ^VOUT
5
V_CC
R₁
R₃
R₂ ^R5
V_REF
R₄
GND
Figure 5: Full circuit with adjustable full-scale output signal and adjustable offset
signal
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Phone: [phone]
Fax: [phone]
Internet: http://www.analogmicro.de
Email: [e-mail]
Mai 2010 - Rev 1.1 - Page 7/12