CAV424 Datasheet, PDF (5/16 Pages) List of Unclassifed Manufacturers – Converter IC for Capacitive Signals

CAV424 - C/U transducer IC
with adjustable output voltage
If capacitors C_M and C_R are the same, following rectification and filtering (see Figure 5) a DC-
voltage signal is generated with a value of 0. Should C_M change (measurement capacitor), a DC-
voltage signal is produced which is proportional to !C_M .
If C_M and C_R are not the same, when !C_M = 0 an offset would be generated at the output which is
superimposed onto the actual direct voltage signal.
Oscillator function
The integrated oscillator charges up and then discharges the external oscillator capacitor C_OSC (see
Figure 3).
The oscillator current I_OSC is determined by external resistor R_OSC and reference voltage V_M:
I_OSC
"
V_M
R_OSC
(1)
The oscillator frequency f_OSC is calculated ^VOSC
as:
V_OSC,HIGH
f _OSC
"
I _OSC
2 # $V_OSC # C_OSC
(2)
where $V_OSC is the difference between
V_OSC
(2)
V_OSC,LOW
the thresholds of the internal oscillator
(V_OSC,HIGH and V_OSC,LOW). $V_OSC is
defined via internal resistors in the IC and
T
T
2
2T ^{time t}
has a value of 2.1V @ V_CC = 5V (see _{Figure 3: Oscillator voltage curve}
Figure 3). The oscillator frequency can
thus be specified by the choice of R_OSC and C_OSC; the relevant maximum and minimum values are
given in Table 1.
Capacitive integrators
The built-in capacitive integrators function works in the same way as the oscillator. One difference
lies in the discharge time, which here is half the length of the charge-up period. Furthermore, the
minimum oscillator voltage for the integrators is internally clamped to a value of V_CLAMP = 1.2 V
(see Figure 4).
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
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July 2007 - Rev 1.2 - Page 5/16