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MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
33794
7
10
DIS_SHIELD
Shield Driver
This pin is used to turn off the shield signal. The purpose of doing this is to be able
to detect that the shield signal is not working or the connection to the coax shields
is broken. If either of these conditions exists, there will be little or no change in the
capacitance measured when the DIS_SHIELD is asserted. If the SHIELD output
is working and properly connected, the capacitance of the coax will not be
cancelled when this pin is asserted and the measured capacitance will appear to
change by approximately the capacitance between the center conductor and the
shield in the coax.
14–11
A, B, C, D
Selector Inputs
These input pins control which electrode or reference is active. Selection values
are shown in Table 1, Electrode Selection, page 14.
15
SIGNAL
Undetected Signal
This is the undetected signal being applied to the detector. It has a DC level with
the low radio frequency signal superimposed on it. Care must be taken to minimize
DC loading of this signal. A shift of DC will change the center point of the signal
and adversely affect the detection of the signal.
16
LEVEL
Detected Level
This is the detected, amplified, and offset representation of the signal voltage on
the selected electrode. Filtering of the rectified signal is performed by a capacitor
attached to LP_CAP.
17
PWR_MON
Power Monitor
This is connected through a voltage divider to V
PWR
. It allows reduction of the
voltage so it will fall within the range of the ADC on the MCU.
18
LP_CAP
Low-Pass Filter Capacitor
A capacitor on this pin forms a low pass filter with the internal series resistance
from the detector to this pin. This pin can be used to determine the detected level
before amplification or offset is applied. A 10 nF capacitor connected to this pin will
smooth the rectified signal. More capacitance will increase the response time
unnecessarily.
19
R_OSC
Oscillator Resistor
A resistor from this pin to circuit ground determines the operating frequency of the
oscillator. The 33794 is optimized for operation around 120 kHz.
24
CLK
Clock
This pin provides a square wave output at the same frequency as the internal
oscillator. The edges of the square wave coincide with the peaks (positive and
negative) of the sine wave.
25
V
DD_
MON
V
DD
Monitor
This is connected through a voltage divider to V
DD
. It allows reduction of the
voltage so it will fall within the range of the ADC on the MCU.
26
V
DD
V
DD
Capacitor
A capacitor is connected to this pin to filter the internal analog regulated supply.
This supply is derived from V
PWR
.
27
V
PWR
Positive Power Supply
12 V power applied to this pin will be converted to the regulated voltages needed
to operate the part. It is also converted to 5.0 V (V
CC
) and 8.5 V (V
DD
) to power
the MCU and external devices.
28
V
CC
5.0 V Regulator Output
This output pin requires a 47
μ
F capacitor and provides a regulated 5.0 V for the
MCU and for internal needs of the 33794.
29
AGND
Analog Ground
This pin is connected to the ground return of the analog circuitry. This ground
should be kept free of transient electrical noise like that from logic switching. Its
path to the electrical current return point should be kept separate from the return
for GND.
30
SHIELD
Shield Driver
This pin connects to cable shields to cancel cable capacitance.
32
GND
Ground
This pin and metal backing is the IC power return and thermal radiator/conductor.
35
TEST
Test Mode Control
This pin is normally connected to circuit ground. There are special operating
modes associated with this pin when it is not at ground.
SOICW-EP PIN FUNCTION DESCRIPTION (continued)
Pin
Pin Name
Formal Name
Definition
F
Freescale Semiconductor, Inc.
Go to: www.freescale.com
n
.