MC33794EKR2 Freescale, MC33794EKR2 Datasheet - Page 12

• Manufacturer Part Number: MC33794EKR2
• Manufacturer: Freescale

Specifications of MC33794EKR2

• Lead Free Status / RoHS Status: Compliant

RECT
offsetting the midpoint of the sine wave to zero volts and
inverting the waveform when it is below the midpoint. It is
important to avoid DC loading of the signal, which would
cause a shift in the midpoint voltage of the signal.
LPF
formed by an internal resistance and an external capacitance
attached to LP_CAP. The nominal value of the internal
resistance is 50 k
selected to provide filtering of noise while still allowing the
desired settling time for the detector output. A 10 nF
capacitor would allow 99% settling in less than 5.0 ms. In
practice, it is recommended you wait at least 1.5 ms after
selecting an electrode before reading LEVEL.
GAIN AND OFFSET
gain and offsets the result by a DC level. This results in an
output range that covers 1.0 V to 4.0 V for capacitive loading
of the field in the range of 10 pF to 100 pF. This allows higher
sensitivity for a digital-to-analog converter with a 0 V-to-5.0 V
input range.
ATTN
external use.
SHIELD_EN
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
SHIELD_EN is changed. If the SHIELD output is working and
properly connected, the capacitance of the coax will not be
cancelled when this terminal is asserted and the measured
capacitance will appear to change by approximately the
capacitance between the center conductor and the shield in
the coax.
LAMP CKT
terminal. When LAMP_CTRL is asserted, LAMP_OUT is
pulled to LAMP_GND. If one side of an indicator lamp or LED
size and proximity are to be determined. This is done by
placing electrodes in the area where the object will be. The
proximity of an object to an electrode can be determined by
the increase in effective capacitance as the object gets closer
to the electrode and modifies the electric field between the
12
MC33794
The rectifier circuit detects the level from MUX IN by
The rectified sine wave is filtered by a low pass function
This circuit multiplies the detected and filtered signal by a
This circuit passes the undetected signal to SIGNAL for
A logic low on this input disables the shield drive. The
This section controls the operation of the LAMP_OUT
The MC33794 is intended to be used where an object’s
Ω
. The value of the external capacitor is
APPLICATION INFORMATION
(with appropriate current setting resistor) is connected to a
positive voltage source and the other is connected to
LAMP_OUT, and LAMP_GND is connected to ground, the
lamp will light. This circuit provides current limiting to prevent
damage to itself in the case of a shorted lamp or during a
high-surge condition typical of an incandescent lamp
burnout.
if the lamp circuit is not used.
ISO-9141
communications. ISO_IN is data from the bus to the MCU
and ISO_OUT is data to drive onto the bus from the MCU.
POR/WD
timer. The
time after the V
minimum operating threshold. If V
any time,
time after V
also included, which will force a reset if V
maximum voltage. The watchdog function also can force
low if too long an interval is allowed to pass between positive
transitions on WD_IN.
INTERNAL V
regulated 5.0 V source, which is used internally and available
for other components requiring a regulated voltage source.
INTERNAL V
than 5.0 V. This is used by the device and some current is
available to operate op-amps and other devices. By having
this higher voltage available, some applications can avoid the
need for a rail-to-rail output amplifier and still achieve the 0 V-
to-5.0 V output for a digital-to-analog converter input.
V
allows a 0.0 V-to-5.0 V ADC to measure V
for V
CONTROL LOGIC
MUXes and some of the test modes
electrode and surrounding electrically common objects. The
shape and size of an object can be determined by using
multiple electrodes over an area and observing the
capacitance change on each of the electrodes. Those that
don’t change have nothing near them, and those that do
change have part of the object near them.
DD_MON
LAMP_GND should always be connected to ground even
This circuit connects to an ISO-9141 bus to allow remote
This circuit is a combined Power-ON Reset and watchdog
This circuit converts an unregulated voltage from VIN to a
This is a regulator for analog devices that require more
This contains the logic that decodes and controls the
DD
is 8.5 Volts.
is a divided output from internal V
RST
RST
CC
is pulled low again and held until the required
has returned high. An over voltage circuit is
CC
DD
CC
output is held low until a certain amount of
REG output (V
REGULATOR
REGULATOR
CC
CC
Freescale Semiconductor
) has remained above a
falls below the level at
CC
DD
DD
rises above a
. Normal value
REG, which
Sensors
RST