MC33388 Datasheet, PDF (25/28 Pages) Motorola, Inc – Fault Tolerant CAN Interface

MC33388
PIN FUNCTION DESCRIPTION
VBAT (input) : This is the supply line of the device. It can
be directly connected to the battery line, can operate up to
27VDC and sustains up to 40V during load dump condition.
The supply current is dependant upon the device operation
mode. In low power mode, it is as low as 12uA typical. A
battery fail flag circuitry is associated to this pin.
The Vbat pin must be protected by external component
against reverse battery and negative transient voltages.
VDD (input) : 5V input supply voltage for the device. In
normal mode, the current is up to 5mA typical and do not
exceed few uA in Vbat standby mode. An under voltage
function is associated to Vdd and resets the device to Vbat
standby mode when Vdd falls below 3V.
CANH : Bus output driver pin. CANH is a high side switch
structure connected to VDD supply. In recessive state, the
high side switch is off and bus CANH line is biassed through
the Rth pin circuitry and external Rth resistor. In dominant
state, high side switch is on and CANH line is switched to
VDD. Output voltage is above 3.6V. CANH output is protected
against short-circuit to ground, by internal current limitation. A
thermal shutdown with hysteresis switches off CANH driver if
temperature rises above 150°C. CANH is also protected
against short-circuit to higher voltage, such as VBAT by an
internal serial diode in series with the switching component.
CANH has a pull down current source, typically 75uA, which
can be activated under some fault condition.
Rth : Connection to the CANH bus terminal resistors. Rth
output structure is a low side switch, turned on under normal
condition and automatically desactivated under some fault
condition. In the application, an external resistor is con-
nected between Rth and CANH pins. In recessive state
when CANH driver is off, CANH line is tied to ground through
the external Rth resistor.
CANL : Bus output driver pin. CANL is a low side switch
structure to the ground. In recessive state, the low side switch
is off, and bus CANL line is biassed through the Rtl circuitry
and external Rtl resistor. In dominant state, low side switch is
on and CANL line is switched to ground. Output voltage is
below 1.4V. CANL output is protected against short-circuit to
VBAT, by internal current limitation. A thermal shutdown with
hysteresis is integrated and switches off CANL driver if
temperature rises above 150°C. CANL is protected against
negative voltage, by an internal serial diode in series with the
switching component. CANL has a pull up current source,
typically 75uA, activated under some fault condition.
Rtl : Connection to the CANL bus terminal resistors. Rtl
output structure is a low side switch, turned on under normal
condition and automatically desactivated under some fault
condition. In the application, an external resistor is connected
between Rtl and CANL pins. In recessive state when CANL
driver is off, CANL line is tied to VDD through external Rtl
resistor.
In VBAT Standby and Sleep modes, Rtl pin is connected
to the VBAT line through an internal switch and a 12.5kΩ
resistor. This means that in these modes CANL bus line is
biassed to VBAT. Wake up from these modes are detected by
CANL line going from VBAT level to CANL wake up threshold
level.
STB and EN : Input pins used to configure the device into
desired mode. These pins are CMOS compatible and are
connected to the microcontroller of the application.
INH : This is an output of the MC33388 used to control an
external voltage regulator having an inhibit input. INH is a high
side switch structure, active when the MC33388 is in normal,
Receive only or Standby VBAT modes. INH is switched off in
Sleep mode to switch off the voltage regulator of the
application. INH has no pull down structure.
WAKE : This is a high voltage input used to wake up the
device from Sleep and VBAT Standby modes. Wake is
usually connected to an external switch in the application. The
typical wake thresholds are Vbat/2.
Wake pin has special design structure and allows wake up
from both high to low or low to high transitions. When entering
into the Sleep or VBAT Standby mode, the MC33388
monitors the state of the wake pin and stores it as reference
state. The opposite state of this reference state will be the
wake up event used by the device to enter again into normal
mode.
An internal filter is implemented, with 8 to 38 µs filtering
time delay. Wake pin input structure exhibits a high
impedance, with extremely low input current. A serial resistor
should be inserted in order to limit the input current mainly
during transient pulses.
CAUTION : The Wake pin should not be left open. If wake
up function is not used, wake should be connected to GND to
avoid false wake up.
TX : Transmitter input pin to control bus state. It is CMOS
compatible and usually directly connected to the TX output of
a microcontroller. When TX is at high state, CANH and CANL
are in recessive state. When TX is low, CANL and CANH are
in dominant state. Special fault handling is provided to this
input, in order to detect permanent dominant state (TX low)
which would result of CAN bus permanently lock in dominant
state and do not allow communication. In case where TX is
low for more than 2ms typical, the device automatically
switches the bus lines to recessive. TX has an internal pull up
resistor to VDD.
RX : Output receiver connection to the microcontroller. It
reports the bus state to the RX input pin of the microcontroller.
RX is high when bus is recessive and low in dominant state. In
sleep and standby Vbat modes, RX reports wake up events.
NERR : Error output pin which reports errors encountered
by the device. When NERR is high, no error is reported, when
NERR is low an error has been detected. In Standby VBAT
mode NERR reports a wake up event. In receive only mode,
NERR reports VBAT power on flag.
Table 3 • Truth Table of RX, TX CAN Bus States
TX
RX Bus States
Low Low Dominant
High High Recessive
Comment
High Low Dominant
Bus Driven By Other Node
MC33388
MOTOROLA
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