TCAN330 Datasheet, PDF (20/39 Pages) Texas Instruments – CAN Transceivers

TCAN330, TCAN332, TCAN334, TCAN337
TCAN330G, TCAN332G, TCAN334G, TCAN337G
SLLSEQ7A – DECEMBER 2015 – REVISED JANUARY 2016
www.ti.com
10.3.5 Fault Pin (TCAN337)
If one or more of the faults (TXD-Dominant Timeout, RXD dominant Timeout, Thermal Shutdown or
Undervoltage Lockout) occurs, the FAULT pin (open-drain) turns off, resulting in a high level when externally
pulled up to V_CC supply.
V_CC
P
FAULT
Input
FAULT
GND
TXD
DTO
RXD
DTO
Thermal
Shutdown
UV
Lockout
Figure 29. FAULT Pin Function Diagram and Application
10.3.6 Floating Pins
The device has internal pull ups and pull downs on critical terminals to place the device into known states if the
pin floats. See Table 1 for details on pin bias conditions.
PIN
TXD
STB
S
SHDN
PULL UP or PULL DOWN
Pull up
Pull down
Pull down
Pull down
Table 2. Pin Bias
COMMENT
Weakly biases TXD toward recessive to prevent bus blockage or TXD DTO
triggering.
Weakly biases STB terminal towards normal mode.
Weakly biases S terminal towards normal mode.
Weakly biases SHDN terminal towards normal mode.
The internal bias should not be relied on by design, especially in noisy environments, but should be considered a
fall back protection. Special care needs to be taken when the device is used with MCUs using open drain
outputs. TXD is weakly internally pulled up. The TXD pull up strength and CAN bit timing require special
consideration when this device is used with an open drain TXD output on the microprocessor's CAN controller.
An adequate external pull up resistor must be used to ensure that the TXD output of the microprocessor
maintains adequate bit timing input to the CAN transceiver.
10.3.7 CAN Bus Short Circuit Current Limiting
The device has several protection features that limit the short circuit current when a CAN bus line is shorted.
These include CAN driver current limiting (dominant and recessive). The device has TXD dominant time out
which prevents permanently having the higher short circuit current of dominant state in case of a system fault.
During CAN communication the bus switches between dominant and recessive states, thus the short circuit
current may be viewed either as the current during each bus state or as a DC average current. For system
current and power considerations in the termination resistors and common mode choke ratings the average short
circuit current should be used. The percentage dominant is limited by the TXD dominant time out and CAN
protocol which has forced state changes and recessive bits such as bit stuffing, control fields, and interframe
space. These ensure there is a minimum recessive amount of time on the bus even if the data field contains a
high percentage of dominant bits.
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