TCAN330_16 Datasheet, PDF (19/40 Pages) Texas Instruments – 3.3-V CAN Transceivers with CAN FD (Flexible Data Rate)

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TCAN330, TCAN332, TCAN334, TCAN337
TCAN330G, TCAN332G, TCAN334G, TCAN337G
SLLSEQ7D – DECEMBER 2015 – REVISED APRIL 2016
10.3 Feature Description
10.3.1 TXD Dominant Timeout (TXD DTO)
During normal mode (the only mode where the CAN driver is active), the TXD DTO circuit prevents the
transceiver from blocking network communication in the event of a hardware or software failure where TXD is
held dominant longer than the timeout period t_{TXD_DTO}. The DTO circuit timer starts on a falling edge on TXD.
The DTO circuit disables the CAN bus driver if no rising edge is seen before the timeout period expires. This
frees the bus for communication between other nodes on the network. The CAN driver is re-activated when a
recessive signal is seen on TXD pin, thus clearing the TXD DTO condition. The receiver and RXD pin still reflect
the CAN bus, and the bus pins are biased to recessive level during a TXD dominant timeout.
10.3.2 RXD Dominant Timeout (RXD DTO)
All devices have a RXD DTO circuit that prevents a bus stuck dominant fault from permanently driving the RXD
output dominant (low) when the bus is held dominant longer than the timeout period t_{RXD_DTO}. The RXD DTO
timer starts on a falling edge on RXD (bus going dominant). If no rising edge (bus returning recessive) is seen
before the timeout constant of the circuit expires (t_{RXD_DTO}), the RXD pin returns high (recessive). The RXD
output is re-activated to mirror the bus receiver output when a recessive signal is seen on the bus, clearing the
RXD dominant timeout. The CAN bus pins are biased to the recessive level during a RXD DTO.
10.3.3 Thermal Shutdown
If the junction temperature of the device exceeds the thermal shutdown threshold, the device turns off the CAN
driver circuits thus blocking the TXD-to-bus transmission path. The shutdown condition is cleared when the
junction temperature of the device drops below the thermal shutdown temperature of the device. If the fault
condition that caused the thermal shutdown is still present, the temperature may rise again and the device will
enter thermal shut down again. Prolonged operation with thermal shutdown conditions may affect device
reliability. The thermal shutdown circuit includes hysteresis to avoid oscillation of the driver output.
During thermal shutdown the CAN bus drivers are turned off, thus no transmission is possible from TXD to the
bus. The CAN bus pins are biased to recessive level during a thermal shutdown and the receiver to RXD path
remains operational.
10.3.4 Undervoltage Lockout and Unpowered Device
The V_CC supply terminal has under voltage detection which will place the device in protected mode if the supply
drops below the UVLO threshold. This protects the bus during an under voltage event on V_CC by placing the bus
into a high impedance biased to ground state and the RXD terminal into a tri-stated (high impedance) state.
During undervoltage the device does not pass any signals from the bus. If the device is in normal mode and V_CC
supply is lost the device will transition to a protected mode.
The device is designed to be an "ideal passive" or “no load” to the CAN bus if the device is unpowered. The bus
terminals (CANH, CANL) have low leakage currents when the device is unpowered, so the device does not load
the bus. This is critical if some nodes of the network are unpowered while the rest of the of network remains
operational. Logic pins also have low leakage currents when the device is unpowered, so the device does not
load other circuits which may remain powered.
V_CC
GOOD
BAD
UNPOWERED
Table 1. Undervoltage Protection 3.3-V Single Supply Devices
DEVICE STATE
Operational
Protected
Unpowered
BUS
Per Operating Mode
Common mode bias to GND
High Impedance (no load)
RXD
Per Operating Mode
High Impedance
High Impedance
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