TH8053 View Datasheet(PDF) - Melexis Microelectronic Systems
Part Name
Description
MFG CO.
TH8053 Datasheet PDF : 14 Pages
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TH8053
Fault Tolerant Low Speed CAN Transceiver
Functional Description (continued)
The signal coming from the differential CAN bus is fed to
a filter stage to inhibit high frequencies that interfere the
bus line from disturbing the evaluation of the incoming
bus data. The cut-off frequency of the filters has to be re-
garded as a trade-off between RF-suppression and
propagation delay.
The failure detection circuit determines whether one of
the failures described in Table 1, “CAN bus failures, ex-
ists and indicates a present error as an active LOW at
the NERR output. Furthermore the information of the
kind of failure is given to the failure management block
which takes the appropriate measures to ensure trans-
mission and reception of data. This includes the control
of the correct termination of the CAN bus lines as well as
the choice of the right derivation of the receiver signal
(output to the RXD-pin) from the CANH and CANL in-
puts. The failure management also contains the possibil-
ity to disable one of the driver stages (e.g. in the case of
failure 6 the high side driver and the RTH termination are
disabled to reduce current consumption). During any kind
of single-wire data transfer RF-radiation and RF-
sensitivity are increased.
The failure detection consists of two detection circuits,
one being active in the normal operation mode and the
other one working in the standby and sleep modes. Re-
covery of the failures is done with a certain time-out that
depends on the failure. A wake-up function that detects
incoming dominant signals from the bus is also included.
A wake-up command can also be generated by changing
the logical voltage level at the WAKE-pin. The mode the
TH8053 is running within and whether the INH-pin dis-
ables an external voltage regulator can be controlled by
the EN- and STB-pins as shown in Table 3, “Mode Con-
trol, on page 4 and detailed described in “Operation
Modes” on page 4
Another feature implied in this can transceiver device is
Table 1 - CAN bus failures
(Definition in accordance with ISO 11519-2)
Nr. Failure description
Condition
1 CANL wire interrupted
2 CANH wire interrupted
3 CANL short-circuited to battery
supply voltage
3a
4 CANH short-circuited to ground
5 CANL short-circuited to ground
6
CANH short-circuited to battery
supply voltage
6a
7 CANH short-circuited to CANL
VBAT>7.2
V1.8V<VBAT<7.2V
VBAT>7.2 V
1.8V<VBAT<7.2V
the time-out circuit at the TXD-Input that prevents occu-
pation of the CAN bus by a long-term dominant signal
sent from the CAN controller. If no failure occurs the
TXD-signal coming from the CAN controller is fed to the
driver stage which includes a limitation of slopes to re-
duce RF-interference caused by radiation on the CAN
bus.
To prevent the chip from a thermal breakdown a tem-
perature protection circuit shuts down the driver stages
which represent the biggest part of the whole power con-
sumption. All other parts remain active thus a reception
of data is still possible. After cooling down and reaching
the low temperature level the transmitter will be enabled
again.
Error Management
Depending on the occurring error appropriate measures
have to be taken to ensure data transmission and recep-
tion. Table 2, “Error Management”, lists the means to
achieve this target in the normal operation mode. The
comparator signal that determines the value of RXD is
given in the second column, the third and fourth ones
contain the information whether either one of the termi-
nations RTH or RTL is switched off to reduce the current
flowing in the termination resistances. The last two col-
umns display if one of the transmitter drivers is deacti-
vated.
If an interrupt of the CANH or CANL wire between two
ECUs is detected (failures 1 and 2) there is no need to
disable the corresponding high or low side driver be-
cause differential transmission towards other ECUs may
still be useful.
Table 2 - Error Management
Errors 1 and 3a as well as errors 2 and 4 can’t be distinguished
by the receiver.
Error
Output
to RXD
1
D
2
D
3
H
3a
D
4
D
5
H
6
L
6a
L
7
H
Termination1
RTH
on
on
on
on
on
on
off
off
on
RTL
on
on
off
on
on
off
on
on
off
Driver
CANH
on
on
on
on
on
on
on
on
on
CANL
on
on
off2
on
on
off
on
on
off
______________________________
1 If the termination is switched off, a current of 75µA is supplied at the RTH -or RTL-pin.
2 Low side driver is switched off after two unsuccessful attempts of reaching dominant level.
Datasheet Rev 1.2 Nov 2000
Page 3
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