FS6407 datasheet(58/111 Pages) NXP

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NXP Semiconductors

FS6407/FS6408

Figure 43. TXD dominant timeout detection

6.8.2.2

RXD permanent recessive

If RXD is detected high for seven consecutive receive/dominant cycles, the CAN drivers and receiver are disabled, and the CAN bus

returns to recessive state. This prevent a CAN protocol controller to start CAN message on TXD pin, while RXD is shorted to a recessive

level, and seen from a CAN controller as a bus idle state.

The CAN_mode MSB bit is set to 0 and the flag RXD_recessive is reported in the Diag CAN1 register. The device recovers from this error

detection after setting the CAN_mode to Normal operation. The RXD failure detection is operating when the CAN transceiver is in Normal

mode and Listen Only mode.

6.8.2.3

CAN bus short-circuits

CANL short to GND and CANL short to battery are detected and reported to the device main logic. The CAN driver and receiver are not

be disabled. CANH short to GND and CANH short to battery are detected and reported to the device main logic. The CAN driver and

receiver are not be disabled. The CANH and CANL failure detection is operating when the CAN transceiver is in Normal mode.

If the CAN bus is dominant for a time longer than tDOM, due for instance to an external short-circuit from another CAN node, the flag

CAN_dominant is reported in the Diag CAN1 register. This failure does not disable the bus driver. The CAN bus dominant failure detection

is operating when the CAN transceiver is in Normal mode and Listen Only mode.

6.8.2.4

CAN current limitation

The current flowing in and out of the CANH and CANL driver is limited to 100 mA, in case of a short-circuit (parameters ICANL-SK and

ICANH-SC).

6.8.2.5

CAN overtemperature

If the driver temperature exceeds the TSD (TOT), the CAN drivers are disabled, and the CAN bus returns to recessive state. The CAN

receiver continues to operate. The CAN_mode MSB bit is set to 0 and the flag CAN_OT is reported in the Diag CAN register.

An hysteresis is implemented in this protection feature. The device overtemperature and recovery conditions are shown in Figure 44. The

CAN drivers remain disabled until the temperature has fallen below the OT threshold minus hysteresis. The device recovers from this error

detection after setting the CAN_mode to Normal operation and when a high level is detected on TXD.

TXD

high

dominant

recessive

BUS

TDOUT

dominant

low

RXD

high

low

TXD dom time out expired

recovery condition: TXD high

TDOUT

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