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TJA1041AT Datasheet(PDF) 10 Page - NXP Semiconductors |
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TJA1041AT Datasheet(HTML) 10 Page - NXP Semiconductors |
10 / 24 page 2004 Feb 20 10 Philips Semiconductors Product specification High speed CAN transceiver TJA1041A The tdom(TXD) timer defines the minimum possible bit rate of 40 kbit/s. The transmitter remains disabled until the local failure flag is cleared. RXD RECESSIVE CLAMPING DETECTION An RXD pin clamped to HIGH level will prevent the controller connected to this pin from recognizing a bus dominant state. So the controller can start messages at any time, which is likely to disturb all bus communication. RXD recessive clamping detection prevents this effect by disabling the transmitter when the bus is in dominant state without RXD reflecting this. The transmitter remains disabled until the local failure flag is cleared. TXD-TO-RXD SHORT-CIRCUIT DETECTION A short-circuit between pins RXD and TXD would keep the bus in a permanent dominant state once the bus is driven dominant, because the low-side driver of RXD is typically stronger than the high-side driver of the controller connected to TXD. The TXD-to-RXD short-circuit detection prevents such a network lock-up by disabling the transmitter. The transmitter remains disabled until the local failure flag is cleared. BUS DOMINANT CLAMPING DETECTION A CAN bus short circuit (to VBAT,VCC or GND) or a failure in one of the other network nodes could result in a differential voltage on the bus high enough to represent a bus dominant state. Because a node will not start transmission if the bus is dominant, the normal bus failure detection will not detect this failure, but the bus dominant clamping detection will. The local failure flag is set if the dominant state on the bus persists for longer than tdom(bus). By checking this flag, the controller can determine if a clamped bus is blocking network communication. There is no need to disable the transmitter. Note that the local failure flag does not retain a bus dominant clamping failure, and is released as soon as the bus returns to recessive state. OVER-TEMPERATURE DETECTION To protect the output drivers of the transceiver against overheating, the transmitter will be disabled if the virtual junction temperature exceeds the shutdown junction temperature Tj(sd). The transmitter remains disabled until the local failure flag is cleared. Recessive bus voltage stabilization In recessive state the output impedance of transceivers is relatively high. In a partially powered network (supply voltage is off in some of the nodes) any deactivated transceiver with a significant leakage current is likely to load the recessive bus to ground. This will cause a common-mode voltage step each time transmission starts, resulting in increased ElectroMagnetic Emission (EME). Using pin SPLIT of the TJA1041A in combination with split termination (see Fig.5) will reduce this step effect. In normal mode and pwon/listen-only mode pin SPLIT provides a stabilized 0.5VCC DC voltage. In standby mode, go-to-sleep command mode and sleep mode pin SPLIT is set floating. I/O level adapter The TJA1041A is equipped with a built-in I/O-level adapter. By using the supply voltage of the controller (to be supplied at pin VI/O) the level adapter ratio-metrically scales the I/O-levels of the transceiver. For pins TXD, STB and EN the digital input threshold level is adjusted, and for pins RXD and ERR the HIGH-level output voltage is adjusted. This allows the transceiver to be directly interfaced with controllers on supply voltages between 2.8 V and 5.25 V, without the need for glue logic. Pin WAKE Pin WAKE of the TJA1041A allows local wake-up triggering by a LOW to HIGH state change as well as a HIGH to LOW state change. This gives maximum flexibility when designing a local wake-up circuit. To keep current consumption at a minimum, after a twake delay the internal bias voltage of pin WAKE will follow the logic state of this pin. A HIGH level on pin WAKE is followed by an internal pull-up to VBAT. A LOW level on pin WAKE is followed by an internal pull-down towards GND. To ensure EMI performance in applications not using local wake-up it is recommended to connect pin WAKE to pin VBAT or to pin GND. |
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