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CAN transceiver

Extended data-rate of 4 Mbit/s

Linear Technology’s LTC2875 is a high-speed, low power CAN transceiver. It operates on 3,3-V or 5-V supplies. It features ±60 V overvoltage fault protection on the data transmission lines during all modes of operation, including power-down.

CAN link with large ground loop voltage (Photo: Linear Technology)

THE MAXIMUM DATA-RATE HAS BEEN EXTENDED to 4 Mbit/s to support high speed protocols based on the CAN physical layer. Enhanced ESD protection allows these parts to withstand ±25 kV HBM on the transceiver interface pins without latch-up or damage.

A ±36-V input common mode range and high common mode rejection on the CAN receiver provides tolerance to large ground loop voltages. A CAN driver with active symmetry control maintains control of the common mode voltage for electromagnetic emission. The variable slew rate and split termination support allow additional EME reduction.

Transmitting at 4 Mbit/s from a 3,3-V supply (Photo: Linear Technology)

When operating from a 5-V supply, the LTC2875 adheres to the ISO 11898-2 CAN standard by maintaining drive levels that are symmetric around VCC/2 = 2,5 V. An internal common mode reference of VCC/2 is buffered to supply the termination of the receiver input resistors. A second buffer with a high voltage tolerant output supplies VCC/2 to the Split output.

When operating from a 3,3-V supply, the 2,5-V nominal common mode voltage specified in the ISO 11898-2 standard is too close to the 3,3-V supply to provide symmetric drive levels while maintaining the necessary differential output voltage. To maintain driver symmetry, the common mode reference voltage is lowered during 3,3-V operation. The typical output common mode voltage is 1,95 V in the domi-nant state. The internal common mode reference is set to VCC/2 + 0,3 V = 1,95 V to match the dominant state output common mode voltage. This reference is independently buffered to supply the termination of the receiver input resistors and the Split voltage output.

As the LTC2875 operates over a wide common mode range, this shift of –0,55 V in the common mode when operating from 3,3 V does not degrade data transmission or reception. An LTC2875 operating at 3,3 V may share a bus with other CAN transceivers operating at 5 V. However, the electromagnetic emissions may be larger if transceivers powered by different voltages share a bus, due to the fluctuation in the common mode voltage from 1,95 V (when an LTC2875 on a 3,3-V supply is dominant) to 2,5 V (when a CAN transceiver on a 5-V supply is dominant).