11.3.2 Differential Signal

CAN is a differential bus where complementary signals are sent over two wires and the voltage difference between the two wires defines the logical state of the bus. The differential CAN receiver monitors this voltage difference and outputs the bus state with a single ended logic level output signal.

Figure 39. Typical Differential Output Waveform

The CAN driver creates the differential voltage between CANH and CANL in the dominant state. The dominant differential output of the TCAN33x is greater than 1.5 V and less than 3 V across a 60-Ω load as defined by the ISO11898 standard. These are the same limiting values for 5 V supplied CAN transceivers. The bus termination resistors drive the recessive bus state and not the CAN driver.

A CAN receiver is required to output a recessive state when less than 500 mV of differential voltage exists on the bus, and a dominant state when more than 900 mV of differential voltage exists on the bus. The CAN receiver must do this with common-mode input voltages from –2 V to 7 V. The TCAN33x family receivers meet these same input specifications as 5 V supplied receivers.