Place the protection and filtering circuitry close to the bus connector, J1, to prevent transients, ESD, and noise from propagating onto the board. This layout example shows an optional transient voltage suppression (TVS) diode, D1, which may be implemented if the system-level requirements exceed the specified rating of the transceiver. This example also shows optional bus filter capacitors C4 and C5.
Design the bus protection components in the direction of the signal path. Do not force the transient current to divert from the signal path to reach the protection device.
Decoupling capacitors should be placed as close as possible to the supply pins VCC and VIO of transceiver.
Use at least two vias for supply and ground connections of bypass capacitors and protection devices to minimize trace and via inductance.
Note:
High frequency current follows the path of least impedance and not the path of least resistance.
This layout example shows how split termination could be implemented on the CAN node. The termination is split into two resistors, R6 and R7, with the center or split tap of the termination connected to ground via capacitor C3. Split termination provides common mode filtering for the bus. See Section 8.2.1.1, Section 7.3.4, and 2 for information on termination concepts and power ratings needed for the termination resistor(s).
To limit current,
digital lines series resistors can be used. Examples are R2, R3 and R4.
Pin 1 is shown for the TXD input of the device
with R1 as an optional pull-up resistor. If an open drain host controller is
used, making sure the bit timing into the device is met is mandatory.
Pin 8 is shown with R4 assuming the mode pin STB, is used. If the device is used in normal mode only, R4 is not needed and the pads of C4 could be used for the pull down resistor R5 to GND.