Can interface circuit

The CAN-bus should be terminated at each ends with a ohm resistor. But why make things simple? In split termination, two 60 ohm resistors are used in series, totalling ohms. The electrical node between the two resistors is connected to ground through a capacitor, usually of 4. The value of the capacitor has been calculated to obtain a -3db cut-off frequency at the fundamental frequency of the network.

Assuming the worst-case scenario, when the network is transmitting a sequence of alternating bits the signal will be a square wave of frequency kHz, or equal to half the baud rate.

We know the resistance at 60 ohms, we can thus calculate the capacitor. Hence, 4. If your system is not subject to heavy ESD, the included protection in the transceiver IC could be everything that is needed. TVS Transient Voltage Suppressor diodes are a common choice due to their low equivalent parallel capacitance. Other over-voltage protection devices, such as MOVs, often have a high parasitic capacitance that can limit the bus data rates, especially for busses with many nodes.

As for the transceiver, I placed the model with one click from Altium libraries using the Manufacturer Part Search panel, without having to draw the schematic symbol and footprint. If your circuit were without protection, all the EMI current would go straight into your transceiver from your connector, and then back through the ground plane. All your protection components should be as close as possible to that path to avoid increasing the loop area. In our case, TVS diodes have to deal with high-speed high-current events.

As fast impulses are rich in high-frequency components, if left unchecked to roam into our boards, they will couple with every available trace and disrupt operation. In our example PCB, there is still room for improvement. The capacitors C5 and C6 could be rotated degrees as well and moved a tiny bit to the right.

Your TVS diodes should discharge the impulses directly to the ground plane, connected to the cable shield if available through a low-inductance connection. The via must be tented; otherwise, the solder paste will flow inside, and the pad would not be adequately wetted.

You can find documentation on Altium Designer via properties here. Now what? The first step is designing your circuit in a single schematic document, using ports for input and outputs, similarly to what you would do for hierarchical design. Once your folder has been created, all users within your organization will have access to it, and you can proceed to upload the schematic sheet.

The same resistance, however, contributes to load the network, reducing the number of nodes, decreasing the final nominal impedance of the bus, and reducing the maximum speed. It would help if you always kept in mind, however, that these devices may increase your equivalent bus capacitance and lower your data-rates and increase current consumption.

Standard mode chokes are the most common type of filter used on CAN-Bus, and they work great, but they have some drawbacks you should consider. Common-mode chokes can create resonances with the parasitic capacitance of the CAN-bus bus, leading to increased noise in a few specific frequency bands.

This effect can make the EMI properties of CAN-bus devices unpredictable, since the inductance in common-mode chokes is rarely specified precisely, and the parasitic capacitance can vary wildly with cable lengths. If an unshielded cable is used, the capacitance can vary depending on the proximity of the cable to grounded metal surfaces.

As we all know, common-mode inductors behave as inductors in common mode. Some fault conditions, such as a short to power or ground, can cause high transient common-mode currents. In some cases, the overvoltage created by the inductance of the common mode choke can damage the CAN-bus transceivers. These over-voltages can be rather nasty to debug, as they are created after the overvoltage protection, which is typically placed at the edge of the board.

Each written message must have an ID and length. In the second snippet of code shown, we write data to each byte, then send the message The ID and length parameters are defined earlier in the code. When connecting multiple CAN nodes, careful attention should be paid to the length of cables. The two farthest nodes can be up to 40m apart from each other. Middle nodes connecting to the bus should be within 50cm of the main bus lines. And if it's your first order, get 10 boards for the same price!

Just upload your gerbers and get an instant quote! Submit your order and your boards will be reviewed for production within the hour. Once you pay, you can expect your high quality boards in as soon as three days! We placed our order on Friday and got the boards on Wednesday! The bus is in the dominant state if the differential voltage is greater than 0.

The circuit shown in Figure 2 uses a square wave signal from a function generator to provide adjustable CAN signals to a transceiver. The AD high speed differential amplifier was chosen for its wide bandwidth and low distortion.

A dc level shifter at the output enables the differential level of the output signals to be adjusted while maintaining their peak-to-peak levels. The amplitude and frequency are adjusted via the signal generator.

Operating from a single 5-V supply, the circuit is configured as a unity-gain single-ended-to-differential amplifier with common mode set at midsupply.