In the design of CAN node, we the news report for bus line is more normally reliable, increase all sorts of parts of an apparatus for CAN interface, but be not all application actually to need, defend too much raise cost not only, and the parasitism parameter of parts of an apparatus affects signal quality necessarily. The article will introduce simply in all the function that modular inductance uses at bus line.

 

 

 

We see in applying actually a lot of CAN products can be used in all modular inductance, but cannot see it have clear improvement to which index however in groovy test, affect undee quality instead. A lot of engineers to be ready for any eventuality, ensure reliable, can add comprehensive periphery circuitry to CAN. CAN chip has had fight very well electrostatic, ability of transient state voltage, some are sent and receive implement itself also has very good EMC property, we are in application can defend according to designing requirement one by one to increase, the periphery such as filter wave. Should add to otherwise of CAN bus line in all modular inductance, we are main from electromagnetism compatible respect considers.

 

 

 

1, in all modular inductance

 

 

 

Introduce first in all modular interference, graph 1, graph 2 gave out respectively wrong standard and in all modular interference reachs his to transmit method. The driver in the graph and receiver divide signal to transmit for difference, similar CAN bus line. The interference that need a standard arises between two transmission line, in all modular interference arises at the same time in two lines, its electromotive force is it is reference with the ground.

 

 

Graph interference of 1 wrong standard reachs transmission way

 

Graph 2 in all modular interference reachs transmission way

 

In all modular inductance is the fluctuation in annulus of a magnetism on two half annulus, circle respectively make identical v/LIT all over the ground number but circle to contrary coil. In all modular interference is identical, the lines of force that forms in magnetism annulus so mutual overlay, inductance block the Chinese People’s Anti-Japanese Military and Political College has the effect that disturbs damply thereby. The lines of force that forms in magnetism annulus to needing modular signal offsets each other, do not have inhibition, only coil resistor and very little leakage sense have appreciably to affect to needing modular signal. In all modular inductance is a two-way filter substantially, on one hand filter divides line to go up in all modular signal interference, restrain line itself not to give out electromagnetism interference outwards on the other hand. Graph 2 medium interference signal criterion can well by in all modular inductance is restrained, and the signal that need branch does not have an influence almost.

 

 

CAN is sent and receive implement in-house CANH, CANL is a source respectively, open leakage to output a form, drive circuit is shown 3 times like the graph. This kind of means can make bus line realizes the drive of dominance n easily, and recessive n comes true through terminal resistor discharge.

 

 

Graph 3 CAN is sent and receive implement drive circuit

 

The poor cent with inherent bus line transmits a form to make CAN to in all modular interference has control capacity very well, if the graph is shown 4 times, decrease through photograph of CANH, CANL can eliminate well come from external in all modular interference, but CANH, CANL is not ideal semmetry, rise quickly jump change along, these all can bring EMC issue. We see bus line weaveform through oscillograph very perfect, the test is electrostatic, EFT, surge, conduct annoy fight faze to all be not had unusual. But test conducted emission, cannot satisfy be restricted to be worth a requirement, the bus line that looks very normal is in actually outwards however send conducted interference.

 

Graph 4 CAN transmits weaveform

 

 

To the EMC problem of CAN interface, besides choose better performance, the CAN that the symbol asks sends and receive chip, another kind of simple method increases periphery to CAN interface namely, in all modular inductance is a kind of very good choice. In standard of CISPR 25 of existing car electron, annoy to conducting be restricted to be worth have very firm demand. A lot of CAN are sent and receive implement all can be restricted to be worth more than. If pursue 5 increase to limit a test according to car compasses respectively and do not add in all the CAN interface of modular inductance is conducted annoy, in all modular inductance value is 51μH, can see in each frequency paragraph next is opposite noise improvement is relatively clear, the test still has amount of very big abundant as a result.

 

 

Graph 5 conduct annoy a test

 

In all modular inductance is conducted to reducing annoy have apparent effect, can help us adopt test requirement quickly, contented and existing car uses a requirement, but bus line increases in all modular inductance also can bring two issues: Resonance and transient state voltage. In all modular inductance can have parasitism inductance inevitably, dc block, consider check the number of bus line division, the element such as communication distance, can cause resonance, affect quality of bus line signal, if pursue 6, green weaveform is increase in all the bus line of modular inductance is undee, signal drops the edge already had apparent resonance. Additional, in all amount of modular inductance feeling is larger, and direct division is in send and receive implement interface, short circuit appears in applying actually, heat is inserted unplug wait for condition to be able to make in all two end produce modular inductance transient state high pressure, serious when can direct damage is sent and receive implement.

 

 

Graph 6 increase in all the CAN of modular inductance is undee

 

 

 

 

In all the actor weakness that modular inductance uses at bus line is relatively apparent, it is OK filter eliminates line in all modular electromagnetism interference, attenuation difference distributes signal high frequency part, restrain the electromagnetism interference that CAN interface oneself gives out outwards, in conduct annoy a respect to have improve function well, but the resonance that application still wants to consider its to bring and transient state voltage, these is in Sunday run, to bus line signal quality is adverse in much node communication, apply pair of conducted emission to general industry and do not have strict requirement, can not increase accordingly in all modular inductance.

ZLG sends far electron to be based on old bus line to defend the design is accumulated rolled out tall defend grade keeps apart module ——CTM1051(A)HP series. This series accords with international ISO11898-2 standard, electrostatic defend grade can amount to osculatory ±8kV, air discharge ±15kV, surge defends can amount to ±4kV to keep apart CAN solution, specific following graphs are shown 7 times, can apply to all sorts of harsh industrial spot environments. Application is handy, plug and Play, applied principle graph pursues as follows 8 are shown.

 

 

The EMC function of graph 7 CTM1051(A)HP

 

Graph graph of 8 application principle