NCV7380 Просмотр технического описания (PDF) - ON Semiconductor

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NCV7380

LIN Transceiver

ON Semiconductor 

NCV7380

Recommendations for System Design

The goal of the LIN physical layer standard is to have a

universal definition of the LIN system for plug and play

solutions in LIN networks up to 20 kBd bus speeds.

In case of small and medium LIN networks, it’s

recommended to adjust the total network capacitance to at

least 4.0 nF for good EMC and EMI behavior. This can be

done by setting only the master node capacitance. The

slave node capacitance should have a unit load of typically

220 pF for good EMC/EMI behavior.

In large networks with long bus lines and the maximum

number of nodes, some system parameters can exceed the

defined limits and the LIN system designer must intervene.

The whole capacitance of a slave node is not only the unit

load capacitor itself. Additionally, there is the capacitance

of wires and connectors, and the internal capacitance of the

LIN transmitter. This internal capacitance is strongly

dependent on the technology of the IC manufacturer and

should be in the range of 30 pF to 150 pF. If the bus lines

have a total length of nearly 40m, the total bus capacitance

can exceed the LIN system limit of 10 nF.

A second parameter of concern is the integrated slave

termination resistor tolerance. If most of the slave nodes

have a slave termination resistance at the allowed

maximum of 60 kW, the total network resistance is more

than 700 W. Even if the total network capacitance is below

or equal to the maximum specified value of 10 nF, the

network time constant is higher than 7.0 ms.

This problem can be solved only by adjusting the master

termination resistor to the required maximum network time

constant of 5.0 ms (max).

NOTE: The NCV7380 meets the requirements for

implementation in RC−based slave nodes. The LIN

Protocol Specification requires the deviation of the slave

node clock to the master node clock after synchronization

must not differ by more than "2%.

Setting the network time constant is necessary in large

networks (primarily resistance) and also in small networks

(primarily capacitance).

VBUS

MIN/MAX SLOPE TIME CALCULATION

(In accordance to the LIN System Parameter Table)

100%

60%

60%

40%

40%

0%

Vdom

tsdom

tsrec

Figure 7. Slope Time and Slew Rate Calculation

(In accordance to LIN physical layer specification 1.3)

The slew rate of the bus voltage is measured between

40% and 60% of the output voltage swing (linear region).

The output voltage swing is the difference between

dominant and recessive bus voltage.

dVńdt + 0.2 * Vswingń(t40%−t60%)

The slope time is the extension of the slew rate tangent

until the upper and lower voltage swing limits:

tslope + 5 * (t40%−t60%)

The slope time of the recessive to dominant edge is directly

determined by the slew rate control of the transmitter:

tslope + VswingńdVńdt

The dominant to recessive edge is influenced from the

network time constant and the slew rate control, because it’s

a passive edge. In case of low battery voltages and high bus

loads the rising edge is only determined by the network. If the

rising edge slew rate exceeds the value of the dominant one,

the slew rate control determines the rising edge.

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