Datasheet


SGLS356 − MAY 2006
22
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APPLICATION INFORMATION
standby mode (listen only mode) of the SN65HVD230M
If a logic high (> 0.75 V
CC
) is applied to R
S
(pin 8) in Figure 29 and Figure 31, the circuit of the SN65HVD230M
enters a low-current, listen only standby mode during which the driver is switched off and the receiver remains
active. In this listen only state, the transceiver is completely passive to the bus. It makes no difference if a slope
control resistor is in place as shown in Figure 31. The DSP can reverse this low-power standby mode when the
rising edge of a dominant state (bus differential voltage > 900 mV typical) occurs on the bus. The DSP, sensing
bus activity, reactivates the driver circuit by placing a logic low (< 1.2 V) on R
S
(pin 8).
loop propagation delay
Transceiver loop delay is a measure of the overall device propagation delay, consisting of the delay from the
driver input to the differential outputs, plus the delay from the receiver inputs to its output.
The loop delay of the transceiver displayed in Figure 34 increases accordingly when slope control is being used.
This increased loop delay means that the total bus length must be reduced to meet the CAN bit-timing
requirements of the overall system. The loop delay becomes ≈100 ns when employing slope control with a
10-kΩ resistor, and ≈500 ns with a 100-kΩ resistor. Therefore, considering that the rule-of-thumb propagation
delay of typical bus cable is 5 ns/m, slope control with the 100-kΩ resistor decreases the allowable bus length
by the difference between the 500-ns max loop delay and the loop delay with no slope control, 70.7 ns. This
equates to (500–70.7 ns)/5 ns, or approximately 86 m less bus length. This slew-rate/bus length trade-off to
reduce electromagnetic interference to adjoining circuits from the bus can also be solved with a high-quality
shielded bus cable.