SN65HVD230
SN65HVD231
SN65HVD232
SLOS346G – MARCH 2001 – REVISED JUNE 2002
APPLICATION INFORMATION
standby mode (listen only mode) of the HVD230
If a logic high (> 0.75 V ) is applied to R (pin 8) in Figures 30 and 32, the circuit of the SN65HVD230 enters
CC
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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 32. 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 (pin 8).
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the babbling idiot protection of the HVD230
Occasionally, a runaway CAN controller unintentionally sends messages that completely tie up the bus (what
is referred to in CAN jargon as a babbling idiot). When this occurs, the DSP can engage the listen-only standby
mode to disengage the driver and release the bus, even when access to the CAN controller has been lost. When
the driver circuit is deactivated, its outputs default to a high-impedance state.
sleep mode of the HVD231
The unique difference between the SN65HVD230 and the SN65HVD231 is that both driver and receiver are
switched off in the SN65HVD231 when a logic high is applied to R (pin 8). The device remains in a very low
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power-sleep mode until the circuit is reactivated with a logic low applied to R (pin 8). While in this sleep mode,
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the bus-pins are in a high-impedance state, while the D and R pins default to a logic high.
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 35 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 quality shielded
bus cable.
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