Recessive

Dominant

Recessive

Time, t

Low Power

Standby Mode

CANL

CANH

V

diff

V

diff

Normal & Silent Mode

RXD

V /2

CC

A

B

A: Normal Mode

B: Low Power Standby Mode

CANH

CANL

HVDA551-Q1

HVDA553-Q1

SLLSEC4 – JUNE 2013

www.ti.com

Table 3. Operating Modes

DEVICE

STB

MODE

DRIVER

RECEIVER

RXD Pin

LOW

Normal Mode

Enabled (On)

Enabled (On)

Standby mode

Low-power wake-up

All Devices

HIGH

(RXD wake-up

Disabled (Off)

receiver and bus

request)

monitor enabled

(1)

Mirrors bus state: LOW if CAN bus is dominant, HIGH if CAN bus is recessive.

(2)

See Figure 5 and Figure 6 for operation of the low-power wake-up receiver and bus monitor for RXD wake-up request behavior and

Table 5 for the wake -up receiver threshold levels.

Bus States by Mode

The CAN bus has three valid states during powered operation, depending on the mode of the device. In normal

mode the bus may be dominant (logic LOW), where the bus lines are driven differentially apart, or recessive

receiver. The third state is low-power standby mode where the bus lines are biased to GND via the high-ohmic

Figure 3. Bus States (Physical Bit Representation)

Figure 4. Simplified Common-Mode Bias and

Receiver Implementation

Normal Mode

This is the normal operating mode of the device. Normal mode is selected by setting STB low. The CAN driver

and receiver are fully operational and CAN communication is bidirectional. The driver is translating a digital input

on TXD to a differential output on CANH and CANL. The receiver is translating the differential signal from CANH

and CANL to a digital output on RXD. In recessive state, the CAN bus pins (CANH and CANL) are biased to 0.5

bus, and logic low is equivalent to a dominant (differential) signal on the bus.

Standby Mode With RXD Wake-Up Request

This is the low-power mode of the device. Standby mode is selected by setting STB high. The CAN driver and

main receiver are turned off and bidirectional CAN communication is not possible. The low-power receiver and

controller (MCU) should monitor RXD for transitions and then reactivate the device to normal mode based on the

mode if it has been turned off for low-power standby operation. The CAN bus pins are weakly pulled to GND, see

Figure 3 and Figure 4.

4

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