ADM3055EBRIZ datasheet(21/24 Pages) AD

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Data Sheet

ADM3055E/ADM3057E

Rev. B | Page 21 of 24

RS PIN

The RS pin sets the transceiver in one of three different modes

of operation: high speed, slope control, or standby. This pin

cannot be left floating.

For high speed mode, connect the RS pin directly to GND2.

Ensure that the transition time of the CAN bus signals are as

short as possible to allow higher speed signaling. A shielded

cable is recommended to avoid electromagnetic interference

(EMI) problems in high speed mode.

Slope control mode allows the use of unshielded twisted pair

wires or parallel pair wires as bus lines. Slow the signal rise and

fall transition times to reduce EMI and ringing in slope control

mode. Adjust the rise and fall slopes by adding a resistor (RSLOPE)

connected from RS to GND2. The slope is proportional to the

current output at the RS pin.

The RS pin can also set the CAN transceiver to standby mode,

which occurs when the pin is driven to a voltage above VSTB. In

standby mode, high speed data is filtered, and the CANH and

CANL lines are biased to GND2.

The RS pin can only set the CAN transceiver to standby mode.

The state of the RS pin does not modify the operation of digital

isolation channels or the auxiliary channel.

AUXILIARY CHANNEL

The auxiliary channel is available for low speed data transmission

at up to 20 kHz (or 40 kbps nonreturn-to-zero format) when

STBY is not asserted. The data rate limit of the channel allows the

data channel to be shared by the STBY signal.

In standby mode, or when STBY is driven high, the operation of

the channel is modified to share the multiplexed signal path

with the STBY signal (see Figure 1). The AUXOUT pin remains

latched in the state when STBY is asserted. Periodic pulses

(<25 µs wide) are sent to indicate that the logic side is powered

and remains in standby mode.

In applications where AUXOUT may be shorted to GND2 or VDD2,

add a series resistance to the output channel.

An example of using this auxiliary channel to control a switchable

termination from the logic side is demonstrated on the EVAL-

ADM3055EEBZ evaluation board.

INTEGRATED AND CERTIFIED IEC EMC SOLUTION

Typically, designers must add protections against harsh operating

environments while also making the product as small as possible.

To reduce board space and the design effort needed to meet system

level ESD standards, the ADM3055E and the ADM3057E include

robust protection circuitry on chip for the CANH and CANL lines.

FAULT PROTECTION

Miswire events commonly occur when the system power supply

is connected directly to the CANH and CANL bus lines during

assembly. The ADM3055E and the ADM3057E CAN bus pins

are protected against such high voltage miswire events. The

ADM3055E and the ADM3057E CANH and CANL signal lines

can withstand continuous ±40 V with respect to GND2 or +40 V

between the CAN bus lines without damage. This level of

protection applies when the device is either powered or

unpowered.

The ADM3055E provides IEC 61000-4-2 Level 4 ESD protection,

but some applications may require further system level protection.

The symmetrical nature of the ADM3055E ±40 V bus fault

protection and the ±25 V CMR makes the selection of

bidirectional transient voltage suppressor (TVS) diodes easier.

FAIL-SAFE FEATURES

In cases where the TXD input pin is allowed to float, to prevent

bus traffic interruption, the TXD input channel has an internal

pull-up to the VIO pin. The pull-up holds the transceiver in the

recessive state.

The ADM3055E and the ADM3057E feature a dominant timeout

(tDT in Table 2). A TXD line shorted to ground or malfunctioning

CAN controller are examples of how a single node can indefinitely

prevent further bus traffic. The dominant timeout limits how

long the dominant state can transmit to the CAN bus by the

transceiver. When the TXD pin is presented with a logic high,

normal TXD functionality is restored.

The tDT minimum also inherently creates a minimum data rate.

Under normal operation, the CAN protocol allows five consecutive

bits of the same polarity before stuffing a bit of the opposite

polarity into the transmitting bit sequence. When an error is

detected, the CAN controller purposely violates the bit stuffing

rules by producing six consecutive dominant bits. At any given

data rate, the CAN controller must transmit as many as 11

consecutive dominant bits to effectively limit the ADM3055E

and the ADM3057E minimum data rate to 9600 bps.

THERMAL SHUTDOWN

The ADM3055E and the ADM3057E contain thermal

shutdown circuitry that protects the devices from excessive

power dissipation during fault conditions. Shorting the driver

outputs to a low impedance source can result in high driver

currents. The thermal sensing circuitry detects the increase in

die temperature under this condition and disables the driver

outputs. The circuitry disables the driver outputs when the die

temperature reaches 175°C. When the die has cooled, the

drivers are enabled again.

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