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IL41050TE

Isolated High-Speed CAN Transceiver

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IL41050

Application Information

VDD2 Power Supply Pins

Both VDD2 power supply inputs (pins 11 and 16) must be connected to the bus-side power supply. Pin 11 powers the bus side of the CAN I/O

circuitry, while pin 16 powers the bus-side isolation circuitry. For testing purposes, they are not internally connected, but the part will not operate

without both pins powered, and operation without both pins powered can cause damage.

Power Supply Decoupling

Both VDD1 and VDD2 must be bypassed with 100 nF ceramic capacitors. These supply the dynamic current required for the isolator switching and

should be placed as close as possible to VDD and their respective ground return pins.

Input Configurations

The TxD input should not be left open as the state will be indeterminate. If connected to an open-drain or open collector output, a pull-up resistor

(typically 16 kΩ) should be connected from the input to VDD1.

The Mode Select (“S”) input has a nominal 150 kΩ internal pull-down resistor. It can be left open or set low for normal operation.

Dominant Mode Time-out and Failsafe Receiver Functions

CAN bus latch up is prevented by an integrated Dominant mode timeout function. If the TxD pin is forced permanently low by hardware or

software application failure, the time-out returns the RxD output to the high state no more than 765 μs after TxD is asserted dominant. The timer

is triggered by a negative edge on TxD. If the duration of the low is longer than the internal timer value, the transmitter is disabled, driving the

bus to the recessive state. The timer is reset by a positive edge on pin TxD.

If power is lost on Vdd2, the IL41050 asserts the RxD output high when the supply voltage falls below 3.8 V. RxD will return to normal

operation as soon as Vdd2 rises above approximately 4.2 V.

Programmable Power-Up

A unique non-volatile programmable power-up feature prevents unstable nodes. A state that needs to be present at node power up can be

programmed at the last power down. For example if a CAN node is required to “pulse” dominant at power up, TxD can be sent low by the

controller immediately prior to power down. When power is resumed, the node will immediately go dominant allowing self-check code in the

microcontroller to verify node operation. If desired, the node can also power up silently by presetting the TxD line high at power down. At the

next power on, the IL41050 will remain silent, awaiting a dominant state from the bus.

The microcontroller can check that the CAN node powered down correctly before applying power at the next “power on” request. If the node

powered down as intended, RxD will be set high and stored in IL41050’s non-volatile memory. The level stored in the RxD bit can be read

before isolated node power is enabled, avoiding possible CAN bus disruption due to an unstable node.

Replacing Non-Isolated Transceivers

The IL41050 is designed to replace common non-isolated CAN transceivers such as the Philips/NXP TJA1050 with minimal circuit changes.

Some notable differences:

• Some non-isolated CAN transceivers have internal TxD pull-up resistors, but the IL41050 TxD input should not be left open. If

connected to an open-drain or open collector output, a pull-up resistor (typically 16 kΩ) should be connected from the input to VDD1.

• Initialization behavior varies between CAN transceivers. To ensure the desired power-up state, the IL41050 should be initialized with a

TxD pulse (low-to-high for recessive initialization), or shut down the transceiver in the desired power-up state (the “programmable

power-up feature”).

• Many non-isolated CAN transceivers have a VREF output. Such a reference is available on the IL41050 wide-body version.

The VREF Output

VREF is a reference voltage output used to drive bus threshold comparators in some legacy systems and is provided on the IL41050 wide-body

version. The output is half of the bus supply ±10% (i.e., 0.45 VDD2 < VREF < 0.55 VDD2), and can drive up to 50 µA.

IsoRxD / IsoTxD Outputs

The IsoRxD and IsoTxD outputs are isolated versions of the RxD and TxD signals. These outputs are provided on the narrow-body version for

troubleshooting, but normally no connections should be made to the pins.

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NVE Corporation 11409 Valley View Road Eden Prairie, MN 55344-3617 USA Telephone: (952) 829-9217 Fax (952) 829-9189 Internet: www.isoloop.com

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