LTC491IN#PBF

Drivers, Receivers, Transceivers Overview

The LTC491IN#PBF is a low-power, full-duplex differential bus transceiver designed for RS-485 and RS-422 applications. It operates from a single 5V supply with a typical supply current of 300mA. The device supports data rates up to 2.5Mbps with typical driver propagation delays of 28ns and skew of 5ns. It features an extended common-mode range of –7V to 12V and includes thermal shutdown protection. The receiver incorporates a fail-safe feature that guarantees a high output state when inputs are open. The component is available in 14-lead PDIP and SO packages.

Drivers, Receivers, Transceivers Feature Summary

• Thermal shutdown circuit prevents excessive power dissipation by forcing driver outputs into a high impedance state during overheating.
• Fail-safe receiver design ensures a known high logic state when differential inputs are left floating or disconnected.
• Glitch-free driver outputs permit live insertion or removal of the package without generating signal spikes.
• CMOS construction provides significant power savings compared to bipolar counterparts while maintaining ESD ruggedness.

Drivers, Receivers, Transceivers Applications

• Multipoint data transmission systems adhering to RS-485 standards
• Full-duplex communication links compliant with RS-422 protocols
• Line repeater configurations for extending cable lengths beyond standard limits

Drivers, Receivers, Transceivers Procurement Notes

Verify the specific suffix matches the required operating temperature range and package type. The 'I' designation indicates an industrial temperature range of –40°C to 85°C, whereas 'C' denotes commercial range. Confirm pin compatibility with existing designs, as the device is pin-compatible with the SN75180. Ensure supply voltage constraints between 4.75V and 5.25V are met for proper operation.

Drivers, Receivers, Transceivers Selection Notes

Select this component for applications requiring low power consumption on a 5V supply with extended common-mode voltage tolerance. It is suitable for environments where thermal protection and glitch-free operation during hot-swapping are critical. Consider the 2.5Mbps speed limit and 32-node bus capacity when designing network topology. Verify that the 70mV input hysteresis meets noise immunity requirements for the specific cabling environment.

Drivers, Receivers, Transceivers Part Context

The LTC491 is part of Linear Technology's (now Analog Devices) RS-485/RS-422 transceiver family. It serves as a low-power alternative to older bipolar devices like the SN75180. The device is pin-compatible with industry-standard parts, facilitating direct upgrades in existing designs. Related components include the LTC490 for half-duplex applications and higher-speed variants like the LTC1686.

Drivers, Receivers, Transceivers Replacement Considerations

The SN75180 is a confirmed pin-compatible substitute. The LTC1686/LTC1687 series offers pin compatibility with higher speed capabilities. Verify that replacement parts maintain the same 5V supply requirement and thermal shutdown characteristics if those features are essential to the design.

Drivers, Receivers, Transceivers FAQ

How does the LTC491 handle bus contention faults?

The device includes a thermal shutdown circuit that disables driver outputs when internal temperature reaches 150°C. However, this protection may not activate if multiple drivers are shorted directly together, as the current may be insufficient to trigger the thermal sensor.

What is the behavior of the receiver when inputs are open?

The LTC491 features a fail-safe mechanism that guarantees the receiver output remains in a high logic state when the differential inputs A and B are left floating or disconnected.

Can the LTC491 be used for AC coupled termination schemes?

Yes, the datasheet describes using AC coupling capacitors at the termination resistors to eliminate DC current flow. The capacitor value should be calculated based on line length, typically 16.3pF per foot for 120Ω cables.