1. Overview & Purpose

️· Device: LTC490 is a line driver/receiver for RS-485 communication. It facilitates full-duplex data transmission over twisted-pair cables.
️· Function: Drives and receives data signals for RS-485 networks.
️· Complementary Part: LTC491 offers the same functionality but with disableable outputs.

2. Key Features

️· RS-485 Compliance: Designed for RS-485 communication standards.
️· Full-Duplex Operation: Supports simultaneous transmitting and receiving.
️· Thermal Shutdown: Built-in protection circuit to prevent damage from excessive power dissipation (disables driver outputs when internal temperature reaches 150°C).
️· ESD Protection: Protected against electrostatic discharge (ESD) transients up to 2kV.
️· Data Rate: Suitable for data rates appropriate for RS485 applications.
️· Line Repeater Capability: Can be used to extend cable length beyond standard limits (up to 4000 feet).

3. Application Circuits & Recommendations

️· Typical Connection (Figure 5): Two twisted-pair wires connect driver/receiver pairs. Driver and receiver outputs are always enabled.
️· Line Repeater (Figure 6): Inserts the LTC490 midway along a cable longer than 4000 feet, connecting the receiver output back to the driver input.
️· Cable Termination:
- Typically requires 120Ω termination resistors at the cable ends.
- AC Coupling (Figure 10): Recommended to reduce power consumption by using capacitors to block DC current through termination resistors. (C = line length (ft) × 16.3pF)
️· ESD Protection (Figure 11): Implement protection by connecting bidirectional TransZorbs from line side pins to ground.

4. Electrical Characteristics and Considerations

️· Thermal Shutdown: Disables driver outputs at 150°C, re-enables at 130°C. *Crucially, multiple drivers shorted together may not trigger this protection, leading to contention faults.*
️· Cable Choice: Twisted-pair cables are preferred.
️· DC Power Consumption: DC current flows in the cable when termination resistors are used, leading to power consumption. AC coupling mitigates this.

5. Important Notes & Warnings

️· Output Enable: Driver and receiver outputs are *always* enabled.
️· Contention: Thermal shutdown may not prevent contention faults when multiple drivers are active.
️· Power Savings with AC Coupling: Power consumption is minimized when data rates are lower than 1/(120Ω * C), where C is the coupling capacitor value.
️· TransZorb Selection: When implementing ESD protection with TransZorbs, choose a breakdown voltage higher than the common-mode voltage and be mindful of added parasitic capacitance.

Summary Table

Feature	Description
Device Type	RS-485 Driver/Receiver
Data Rate	Suitable for RS485 data rates
Termination	Requires 120Ω termination resistors; AC coupling recommended
Thermal Shutdown Temp	150°C
ESD Protection	Up to 2kV
Cable Type	Twisted pair

Disclaimer: This summary is based solely on the provided text and may not capture all nuances of the full LTC490 datasheet. Refer to the complete datasheet for comprehensive details and specifications.