Electronic Design

Dual RS232/RS485 IC Integrates Switchable Termination

LinearTech-AThe LTC2872 is a multiprotocol 20-Mbit/s RS232 and 500-Kbit/s RS485 transceiver with switchable integrated termination for 3.3-V and 5-V systems. RS485 systems require a termination resistor on the ends of the communication bus to minimize signal reflections. The LTC2872 integrates pin-controlled termination resistors for easy interface reconfiguration, eliminating external resistors and control relays. The termination resistors, when enabled, are automatically switched in or out to match the transceiver’s protocol selection of RS232 (120-Ω termination) or RS485 (5-KΩ termination). The device also features high ESD protection of ±16 kV HBM on the transceiver bus pins, when powered off or operating. The device can be configured as four RS232 single-ended transceivers or two RS485 differential transceivers, or combinations of both, on shared I/O lines, reducing component count for multiprotocol networks, offering on-the-fly configurability. It features half-/full-duplex RS485 switching, a logic loopback mode, and a 1.7-V to 5.5-V logic interface. The LTC2872 is suitable for a wide range of applications, including software-selectable multiprotocol interface ports, point-of-sale terminals, security cameras, cable repeaters and protocol translators. Drivers and receivers are independently disabled, leaving them in a high impedance state, consuming only 9 µA in a low-power shut-down mode. Other protective measures include high ESD of ±4 kV or better on all pins, thermal shutdown protection and a full failsafe RS485 receiver for floating, shorted or terminated inputs that eliminates UART lockup and the need for external network biasing resistors. The LTC2872 is available in a 38-pin 5-by-7-mm QFN package and is available today in production quantities. Pricing starts at $6.45 each in 1,000 piece quantities.


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