3.3-V/5-V multiprotocol transceivers provide integrated switchable termination
December 09, 2010 // Paul Buckley
Linear Technology Corporation has introduced the LTC2870 and LTC2871 multiprotocol transceivers 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.
Both the LTC2870 and LTC2871 integrate pin-controlled termination resistors that allow for easy interface reconfiguration, eliminating external resistors and control relays. The termination resistors, when enabled, are automatically switched on or out to match the transceiver's protocol selection of RS232 or RS485. Both devices also feature high ESD protection: ±26 kV HBM (LTC2870) or ±16 kV HBM (LTC2871) on the transceiver bus pins, when powered off or operating.
The LTC2870 can be configured as two RS232 single-ended transceivers or one RS485 differential transceiver on shared I/O lines, whereas the LTC2871 offers independent control of two RS232 transceivers and one RS485 transceiver, each on dedicated I/O lines. Both devices reduce component count for multiprotocol networks and offer on-the-fly configurability.
The LTC2870 and LTC2871 are suitable for a wide variety of applications, including software-selectable multiprotocol interface ports, point-of-sale terminals, security cameras, cable repeaters and protocol translators.
An optional 1.7 V to 5.5 V logic supply enables convenient digital interfacing, and an integrated DC/DC boost converter eliminates the need for multiple supplies to drive RS232 levels. Drivers and receivers can be independently disabled, leaving them in a high impedance state, consuming only 9 µA in a low power shutdown mode. Aside from automatic termination selection, both devices provide half- and full-duplex RS485 switching and a logic loopback mode that steers the driver inputs to the receiver outputs for diagnostic self-test and debug.
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 the need for external network biasing resistors and UART lockup.
The LTC2870 is available in 28-pin 4 mm x 5 mm QFN and TSSOP packages, and the LTC2871 is available in 38-pin 5 mm x 7 mm QFN and TSSOP packages. Both devices are available today in production quantities, priced starting at $5.00 each in 1,000 piece quantities.
More information about the LTC2870 and LTC2871 multiprotocol transceivers at www.linear.com/2870
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