Isolated RS485 µModule Transceiver Integrates Isolated Power

24th May 2010

ES Admin

0 0

Datasheet

Linear Technology has introduced the LTM2881, an isolated RS485 µModule transceiver that guards against large ground-to-ground differentials and common mode transients. In practical RS485 systems, ground potentials vary widely from node to node, often exceeding the tolerable range, which can result in an interruption of communications or destruction of a transceiver. The LTM2881 breaks ground loops by isolating the logic level interface and line transceiver using internal inductive signal isolation that allows for a much larger common mode voltage range plus superior common mode rejection of >30kV/µS.

A low EMI DC-DC converter powers the transceiver and provides an isolated 5V supply output for powering any supporting external components. With 2,500VRMS of galvanic isolation, onboard secondary power and a fully compliant RS485 transmitter and receiver, the LTM2881 requires no external components, ensuring a complete, small µModule solution for isolated serial data communications.

The features of the LTM2881 make it suitable for a wide range of applications, including breaking ground loops, working with large common mode voltages and when using multiple unterminated line taps. The ±15kV ESD-protected transceiver operates at 20Mbps or low EMI 250kbps, in half-duplex or full-duplex configurations. The driver maintains high impedance over the entire common mode range and has a short circuit current limit, as well as slew rate control for minimizing EMI. Its counterpart, the failsafe receiver, allows up to 256 devices to be connected on the same lines and defaults to a logic '1' if the receiver inputs are open, shorted or terminated but not driven, all without the need to pre-bias the network. Integrated selectable termination allows cables to be properly terminated to avoid signal reflections and distorted waveforms, with the flexibility to add or remove termination anywhere onto the bus via a software switch. The device also features thermal shutdown protection, disabling the transceiver outputs in case of excessive power dissipation. Users will appreciate how the self-powered LTM2881 takes many precautions to guarantee safe and reliable communications in RS485 or RS422 systems.

Two versions of the LTM2881 are available to support 3.3V and 5V input supply voltages. The LTM2881 is available in low profile 11.25 x 15mm x 2.8mm surface mount LGA and BGA packages. All integrated circuits and passive components are housed in this Linear Technology, RoHS-compliant µModule package.