RS485 Transceivers Reduce Power and EMI – Design Note 102
Dave Dwelley, Teo Yang Long, Yau Khai Cheong and Bob Reay
Recent innovations in process and circuit design have
enabled the release of three new RS485 transceivers:
the LTC В®1481, LTC1483 and LTC1487. These devices
share an improved receiver circuit which features 80ОјA
quiescent current operation (driver disabled) with no
loss in AC performance relative to standard RS485
devices, and a new 1ОјA shutdown mode (Figure 1). All
three new devices are pin compatible with the industry
standard LTC485 pinout, and feature Linear Technology’s exclusive ±10kV ESD protection (Human Body
Model) at the line I/O pins, eliminating the need for
external ESD protection in most cases. LTC1483
The LTC1483 is a reduced EMI version of the LTC1481
intended for use in systems where electromagnetic
interference concerns take precedence over high data
rates. The LTC1483 driver slew rate is deliberately limited
to reduce the high frequency electromagnetic emissions
(Figures 2a and 2b) while improving signal п¬Ѓdelity by
reducing reflections due to misterminated cables. The
maximum operating frequency of the LTC1483 driver is
limited to 250kbaud. All other performance parameters
are unchanged from the LTC1481, including the low …