LTC2875
12
2875f
For more information www.linear.com/LTC2875
Supply Voltage Ranges
The LTC2875 can operate from 3.3V or 5V supplies. An in-
ternal compa
rator moni
tors the supply voltage and switches
internal reference voltages and output drive strengths at
approximately 4.1V. Because of the discontinuity in the
internal voltages at this switch point, operation with a sup
-
ply voltage between 3.6V and 4.5V is not recommended.
±60V Fault Protection
The
LTC2875 addresses application needs for an overvolt
-
age tolerant CAN transceiver that can operate from both
3.3V and 5V supplies and provide extended common mode
operation, high noise immunity and low electromagnetic
emission. Industrial installations may encounter common
mode voltages between nodes far greater than the –2V to
7V range specified by the ISO 11898-2 standard. Compet
-
ing CAN transceivers can be damaged by voltages beyond
their typical absolute maximum ratings of –3V to 16V.
The limited overvoltage tolerance makes implementation
of effective external protection networks difficult without
interfering with proper data network performance. Replac
-
ing standard
CAN transceivers with LTC2875 devices can
eliminate
field failures due to overvoltage faults without
using costly external protection devices.
The ±60V fault protection of the LTC2875 is achieved by
using a high voltage BiCMOS integrated circuit technology.
The naturally high
breakdown voltage of this technology
provides
protection in powered off and high impedance
conditions. The driver outputs use a progressive foldback
current limit to protect against overvoltage faults while
still allowing high current output drive.
The LTC2875 is protected from ±60V bus faults even
with the loss of GND or V
CC
(GND open faults are not
tested in production). In the case of V
CC
open, or shorted
to GND, the LTC2875 is off and the bus pins remain in
the high impedance state. Additional precautions must
be taken in the case of V
CC
present and GND open. The
LTC2875 chip protects itself from damage but may turn
on despite the open GND pin. When the RS or TXD input
is pulled low with the GND pin floating, a sneak path to
GND is established: through the ESD diode on the RS
or TXD pin; out through the RS or TXD pin; and into
the external driver that is pulling the pin low (Figure 8).
applicaTions inForMaTion
The current in this path can have a maximum current of
–100mA with a maximum voltage of approximately V
CC
– 2.5V during an overvoltage fault condition on the CANL
pin because
the entire current that should flow out the
GND
pin may flow out the input pin instead. If a GND open
fault with V
CC
present is anticipated, the system designer
should choose drivers for the RS and TXD inputs that are
protected against shorts to V
CC
– 2.5V.
The high voltage rating of the LTC2875 makes it simple
to extend the overvoltage protection to higher levels us
-
ing external protection components. Compared to lower
voltage CAN transceivers, external protection devices with
higher breakdown voltages can be used so as not to interfere
with data transmission in the presence of large common
mode voltages. Figure 13 in the Typical Applications sec
-
tion shows
a network capable of protecting against IEC
Level
4 surge, while still providing up to ±35V common
mode range on the signal lines.
Figure 8. Sneak Path to GND with GND Pin Floating
±36V Extended Common Mode Range
The LTC2875 receiver features an extended common mode
range of –36V to 36V when operating from a 5V supply,
and –25V to 25V when operating from a 3.3V supply. The
wide common mode increases the reliability of operation in
environments with high common mode voltages created by
electrical noise or local ground potential
differences due to
ground loops. This extended common mode range allows
the LTC2875 to transmit and receive under conditions that
would cause data errors and possible device damage in
competing products.
RXD
TXD
TXD
GND
V
CC
RXD
V
CC
V
CC
LTC2875
RS
CANH
RSB
CANH
CANL
SPLIT
CANL
SPLIT
