LTC1535CSW#PBF Linear Technology, LTC1535CSW#PBF Datasheet - Page 11

• Manufacturer Part Number: LTC1535CSW#PBF
• Description: IC TRANSCEIVER RS485 ISO 28SOIC
• Manufacturer: Linear Technology
• Type: Transceiverr

Specifications of LTC1535CSW#PBF

• Number Of Drivers/receivers: 1/1
• Protocol: RS485
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (7.5mm Width)
• Device Type: Differential
• Interface Type: RS422, RS485
• No. Of Drivers: 1
• Supply Voltage Range: 4.5V To 7.5V
• Driver Case Style: SOIC
• No. Of Pins: 28
• Operating Temperature Range: 0°C To +70°C
• Svhc: No
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
Driver Output and Slow Slew Rate Control
The LTC1535 uses a proprietary driver output stage that
allows a common mode voltage range that extends beyond
the power supplies. Thus, the high impedance state is
maintained over the full RS485 common mode range.
The output stage provides 100mA of short-circuit current
limiting in both the positive and negative directions. Thus,
even under short-circuit conditions, the supply voltage
from the open-loop DC converter will remain high enough
for proper communication across the isolation barrier. The
driver output will be disabled in the event of a thermal
shutdown and a fault condition will be indicated through
the RE weak output.
The CMOS level SLO pin selects slow or fast slew rates
on the RS485 driver output (see Figures 15, 16, 17, 18 for
typical waveforms). The SLO input has an internal 100k
pull-up resistor. When SLO is low, the driver outputs are
slew rate limited to reduce high frequency edges. Left open
or tied high, SLO defaults to fast edges. The part draws
more current during slow slew rate edges.
FAULT
FAULT
FAULT INDICATED WHEN RE IS THREE-STATED
POLL
POLL
RE
Figure 11. Detecting Fault Conditions
BUFFER
Monitoring Faults on RE
The RE pin can be used to monitor the following fault
conditions: low supply voltages, thermal shutdown or
a time-out fault when there is no data communication
across the barrier. During a fault, the receiver output,
RO, defaults to a high state (see Table 2). Open circuit or
short-circuit conditions on the twisted pair do not cause
a fault indication. However, the RS485 receiver defaults
to a high output state when the receiver input is open or
short-circuited.
The RE pin has a weak current drive output mode for
indicating fault conditions. This fault state can be polled
using a bidirectional microcontroller I/O line or by using
the circuit in Figure 11, where the control to RE is three-
stated and the fault condition read back from the RE pin.
The weak drive has 100μA pull-up current to indicate a
fault and 50μA pull-down current for no fault. This allows
the RE pin to be polled without disabling RE on nonfault
conditions.
Both sides contain a low voltage detect circuit. A
voltage less than 4.2V on the isolated side disables
communication.
RO
RE
DI
DE
FAULT
GND
V
V
CC
CC
LTC1535
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LTC1535
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