FN6085 Datasheet, PDF (12/19 Pages) Intersil Corporation – ±15kV ESD, 5V, Full Fail-Safe, 1/8 Unit Load, RS-485/RS-422 Transceivers

ISL83080E, ISL83082E, ISL83083E, ISL83084E, ISL83085E, ISL83086E, ISL83088E
115kbps versions need not be terminated, but, terminations
are recommended unless power dissipation is an overriding
concern.
In point-to-point, or point-to-multipoint (single driver on bus)
networks, the main cable should be terminated in its
characteristic impedance (typically 120Ω) at the end farthest
from the driver. In multi-receiver applications, stubs
connecting receivers to the main cable should be kept as
short as possible. Multipoint (multi-driver) systems require
that the main cable be terminated in its characteristic
impedance at both ends. Stubs connecting a transceiver to
the main cable should be kept as short as possible.
Built-In Driver Overload Protection
As stated previously, the RS-485 specification requires that
drivers survive worst case bus contentions undamaged.
These devices meet this requirement via driver output short
circuit current limits, and on-chip thermal shutdown circuitry.
The driver output stages incorporate short circuit current
limiting circuitry which ensures that the output current never
exceeds the RS-485 specification, even at the common
mode voltage range extremes. Additionally, these devices
utilize a foldback circuit which reduces the short circuit
current, and thus the power dissipation, whenever the
contending voltage exceeds either supply.
In the event of a major short circuit condition, devices also
include a thermal shutdown feature that disables the drivers
whenever the die temperature becomes excessive. This
eliminates the power dissipation, allowing the die to cool. The
drivers automatically re-enable after the die temperature
drops about +15°C. If the contention persists, the thermal
shutdown/re-enable cycle repeats until the fault is cleared.
Receivers stay operational during thermal shutdown.
Low Power Shutdown Mode
These CMOS transceivers all use a fraction of the power
required by their bipolar counterparts, but they also include a
shutdown feature (except for the ISL83084E) that reduces
the already low quiescent I_CC to a 70nA trickle. These
devices enter shutdown whenever the receiver and driver
are simultaneously disabled (RE = V_CC and DE = GND) for
a period of at least 600ns. Disabling both the driver and the
receiver for less than 60ns guarantees that the transceiver
will not enter shutdown.
Note that receiver and driver enable times increase when
the transceiver enables from shutdown. Refer to Notes 8
thru 12, at the end of the “Electrical Specification Table” on
page 8, for more information.
Typical Performance Curves V_CC = 5V, T_A = +25°C; Unless Otherwise Specified
90
3.4
80
3.2
70
R_DIFF = 100Ω
3.0
60
50
2.8
40
2.6
30
2.4
R_DIFF = 54Ω
20
2.2
10
0
0
1
2
3
4
5
DIFFERENTIAL OUTPUT VOLTAGE (V)
FIGURE 8. DRIVER OUTPUT CURRENT vs DIFFERENTIAL
OUTPUT VOLTAGE
2.0
-40 -25
0
25
50
75 85
TEMPERATURE (°C)
FIGURE 9. DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs
TEMPERATURE
12
FN6085.9
April 22, 2008