ISL3179EFUZ-T Intersil, ISL3179EFUZ-T Datasheet - Page 10

• Manufacturer Part Number: ISL3179EFUZ-T
• Description: TXRX ESD 3.3V RS-485/422 8-MSOP
• Manufacturer: Intersil
• Type: Transceiverr

Specifications of ISL3179EFUZ-T

• Number Of Drivers/receivers: 1/1
• Protocol: RS422, RS485
• Voltage - Supply: 3 V ~ 3.6 V
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

higher than ±9kV. The RS-485 pins of the ISL3179E survive
±9kV contact discharges, while the ISL3180E’s RS-485 pins
withstand ±5kV.
Hot Plug Function
When a piece of equipment powers up, there is a period of
time where the processor or ASIC driving the RS-485 control
lines (DE, RE) is unable to ensure that the RS-485 Tx and
Rx outputs are kept disabled. If the equipment is connected
to the bus, a driver activating prematurely during power up
may crash the bus. To avoid this scenario, the ISL3179E and
ISL3180E incorporate a “Hot Plug” function. Circuitry
monitoring V
down, the Tx and Rx outputs remain disabled, regardless of the
state of DE and RE, if V
processor/ASIC a chance to stabilize and drive the RS-485
control lines to the proper states.
Data Rate, Cables, and Terminations
RS-485/RS-422 are intended for network lengths up to
4000’, but the maximum system data rate decreases as the
transmission length increases. Devices operating at 40Mbps
are limited to lengths less than 100’.
Twisted pair is the cable of choice for RS-485/RS-422
networks. Twisted pair cables tend to pick up noise and
other electromagnetically induced voltages as common
mode signals, which are effectively rejected by the
differential receiver in this IC.
Proper termination is imperative to minimize reflections. 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
FIGURE 7. HOT PLUG PERFORMANCE (ISL3179E) vs
4
2
0
V
A/Y
RO
CC
CC
ISL83485 WITHOUT HOT PLUG CIRCUITRY
ensures that, during power up and power
2.5V
CC
TIME (40µs/DIV)
ISL3179E
ISL3179E
is less than ~2.4V. This gives the
10
2.3V
DE, DI = V
RE = GND
R
R
L
L
= 1kΩ
= 1kΩ
ISL3179E, ISL3180E
CC
4
2
0
4
2
0
impedance at both ends. Stubs connecting a transceiver to
the main cable should be kept as short as possible.
The ISL3179E, and ISL3180E may also be used at slower
data rates over longer cables, but there are some limitations.
The Rx is optimized for high speed operation, so its output
may glitch if the Rx input differential transition times are too
slow. Keeping the transition times below 500ns, which
equates to the Tx driving a 1000’ (305m) CAT 5 cable, yields
excellent performance over the full operating temperature
range.
Built-In Driver Overload Protection
As stated previously, the RS-485 specification requires that
drivers survive worst case bus contentions undamaged.
These transmitters 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. In the event of a major short circuit
condition, the device also includes 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 reenable
after the die temperature drops about +15°C. If the contention
persists, the thermal shutdown/reenable cycle repeats until
the fault is cleared. Receivers stay operational during thermal
shutdown.
Low Power Shutdown Mode
This BiCMOS transceiver uses a fraction of the power
required by their bipolar counterparts, but it also includes a
shutdown feature that reduces the already low quiescent I
to a 50nA trickle. It enters shutdown whenever the receiver
and driver are simultaneously disabled (RE = V
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 6, 7,
8, 9 and 10, at the end of the “Electrical Specification” table
on page 6, for more information.
CC
April 22, 2008
and
FN6365.2
CC