isl3179e Intersil Corporation, isl3179e Datasheet - Page 8

• Manufacturer Part Number: isl3179e
• Description: ?15kv Esd Protected, +125?c, 40mbps, 3.3v, Full Fail-safe, Rs-485/rs-422 Transceivers
• Manufacturer: Intersil Corporation

Rx outputs deliver large low state currents (typically 28mA at
V
networks.
Receivers easily meet the 40Mbps data rate supported by
the driver, and the receiver output is tri-statable via the active
low RE input.
Driver (Tx) Features
The RS-485/RS-422 driver is a differential output device that
delivers at least 1.5V across a 54Ω load (RS-485), and at
least 2V across a 100Ω load (RS-422). The drivers feature
low propagation delay skew to maximize bit width, and to
minimize EMI.
Outputs of the drivers are not slew rate limited, so faster
output transition times allow data rates of at least 40Mbps.
Driver outputs are tri-statable via the active high DE input.
For parallel applications, bit-to-bit skews between any two
ISL3179E transmitter and receiver pairs are guaranteed to
be no worse than 8ns (4ns max for any two Tx, 4ns max for
any two Rx).
ESD Protection
All pins on the ISL3179E include class 3 (>9kV) Human
Body Model (HBM) ESD protection structures, but the
RS-485 pins (driver outputs and receiver inputs)
incorporate advanced structures allowing them to survive
ESD events in excess of ±16.5kV HBM and ±16.5kV
IEC61000-4-2. The RS-485 pins are particularly vulnerable
to ESD strikes because they typically connect to an
exposed port on the exterior of the finished product. Simply
touching the port pins, or connecting a cable, can cause an
ESD event that might destroy unprotected ICs. These new
ESD structures protect the device whether or not it is
powered up, and without degrading the RS-485 common
mode range of -7V to +12V. This built-in ESD protection
eliminates the need for board level protection structures
(e.g., transient suppression diodes), and the associated,
undesirable capacitive load they present.
IEC61000-4-2 Testing
The IEC61000 test method applies to finished equipment,
rather than to an individual IC. Therefore, the pins most likely
to suffer an ESD event are those that are exposed to the
outside world (the RS-485 pins in this case), and the IC is
tested in its typical application configuration (power applied)
rather than testing each pin-to-pin combination. The
IEC61000 standard’s lower current limiting resistor coupled
with the larger charge storage capacitor yields a test that is
much more severe than the HBM test. The extra ESD
protection built into this device’s RS-485 pins allows the
design of equipment meeting level 4 criteria without the need
for additional board level protection on the RS-485 port.
OL
= 1V) to ease the design of optically coupled isolated
8
ISL3179E
AIR-GAP DISCHARGE TEST METHOD
For this test method, a charged probe tip moves toward the
IC pin until the voltage arcs to it. The current waveform
delivered to the IC pin depends on approach speed,
humidity, temperature, etc., so it is more difficult to obtain
repeatable results. The ISL3179E RS-485 pins withstand
±16.5kV air-gap discharges.
CONTACT DISCHARGE TEST METHOD
During the contact discharge test, the probe contacts the
tested pin before the probe tip is energized, thereby
eliminating the variables associated with the air-gap
discharge. The result is a more repeatable and predictable
test, but equipment limits prevent testing devices at voltages
higher than ±9kV. The RS-485 pins of the ISL3179E survive
±9kV contact discharges.
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
incorporates a “Hot Plug” function. Circuitry monitoring V
ensures that, during power up and power down, the Tx and Rx
outputs remain disabled, regardless of the state of DE and RE,
if V
chance to stabilize and drive the RS-485 control lines to the
proper states.
FIGURE 7. HOT PLUG PERFORMANCE (ISL3179E) vs
CC
4
2
0
V
is less than ~2.4V. This gives the processor/ASIC a
A/Y
RO
CC
ISL83485 WITHOUT HOT PLUG CIRCUITRY
2.5V
TIME (40μs/DIV)
ISL3179E
ISL3179E
2.3V
DE, DI = V
RE = GND
R
R
L
L
= 1kΩ
= 1kΩ
August 16, 2007
CC
FN6365.1
CC
4
2
0
4
2
0