ISL3283EFHZ-T Datasheet, PDF (10/15 Pages) Integrated Device Technology – ±16.5kV ESD Protected, +125°C, 3.0V to 5.5V, SOT-23/TDFN Packaged, 20Mbps, Full Fail-safe, Low Power, RS-485/RS-422 Receivers

ISL3280E, ISL3281E, ISL3282E, ISL3283E, ISL3284E, ISL3285E
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 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.
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 difficult to obtain
repeatable results. The A and B 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 ISL3280E, ISL3281E, ISL3282E,
ISL3283E, ISL3284E, ISL3285E survive ±9kV contact
discharges on the RS-485 pins.
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. Networks operating at
20Mbps are limited to lengths less than 100’, while a
250kbps network that uses slew rate limited transmitters can
operate at that data rate over lengths of several thousand
feet.
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 these ICs.
To minimize reflections, proper termination is imperative for
high data rate networks. Short networks using slew rate
limited transmitters 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 transmitter or
receiver to the main cable should be kept as short as
possible.
Low Power Shutdown Mode
These BiCMOS receivers all use a fraction of the power
required by their bipolar counterparts, and the versions with
output enable functions include a shutdown feature that
reduces the already low quiescent I_CC to a 20µA trickle.
These versions enter shutdown whenever the receiver
disables (RE = V_CC or RE = GND).
Typical Performance Curves C_L = 15pF, T_A = +25°C; Unless Otherwise Specified.
0.50
250
0.45
V_CC = V_L = 5V
V_CC = 5V OR 3.3V
0.40
V_CC = V_L = 3.3V
200
0.35
0.30
150
0.25
V_L = 5V, V_CC = 5V ONLY
0.20
100
0.15
0.10
0.05
RE = V_CC, RE = 0V
0
-40
-15
10
35
60
85 110 125
TEMPERATURE (°C)
V_L ≤ 1.8V
50
V_L = 3.3V
V_L = 2.5V
0
0
1
2
3
4
5
6
7 7.5
RE VOLTAGE (V)
FIGURE 4. SUPPLY CURRENT vs TEMPERATURE
FIGURE 5. V_L SUPPLY CURRENT vs ENABLE PIN VOLTAGE
10
FN6543.2
October 18, 2007