ISL32610E Datasheet, PDF (7/12 Pages) Intersil Corporation – 16.5kV ESD Protected, 1.8V, Micro Power, 125°C, 1/8 Unit Load, RS-485/RS-422 Differential Receivers

ISL32610E, ISL32611E, ISL32612E
Application Information
Features
These devices utilize a differential input receiver for maximum
noise immunity and common mode rejection. Input sensitivity is
±200mV, as required by the RS-422 and RS-485 standards.
These receivers’ symmetrical ±200mV switching thresholds
deliver less duty cycle distortion than similar receivers with a
full-failsafe design (i.e., skewed low/high input thresholds, (such
as -200mV/-20mV) which increase the high bit width). This
distortion is especially noticeable when the Rx is driven by slow
input transitions (see Figure 2).
The symmetrical input thresholds also allow more room for
increased input hysteresis, thereby increasing the Rx noise
immunity. The 70mV hysteresis of this Rx is twice the amount
specified for most full-failsafe devices.
Receiver input resistance of 96kΩ surpasses the RS-422
specification of 4kΩ, and is eight times the RS-485 “Unit Load
(UL)” requirement of 12kΩ minimum. Thus, these products are
known as “one-eighth UL” receivers, and there can be up to 256
of these devices on a network while still complying with the
RS-485 loading specification.
Receiver inputs function with common mode voltages (CMV) of
±2V with V_CC = 1.8V, and with CMVs of -7V to +12V for
V_CC ≥ 2.7V.
All the receivers include a “failsafe-if-open” function that
guarantees a high level receiver output if the receiver inputs are
unconnected (floating). As mentioned previously, the full-failsafe
function is not implemented in order to deliver output duty cycles
that better match the input.
Receivers support data rates up to 256kbps (V_CC = 1.8V) or
500kbps (V_CC ≥ 3V), and receiver outputs of the ISL32611E and
ISL32612E are three-statable via the active low RE or active high
RE input.
Data Rate Recommendations
When coupled with the ISL32613E or ISL32614E 1.8V
transmitter ICs, these receivers are useful for networks up to
4000’ (1220m) long, or for data rates up to 500kbps. For 4000’
distances with V_CC = 1.8V, the ISL32613E can be used with any
of these receivers at data rates ≤ 50kbps. With V_CC = 3.3V, any
transmitter / receiver combination operates over 4000’ at rates
up to 128kbps. Shorter networks allow data rates up to 500kbps,
as shown in Figures 9, 10, 11 and 12.
Network termination resistors are only recommended for
networks operating at V_CC ≥ 2.7V, and using termination
resistors may allow for higher data rates.
Low Power Shutdown Mode (ISL32611E and
ISL32612E)
These devices use a fraction of the power required by most
differential receivers (see Figure 1 on page 1), but they also
include a shutdown feature that reduces the already low
quiescent I_CC even further. The ISL32611E and ISL32612E enter
shutdown whenever the receiver is disabled (RE = GND or
RE = V_CC).
ESD Protection
All pins on these devices include class 3 (>6kV) Human Body
Model (HBM) ESD protection structures, but the bus pins (Rx
inputs) incorporate advanced structures allowing them to survive
ESD events in excess of ±16.5kV HBM and ±16.5kV IEC61000.
The bus pins are particularly vulnerable to ESD damage 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 common mode
range. 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
bus 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 smaller value 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 bus pins allows the design of equipment
meeting level 4 criteria without the need for additional
board-level protection on the I/O port.
AIR-GAP DISCHARGE TEST METHOD
For the air-gap discharge 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 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
ISL32610E, ISL32611E, ISL32612E survive ±9kV contact
discharges on the bus pins.
7
FN7869.0
October 21, 2011