ISL32610E, ISL32611E, ISL32612E

7

FN7869.0

October 21, 2011

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

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.

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’

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

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

shutdown whenever the receiver is disabled (RE = GND or

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.