ISL3280E, ISL3281E, ISL3282E, ISL3283E, ISL3284E, ISL3285E

9

FN6543.4

July 27, 2015

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All the receivers include a “full fail-safe” function that

guarantees a high level receiver output if the receiver inputs are

unconnected (floating), shorted together, or connected to a

terminated but undriven bus. Fail-safe with shorted inputs is

achieved by setting the Rx upper switching point to -50mV,

thereby ensuring that the Rx sees 0V differential as a high input

level.

All receivers easily support a 20Mbps data rate and all receiver

outputs (except on the ISL3280E and ISL3284E) are

tri-statable via the active low RE input or by the active high RE

input.

Wide Supply Range

The ISL3280E, ISL3281E, ISL3282E, ISL3283E, ISL3284E,

ISL3285E are designed to operate with a wide range of

supply voltages from 3.0V to 5.5V. These devices meet the

RS-422 and RS-485 specifications over this full range.

ISL3285E Only)

powers the logic input (RE or RE) and/or the Rx output. These

pins interface with “logic” devices such as UARTs, ASICs and

microcontrollers and today most of these devices use power

supplies significantly lower than 3.3V. Thus, a 3.3V output level

from a 3.3V powered RS-485 IC might seriously overdrive and

damage the logic device input. Similarly, the logic device’s low

device (as shown in Figure 6) limits the ISL3282E, ISL3284E,

and reduces the RE/RE input switching point to a value

compatible with the logic device’s output levels. Tailoring the

logic pin input switching point and output levels to the supply

voltage of the UART, ASIC, or microcontroller eliminates the

need for a level shifter/translator between the two ICs.

switching points may not provide enough noise margin when

ESD Protection

All pins on these devices include class 3 (>4kV) Human Body

Model (HBM) ESD protection structures, but the RS-485 pins

(receiver inputs) incorporate advanced structures allowing

them to survive ESD events in excess of ±16.5kV HBM and

±16.5kV IEC61000. The RS-485 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 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.

(V)

(V)

(V)

DATA RATE

(Mbps)

1.35

0.55

0.5

11

1.6

0.7

0.6

16

1.8

0.8

0.7

23

2.3

1

0.9

27

2.7

1.1

1

30

3.3

1.3

1.2

30

1.8

24

GND

RXEN

UART/PROCESSOR

GND

RO

RE

ISL3283E

ESD

DIODE

GND

RXEN

UART/PROCESSOR

GND

RO

RE

ISL3282E

ESD

DIODE