ISL3179E 查看數據表（PDF） - Renesas Electronics

零件编号

产品描述 (功能)

生产厂家

ISL3179E

High ESD Protected, +125°C, 40Mbps, 3.3V, Full Fail-Safe RS-485/RS-422 Transceivers

Renesas Electronics 

ISL3179E, ISL3180E

Application Information

RS-485 and RS-422 are differential (balanced) data

transmission standards for use in long haul or noisy

environments. RS-422 is a subset of RS-485, so RS-485

transceivers are also RS-422 compliant. RS-422 is a

point-to-multipoint (multidrop) standard, which allows only one

driver and up to 10 receivers on each bus, assuming one unit

load devices. RS-485 is a true multipoint standard, which allows

up to 32 one unit load devices (any mix of drivers and receivers)

on each bus. To allow for multipoint operation, the RS-485

specification requires that drivers must handle bus contention

without sustaining any damage.

Another important advantage of RS-485 is the extended

common-mode range (CMR), which specifies that the driver

outputs and receiver inputs withstand signals that range from

+12V to -7V. RS-422 and RS-485 are intended for cable lengths

as long as 4000ft (~1200m), so the wide CMR is necessary to

handle ground potential differences, as well as voltages induced

in the cable by external fields.

Receiver (Rx) Features

This transceiver utilizes 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 specifications.

Receiver inputs function with common-mode voltages as great

as +9/-7V outside the power supplies (+12V and -7V), making

them ideal for long networks, or industrial environments, where

induced voltages are a realistic concern.

The receiver input resistance of 50kΩ surpasses the RS-422

specification of 4kΩ, and is five times the RS-485 “Unit Load”

(UL) requirement of 12kΩ minimum. Thus, the ISL3179E is

known as a “one-fifth UL” transceiver, and there can be up to 160

devices on the RS-485 bus while still complying with the RS-485

loading specification.

The receiver is a “full fail-safe” version that guarantees a high

level receiver output if the receiver inputs are unconnected

(floating), shorted together, or connected to a terminated bus

with all the transmitters disabled (terminated/undriven).

Rx outputs deliver large low state currents (typically 28mA at

VOL = 1V) to ease the design of optically coupled isolated

networks.

Receivers easily meet the 40Mbps data rate supported by the

driver, and the receiver output is tri-statable through 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.

Driver outputs are not slew rate limited, so faster output

transition times allow data rates of at least 40Mbps. Driver

outputs are tri-statable through the active high DE input.

FN6365 Rev. 6.00

Nov 9, 2017

For parallel applications, bit-to-bit skews between any two

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 (ISL3179E) or ±12kV HBM (ISL3180E), and

±16.5kV (ISL3179E) or ±4kV (ISL3180E) 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 can 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 (for example, 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 the ISL3179E’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 more difficult to obtain repeatable results. The ISL3179E

RS-485 pins withstand ±16.5kV air-gap discharges, while the

ISL3180E RS-485 pins withstand ±4kV.

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, while the

ISL3180E’s RS-485 pins withstand ±5kV.

Hot Plug Function

When a piece of equipment powers up, a period of time occurs in

which 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 and ISL3180E incorporate a

Page 12 of 18

Share Link: