ISL83088EIU-T【PDF 4/19 页】IC TXRX RS485/422 5V ESD 8-MSOP

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Sheet目录2002

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FN6085.9

April 22, 2008

115kbps versions 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 120

Ω) 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 transceiver to

the main cable should be kept as short as possible.

Built-In Driver Overload Protection

As stated previously, the RS-485 specification requires that

drivers survive worst case bus contentions undamaged.

These devices meet this requirement via driver output short

circuit current limits, and on-chip thermal shutdown circuitry.

The driver output stages incorporate short circuit current

limiting circuitry which ensures that the output current never

exceeds the RS-485 specification, even at the common

mode voltage range extremes. Additionally, these devices

utilize a foldback circuit which reduces the short circuit

current, and thus the power dissipation, whenever the

contending voltage exceeds either supply.

In the event of a major short circuit condition, devices also

include a thermal shutdown feature that disables the drivers

whenever the die temperature becomes excessive. This

eliminates the power dissipation, allowing the die to cool. The

drivers automatically re-enable after the die temperature

drops about +15°C. If the contention persists, the thermal

shutdown/re-enable cycle repeats until the fault is cleared.

Receivers stay operational during thermal shutdown.

Low Power Shutdown Mode

These CMOS transceivers all use a fraction of the power

required by their bipolar counterparts, but they also include a

shutdown feature (except for the ISL83084E) that reduces

the already low quiescent ICC to a 70nA trickle. These

devices enter shutdown whenever the receiver and driver

are simultaneously disabled (RE =VCC and DE = GND) for

a period of at least 600ns. Disabling both the driver and the

receiver for less than 60ns guarantees that the transceiver

will not enter shutdown.

Note that receiver and driver enable times increase when

the transceiver enables from shutdown. Refer to Notes 8

thru 12, at the end of the “Electrical Specification Table” on

page 8, for more information.

Typical Performance Curves VCC = 5V, TA = +25°C; Unless Otherwise Specified

FIGURE 8. DRIVER OUTPUT CURRENT vs DIFFERENTIAL

OUTPUT VOLTAGE

FIGURE 9. DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs

TEMPERATURE

DIFFERENTIAL OUTPUT VOLTAGE (V)

DRIVER

OUTPUT

CUR

(mA)

01234

-40

TEMPERATURE (°C)

IFFERENTIAL

OUTPUT

VOL

AGE

(V)

-25

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

RDIFF = 54Ω

RDIFF = 100Ω

ISL83080E, ISL83082E, ISL83083E, ISL83084E, ISL83085E, ISL83086E, ISL83088E

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