MAX3088CSA Просмотр технического описания (PDF) - Maxim Integrated

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MAX3088CSA

Fail-Safe, High-Speed (10Mbps), Slew-Rate-Limited RS-485/RS-422 Transceivers

Maxim Integrated 

Fail-Safe, High-Speed (10Mbps),

Slew-Rate-Limited RS-485/RS-422 Transceivers

RO

R

RE

DE

DI

D

MAX3080/MAX3081/MAX3083/

MAX3084/MAX3086/MAX3087/

MAX3089 (FULL DUPLEX)

A

120Ω

B

DATA IN

Z

120Ω

Y

DATA OUT

DI

VA - VB

RO

MAX3080/3089 FIG-18

5V/div

1V/div

5V/div

NOTE: RE AND DE ON MAX3080/MAX3083/MAX3086/MAX3089 ONLY.

Figure 17. Line Repeater for MAX3080/MAX3081/MAX3083/

MAX3084/MAX3086/MAX3087, and MAX3089

in Full-Duplex Mode

5µs/div

Figure 18. MAX3080/MAX3081/MAX3082, and MAX3089

with SRL = Unconnected, System Differential Voltage at 50kHz

Driving 4000 feet of Cable

Low-Power Shutdown Mode

(Except MAX3082/MAX3085/MAX3088)

Low-power shutdown mode is initiated by bringing both

RE high and DE low. In shutdown, the devices typically

draw only 1nA of supply current.

RE and DE may be driven simultaneously; the parts are

guaranteed not to enter shutdown if RE is high and DE

is low for less than 50ns. If the inputs are in this state

for at least 600ns, the parts are guaranteed to enter

shutdown.

Enable times tZH and tZL in the Switching Char-

acteristics tables assume the part was not in a low-

power shutdown state. Enable times tZH(SHDN) and

tZL(SHDN) assume the parts were shut down. It takes

drivers and receivers longer to become enabled from

low-power shutdown mode (tZH(SHDN), tZH(SHDN)) than

from driver/receiver-disable mode (tZH, tZL).

Driver Output Protection

Two mechanisms prevent excessive output current and

power dissipation caused by faults or by bus con-

tention. The first, a foldback current limit on the output

stage, provides immediate protection against short cir-

cuits over the whole common-mode voltage range (see

Typical Operating Characteristics). The second, a ther-

mal shutdown circuit, forces the driver outputs into a

high-impedance state if the die temperature becomes

excessive.

Line Length vs. Data Rate

The RS-485/RS-422 standard covers line lengths up to

4000 feet. For line lengths greater than 4000 feet, use

the repeater application shown in Figure 17.

Figures 18, 19, and 20 show the system differential volt-

age for the parts driving 4000 feet of 26AWG twisted-

pair wire at 110kHz into 120Ω loads.

Typical Applications

The MAX3082/MAX3085/MAX3088/MAX3089 trans-

ceivers are designed for bidirectional data communica-

tions on multipoint bus transmission lines. Figures 21

and 22 show typical network applications circuits.

These parts can also be used as line repeaters, with

cable lengths longer than 4000 feet, as shown in Figure 17.

To minimize reflections, the line should be terminated at

both ends in its characteristic impedance, and stub

lengths off the main line should be kept as short as

possible. The slew-rate-limited MAX3082/MAX3085,

and the two modes of the MAX3089, are more tolerant

of imperfect termination.

18 ______________________________________________________________________________________

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