Low-Power Shutdown Mode

(MAX481/MAX483/MAX487)

A low-power shutdown mode is initiated by bringing

both RE high and DE low. The devices will not shut

down unless both the driver and receiver are disabled.

In shutdown, the devices typically draw only 0.1µA 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.

power shutdown state (the MAX485/MAX488–MAX491

down (see Electrical Characteristics).

It takes the drivers and receivers longer to become

enabled from the low-power shutdown state

–

R

—

E

–

,

DE inputs equal a logical 0,1 or 1,1 or 0, 0.)

Driver Output Protection

Excessive output current and power dissipation caused

by faults or by bus contention are prevented by two

mechanisms. 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). In addition, a ther-

mal shutdown circuit forces the driver outputs into a

high-impedance state if the die temperature rises

excessively.

Propagation Delay

Many digital encoding schemes depend on the differ-

ence between the driver and receiver propagation

delay times. Typical propagation delays are shown in

Figures 15–18 using Figure 14’s test circuit.

typically under 13ns for the MAX481, MAX485,

MAX490, MAX491, and MAX1487 and is typically less

than 100ns for the MAX483 and MAX487–MAX489.

The driver skew times are typically 5ns (10ns max) for

the MAX481, MAX485, MAX490, MAX491, and

MAX1487, and are typically 100ns (800ns max) for the

MAX483 and MAX487–MAX489.

Low-Power, Slew-Rate-Limited

RS-485/RS-422 Transceivers

______________________________________________________________________________________

11

10dB/div

0Hz

5MHz

500kHz/div

10dB/div

0Hz

5MHz

500kHz/div

Figure 12. Driver Output Waveform and FFT Plot of MAX481/

MAX485/MAX490/MAX491/MAX1487 Transmitting a 150kHz

Signal

Figure 13. Driver Output Waveform and FFT Plot of MAX483/

MAX487–MAX489 Transmitting a 150kHz Signal