Low-Power Shutdown Mode

A low-power shutdown mode is initiated by bringing RE

high and DE low. The devices will not shut down unless

both the driver and receiver are disabled. In shut-

down, 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 shut-

down.

the part was not in the low-power shutdown state. The

parts were shut down (see

Electrical Characteristics).

It takes the receivers longer to become enabled from

in operating mode if the RE , 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

Digital encoding schemes depend on the driver and

receiver skew. Skew is defined as the difference

between the rising and falling propagation delay times.

Typical propagation delays are shown in Figures 11

and 12 using Figure 10’s test circuit.

typically under 160ns.

The driver skew times are typically 160ns (800ns max).

RS-485 Transceivers

_______________________________________________________________________________________

9

RO

5V/div

B

A

500mV/div

500ns/div

RO

5V/div

A

B

500mV/div

500ns/div