20µA,
1
⁄
8
-Unit-Load, Slew-Rate-Limited
RS-485 Transceivers
MAX1482/MAX1483
A
B
500mV/div
500mV/div
B
RO
5V/div
A
5V/div
RO
500ns/div
500ns/div
Figure 11. Receiver t
PHL
Figure 12. Receiver t
PLH
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.
For the receiver, the t
ZH
and t
ZL
enable times assume
the part was not in the low-power shutdown state. The
t
ZH(SHDN)
and t
ZL(SHDN)
enable times assume the
parts were shut down (see
Electrical Characteristics).
It takes the receivers longer to become enabled from
the low-power shutdown state (t
ZH(SHDN)
, t
ZL(SHDN)
)
than from the operating mode (t
ZH
, t
ZL
). (The parts are
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.
The difference in receiver delay times, | t
PLH
- t
PHL
|, is
typically under 160ns.
The driver skew times are typically 160ns (800ns max).
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9
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
