±1 5 k V ES D-P ro t e c t e d , S le w -Ra t e -Lim it e d ,
Lo w -P o w e r, RS -4 8 5 /RS -4 2 2 Tra n s c e ive rs
35–9/MAX1487E
delay times. Typical propagation delays are shown in
Figures 19–22 using Figure 18’s test circuit.
The difference in receiver delay times, t
- t
, is
PHL
PLH
typ ic a lly und e r 13ns for the MAX481E, MAX485E,
MAX490E, MAX491E, and MAX1487E, and is typically
le s s tha n 100ns for the MAX483E a nd MAX487E–
MAX489E.
100pF
Z
B
A
TTL IN
t , t < 6ns
RECEIVER
OUT
D
R
R
F
R = 54Ω
Y
The driver skew times are typically 5ns (10ns max) for
the MAX481E, MAX485E, MAX490E, MAX491E, and
MAX1487E, and are typically 100ns (800ns max) for the
MAX483E and MAX487E–MAX489E.
100pF
Typ ic a l Ap p lic a t io n s
The MAX481E, MAX483E, MAX485E, MAX487E–
MAX491E, and MAX1487E transceivers are designed for
bidirectional data communications on multipoint bus
transmission lines. Figures 25 and 26 show typical net-
work application circuits. These parts can also be used as
line repeaters, with cable lengths longer than 4000 feet.
Figure 18. Receiver Propagation Delay Test Circuit
It takes the drivers and receivers longer to become
enabled from the low-power shutdown state (t ),
ZH(SHDN
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 possi-
ble. The slew-rate-limited MAX483E and MAX487E–
MAX489E are more tolerant of imperfect termination.
t
) than from the operating mode (t , t ). (The
ZL(SHDN)
ZH ZL
parts are in operating mode if the RE, DE inputs equal a
logical 0,1 or 1,1 or 0, 0.)
Drive r Ou t p u t P ro t e c t io n
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 circuits over
the whole common-mode voltage range (see Typical
Operating Characteristics). In addition, a thermal shut-
down circuit forces the driver outputs into a high-imped-
ance state if the die temperature rises excessively.
Bypass the V pin with 0.1µF.
CC
Is o la t e d RS -4 8 5
For isolated RS-485 applications, see the MAX253 and
MAX1480 data sheets.
Lin e Le n g t h vs . Da t a Ra t e
The RS-485/RS-422 standard covers line lengths up to
4000 feet. Figures 23 and 24 show the system differen-
tial voltage for the parts driving 4000 feet of 26AWG
twisted-pair wire at 110kHz into 100Ω loads.
P ro p a g a t io n De la y
Many digital encoding schemes depend on the differ-
e nc e b e twe e n the d rive r a nd re c e ive r p rop a g a tion
______________________________________________________________________________________ 13
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
