Rainbow Electronics MAX3079E - Manual (Page 18)

MAX3070E–MAX3079E
Low-Power Shutdown Mode (Except
MAX3071E/MAX3074E/MAX3077E)
Low-power shutdown mode is initiated by bringing both
RE high and DE low. In shutdown, the devices typically
draw only 50nA of supply current.
RE and DE can 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 t ZH and t ZL (see the Switching
Characteristics section) assume the part was not in a
low-power shutdown state. Enable times t
ZH(SHDN) and
t
ZL(SHDN)
assume the parts were shut down. It takes
drivers and receivers longer to become enabled from
low-power shutdown mode (t
ZH(SHDN) , t ZL(SHDN) ) than
from driver/receiver-disable mode (t
ZH
, t
ZL
).
Driver Output Protection
Two mechanisms prevent excessive output current and
power dissipation caused by faults or by bus contention.
The first, a foldback current limit on the output stage,
provides immediate protection against short circuits over
the whole common-mode voltage range (see the Typical
Operating Characteristics). The second, a thermal-shut-
down circuit, forces the driver outputs into a high-imped-
ance state if the die temperature becomes excessive.
Line Length
The RS-485/RS-422 standard covers line lengths up to
4000ft. For line lengths greater than 4000ft, use the
repeater application shown in Figure 11.
Typical Applications
The MAX3072E/MAX3075E/MAX3078E/MAX3079E
transceivers are designed for bidirectional data commu-
nications on multipoint bus transmission lines. Figures
12 and 13 show typical network applications circuits.
To minimize reflections, terminate the line at both ends
in its characteristic impedance, and keep stub lengths
off the main line as short as possible. The slew-rate-lim-
ited MAX3072E/MAX3075E and the two modes of the
MAX3079E are more tolerant of imperfect termination.
Chip Information
TRANSISTOR COUNT: 1228
PROCESS: BiCMOS
+3.3V, ±15kV ESD-Protected, Fail-Safe,
Hot-Swap, RS-485/RS-422 Transceivers
18 ______________________________________________________________________________________
RO
DI
DE
R
D
MAX3070E/MAX3071E/MAX3073E/
MAX3074E/MAX3076E/MAX3077E/
MAX3079E (FULL-DUPLEX)
RE
120 Ω
120 Ω
A
B
Z
Y
DATA IN
DATA OUT
Figure 11. Line Repeater for MAX3070E/MAX3071E/MAX3073E/
MAX3074E/MAX3076E/MAX3077E/MAX3079E in Full-Duplex
Mode
DI RO DE
A
B
RE
RO
RO
RO
DI
DI
DI
DE
DE
DE
D D
D
R R
R
B B
B
A A A
120 Ω 120 Ω
D
R
MAX3072E
MAX3075E
MAX3078E
MAX3079E (HALF-DUPLEX) RE RE
RE
Figure 12. Typical Half-Duplex RS-485 Network