MAX3085EESA Maxim Integrated Products, MAX3085EESA Datasheet - Page 18

• Manufacturer Part Number: MAX3085EESA
• Description: RS-422/RS-485 Interface IC
• Manufacturer: Maxim Integrated Products

Specifications of MAX3085EESA

• Lead Free Status / Rohs Status: No

The standard RS-485 receiver input impedance is 12kΩ
(one-unit load), and the standard driver can drive up to
32 unit loads. The MAX3080E family of transceivers
have a 1/8-unit-load receiver input impedance (96kΩ),
allowing up to 256 transceivers to be connected in par-
allel on one communication line. Any combination of
these devices and/or other RS-485 transceivers with a
total of 32 unit loads or less can be connected to the
line.
The MAX3080E–MAX3085E, and MAX3089E with SRL =
V
EMI and reducing reflections caused by improperly ter-
minated cables. Figure 15 shows the driver output
waveform and its Fourier analysis of a 20kHz signal
transmitted by a MAX3086E/MAX3087E/MAX3088E,
and MAX3089E with SRL = GND. High-frequency har-
monic components with large amplitudes are evident.
Figure 16 shows the same signal displayed for a
MAX3083E/MAX3084E/MAX3085E, and MAX3089E with
SRL = V
Figure 16’s high-frequency harmonic components are
much lower in amplitude, compared with Figure 15’s,
and the potential for EMI is significantly reduced. Figure
17 shows the same signal displayed for a MAX3080E/
MAX3081E/MAX3082E, and MAX3089E with SRL =
unconnected, transmitting under the same conditions.
Figure 17’s high-frequency harmonic components are
even lower.
±15kV ESD-Protected, Fail-Safe, High-Speed (10Mbps),
Slew-Rate-Limited RS-485/RS-422 Transceivers
18
Figure 18. Line Repeater for MAX3080E/MAX3081E/MAX3083E/
MAX3084E/MAX3086E/MAX3087E, and MAX3089E in Full-Duplex
Mode
NOTE: RE AND DE ON MAX3080E/MAX3083E/MAX3086E/MAX3089E ONLY.
CC
or unconnected, are slew-rate limited, minimizing
______________________________________________________________________________________
CC
RO
RE
DE
DI
, transmitting under the same conditions.
D
Applications Information
R
Reduced EMI and Reflections
256 Transceivers on the Bus
A
B
Z
Y
MAX3080E/MAX3081E/MAX3083E/
MAX3084E/MAX3086E/MAX3087E/
120Ω
120Ω
MAX3089E (FULL DUPLEX)
DATA IN
DATA OUT
In general, a transmitter’s rise time relates directly to the
length of an unterminated stub, which can be driven with
only minor waveform reflections. The following equation
expresses this relationship conservatively:
where t
For example, the MAX3080E’s rise time is typically
1320ns, which results in excellent waveforms with a stub
length up to 90 feet. A system can work well with longer
unterminated stubs, even with severe reflections, if the
waveform settles out before the UART samples them.
Low-power shutdown mode is initiated by bringing both
RE high and DE low. In shutdown, the devices typically
draw only 1nA 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.
Enable times t
acteristics tables assume the part was not in a low-
power shutdown state. Enable times t
t
drivers and receivers longer to become enabled from
low-power shutdown mode (t
from driver/receiver-disable mode (t
Figure 19. MAX3080E/MAX3081E/MAX3082E, and MAX3089E
with SRL = Unconnected, System Differential Voltage at 50kHz
Driving 4000ft of Cable
ZL(SHDN)
(Except MAX3082E/MAX3085E/MAX3088E)
V
A
- V
RO
DI
RISE
B
assume the parts were shut down. It takes
is the transmitter’s rise time.
Length = t
ZH
Low-Power Shutdown Mode
and t
RISE
5μs/div
ZL
/ (10 x 1.5ns/ft)
ZH(SHDN)
in the Switching Char-
ZH
, t
, t
ZL
MAX3080/3089 FIG-18
ZL(SHDN)
ZH(SHDN)
).
5V/div
1V/div
5V/div
) than
and