MAX13085EEPA Datasheet, PDF (12/14 Pages) Maxim Integrated Products – +5.0V, +15,-15kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver

+5.0V, ±15kV ESD-Protected, Fail-Safe,
Hot-Swap, RS-485/RS-422 Transceiver
RC
50MΩ TO 100MΩ
RD
330Ω
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
I
100%
90%
HIGH-
DEVICE
VOLTAGE
Cs
STORAGE
UNDER
DC
150pF
CAPACITOR
TEST
SOURCE
10%
t_r = 0.7ns TO 1ns
30ns
t
60ns
Figure 10c. IEC 61000-4-2 ESD Test Model
Figure 10d. IEC 61000-4-2 ESD Generator Current Waveform
Applications Information
The standard RS-485 receiver input impedance is 12kΩ
(1-unit load), and the standard driver can drive up
to 32-unit loads. The MAX13085E has a 1/8-unit load
receiver input impedance (96kΩ), allowing up to 256
transceivers to be connected in parallel on one commu-
nication line. Any combination of the MAX13085E, as well
as other RS-485 transceivers with a total of 32-unit loads
or fewer, can be connected to the line.
Reduced EMI and Reflections
The MAX13085E features reduced slew-rate drivers that
minimize EMI and reduce reflections caused by improp-
erly terminated cables, allowing error-free data transmis-
sion up to 500kbps.
Low-Power Shutdown Mode
Low-power shutdown mode is initiated by bringing both
RE high and DE low. In shutdown, the devices typically
draw only 2.8μA of supply current.
RE and DE can be driven simultaneously; the devices
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 700ns, the devices are guaranteed to enter
shutdown.
Enable times tZH and tZL (see the Switching
Characteristics section) assume the devices were not in
a low-power shutdown state. Enable times tZH(SHDN) and
tZL(SHDN) assume the devices were in shutdown state.
It takes drivers and receivers longer to become enabled
from low-power shutdown mode (tZH(SHDN), tZL(SHDN))
than from driver/receiver-disable mode (tZH, tZL).
Driver Output Protection
Two mechanisms prevent excessive output current and
power dissipation caused by faults or by bus conten-
tion. The first, a foldback current limit on the output
stage, provides immediate protection against short cir-
cuits over the whole common-mode voltage range (see
the Typical Operating Characteristics). The second, a
thermal-shutdown circuit, forces the driver outputs into
a high-impedance state if the die temperature exceeds
+175°C (typ).
Line Length
The RS-485/RS-422 standard covers line lengths up to
4000ft. For line lengths greater than 4000ft, it may be
necessary to implement a line repeater.
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