Datasheet

X = Don’t care.
X = Don’t care.
Detailed Description
The MAX3440E–MAX3444E fault-protected transceivers
for RS-485/RS-422 and J1708 communication contain
one driver and one receiver. These devices feature fail-
safe circuitry, which guarantees a logic-high receiver out-
put when the receiver inputs are open or shorted, or when
they are connected to a terminated transmission line with
all drivers disabled (see the True Fail-Safe section). All
devices have a hot-swap input structure that prevents
disturbances on the differential signal lines when a cir-
cuit board is plugged into a hot backplane (see the Hot-
Swap Capability section). The MAX3440E/MAX3442E/
MAX3444E feature a reduced slew-rate driver that mini-
mizes EMI and reduces reflections caused by improperly
terminated cables, allowing error-free data transmission
up to 250kbps (see the Reduced EMI and Reflections
section). The MAX3441E/ MAX3443E drivers are not
slew-rate limited, allowing transmit speeds up to 10Mbps.
Driver
The driver accepts a single-ended, logic-level input (DI)
and transfers it to a differential, RS-485/RS-422 level
output (A and B). Deasserting the driver enable places
the driver outputs (A and B) into a high-impedance state.
Receiver
The receiver accepts a differential, RS-485/RS-422 level
input (A and B), and transfers it to a single-ended, log-
ic-level output (RO). Deasserting the receiver enable
places the receiver inputs (A and B) into a high-imped-
ance state (see Tables 1–7).
Low-Power Shutdown (MAX3442E/MAX3443E/
MAX3444E)
The MAX3442E/MAX3443E/MAX3444E offer a low-
power shutdown mode. Force DE low and RE high to
shut down the MAX3442E/MAX3443E. Force DE and RE
high to shut down the MAX3444E. A time delay of 50ns
prevents the device from accidentally entering shutdown
due to logic skews when switching between transmit and
receive modes. Holding DE low and RE high for at least
800ns guarantees that the MAX3442E/MAX3443E enter
shutdown. In shutdown, the devices consume a maximum
20µA supply current.
±60V Fault Protection
The driver outputs/receiver inputs of RS-485 devices in
industrial network applications often experience voltage
faults resulting from shorts to the power grid that exceed
the -7V to +12V range specified in the EIA/TIA-485 stan-
dard. In these applications, ordinary RS-485 devices
(typical absolute maximum -8V to +12.5V) require costly
external protection devices. To reduce system complexity
and eliminate this need for external protection, the driver
outputs/receiver inputs of the MAX3440E–MAX3444E
withstand voltage faults up to ±60V with respect to ground
without damage. Protection is guaranteed regardless
whether the device is active, shut down, or without power.
True Fail-Safe
The MAX3440E–MAX3444E use a -50mV to -200mV
differential input threshold to ensure true fail-safe receiver
inputs. This threshold guarantees the receiver outputs a
logic-high for shorted, open, or idle data lines. The -50mV
to -200mV threshold complies with the ±200mV threshold
EIA/TIA-485 standard.
Table 7. MAX3444E (RS-485/RS-422)
Table 6. MAX3442E/MAX3443E
(RS-485/RS-422)
RECEIVING
INPUTS OUTPUTS
RE DE (A - B) RO
0 X ≥-0.05V 1
0 X £-0.2V 0
0 X Open/shorted 1
1 0 X High-Z
1 1 X Shutdown
RECEIVING
INPUTS OUTPUTS
RE DE (A - B) RO
0 X ≥-0.05V 1
0 X ≤-0.2V 0
0 X Open/shorted 1
1 1 X High-Z
1 0 X Shutdown
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Maxim Integrated │ 12
MAX3440E–MAX3444E ±15kV ESD-Protected, ±60V Fault-Protected,
10Mbps, Fail-Safe RS-485/J1708 Transceivers
Function Tables (continued)