MAX13485E Datasheet, PDF (14/16 Pages) Maxim Integrated Products – Half-Duplex RS-485/RS-422 Transceivers in uDFN

Half-Duplex RS-485/RS-422 Transceivers in µDFN
DI
D
R_t
DE
RO
R
RE
R_t
D
DI
DE
R
RO
RE
MAX13485E
MAX13486E
R
D
R
D
DI DE RO RE
Figure 11. Typical Half-Duplex RS-485 Network
DI DE RO RE
withstand voltage measured to IEC 61000-4-2 is gener-
ally lower than that measured using the Human Body
Model. Figure 10c shows the IEC 61000-4-2 model,
and Figure 10d shows the current waveform for the IEC
61000-4-2 ESD Contact Discharge test.
Machine Model
The machine model for ESD tests all pins using a 200pF
storage capacitor and zero discharge resistance.
The objective is to emulate the stress caused when I/O
pins are contacted by handling equipment during test
and assembly. Of course, all pins require this protec-
tion, not just RS-485 inputs and outputs.
The air-gap test involves approaching the device with a
charged probe. The contact-discharge method connects
the probe to the device before the probe is energized.
Applications Information
128 Transceivers on the Bus
The standard RS-485 receiver input impedance is 12kΩ
(1-unit load), and the standard driver can drive up to
32-unit loads. The MAX13485E/MAX13486E have a 1/4-
unit load receiver input impedance (48kΩ), allowing up
to 128 transceivers to be connected in parallel on one
communication line. Any combination of these devices,
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 MAX13485E features reduced slew-rate drivers
that minimize EMI and reduce reflections caused by
improperly terminated cables, allowing error-free data
transmission 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 draw a
maximum of 10µA 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 t_ZH and t_ZL (see the Switching Character-
istics) assume the devices were not in a low-power shut-
down state. Enable times t_ZH(SHDN) and t_ZL(SHDN)
assume the devices were in shutdown state. It takes dri-
vers 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).
Line Length
The RS-485/RS-422 standard covers line lengths up to
4000ft.
Typical Applications
The MAX13485E/MAX13486E transceivers are
designed for half-duplex, bidirectional data communi-
cations on multipoint bus transmission lines. Figure 11
shows typical network applications circuits. To mini-
mize 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-limited
MAX13485E is more tolerant of imperfect termination.
PROCESS: BiCMOS
Chip Information
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