Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
R
1MΩ
R
R
R
C
D
C
D
1500Ω
50MΩ TO 100MΩ
330Ω
DISCHARGE
RESISTANCE
DISCHARGE
RESISTANCE
CHARGE-CURRENT-
LIMIT RESISTOR
CHARGE-CURRENT-
LIMIT RESISTOR
HIGH-
VOLTAGE
DC
HIGH-
VOLTAGE
DC
DEVICE
UNDER
TEST
DEVICE
UNDER
TEST
C
s
150pF
STORAGE
CAPACITOR
C
s
100pF
STORAGE
CAPACITOR
SOURCE
SOURCE
Figure 10c. ICE 61000-4-2 ESD Test Model
Figure 10a. Human Body ESD Test Model
I
100%
90%
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
I
100%
90%
I
P
r
AMPS
36.8%
10%
0
10%
TIME
0
t = 0.7ns TO 1ns
r
t
RL
t
30ns
60ns
t
DL
CURRENT WAVEFORM
Figure 10d. IEC 61000-4-2 ESD Generator Current Waveform
Figure 10b. Human Body Current Waveform
Low-Power Shutdown Mode
Low-power shutdown mode is initiated by bringing
SHDN low. In shutdown, the devices draw a maximum
of 10µA of supply current.
Applications Information
128 Transceivers on the Bus
The standard RS-485 receiver input impedance is 12ꢀΩ
(1-unit load), and the standard driver can drive up to
32-unit loads. The MAX13487E/MAX13488E have a 1/4-
unit load receiver input impedance (48ꢀΩ), 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.
The devices are guaranteed not to enter shutdown if
SHDN 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
and t (see the Switching Character-
ZL
Zꢁ
istics section) assume the devices were not in a low-
power shutdown state. Enable times t and
Zꢁ(SꢁDN)
Reduced EMI and Reflections
The MAX13487E features reduced slew-rate drivers
that minimize EMI and reduce reflections caused by
improperly terminated cables, allowing error-free data
transmission up to 500ꢀbps.
t
assume the devices were in shutdown state. It
ZL(SꢁDN)
taꢀes drivers and receivers longer to become enabled
from low-power shutdown mode (t , t
)
Zꢁ(SꢁDN) ZL(SꢁDN)
than from driver/receiver-disable mode (t , t ).
Zꢁ ZL
Line Length
The RS-485/RS-422 standard covers line lengths up to
4000ft.
14 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
