MAX13487E Datasheet, PDF (14/17 Pages) Maxim Integrated Products – Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control

Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
R_C
R_D
1MΩ
1500Ω
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
HIGH-
VOLTAGE
DC
SOURCE
Cs
100pF
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
R_C
50MΩ TO 100MΩ
R_D
330Ω
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
HIGH-
VOLTAGE
DC
SOURCE
Cs
150pF
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
Figure 10a. Human Body ESD Test Model
I_P 100%
90%
Ir
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPS
36.8%
10%
0
0 _tRL
TIME
t_DL
CURRENT WAVEFORM
Figure 10b. Human Body Current Waveform
Figure 10c. ICE 61000-4-2 ESD Test Model
I
100%
90%
10%
tr = 0.7ns TO 1ns
30ns
t
60ns
Figure 10d. IEC 61000-4-2 ESD Generator Current Waveform
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 MAX13487E/MAX13488E 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 MAX13487E 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
SHDN low. In shutdown, the devices draw a maximum
of 10µA of supply current.
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_ZH and t_ZL (see the Switching Character-
istics section) assume the devices were not in a low-
power shutdown state. Enable times t_ZH(SHDN) and
t_ZL(SHDN) assume the devices were in shutdown state. It
takes drivers 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.
14 ______________________________________________________________________________________