3.3V-Pow e re d, ±15kV ESD-Prote c te d, 12Mbps a nd
Sle w -Ra te -Lim ite d True RS -485/RS -422 Tra ns c e ive rs
R
C
R
D
1M
1500Ω
I 100%
P
90%
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
I
r
DISCHARGE
RESISTANCE
CHARGE-CURRENT
LIMIT RESISTOR
AMPERES
HIGH-
VOLTAGE
DC
DEVICE
UNDER
TEST
36.8%
C
100pF
STORAGE
CAPACITOR
s
10%
0
SOURCE
TIME
0
t
RL
t
DL
CURRENT WAVEFORM
Figure 22b. Human Body Current Waveform
Figure 22a. Human Body ESD Test Model
R
R
D
330Ω
C
I
50M to 100M
100%
90%
DISCHARGE
RESISTANCE
CHARGE-CURRENT
LIMIT RESISTOR
HIGH-
VOLTAGE
DC
DEVICE
UNDER
TEST
C
s
150pF
STORAGE
CAPACITOR
SOURCE
10%
Figure 23a. IEC 1000-4-2 ESD Test Model
t
t = 0.7ns to 1ns
r
30ns
60ns
Figure 23b. IEC 1000-4-2 ESD Generator Current Waveform
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.
Typ ic a l Ap p lic a t io n s
The MAX3483E/MAX3485E/MAX3486E/MAX3488E/
MAX3490E/MAX3491E transceivers are designed for
bidirectional data communications on multipoint bus
transmission lines. Figures 24 and 25 show typical net-
work applications circuits. These parts can also be
used as line repeaters, with cable lengths longer than
4000 feet, as shown in Figure 21.
Machine Model
The Ma c hine Mod e l for ESD te s ts a ll p ins us ing a
200pF storage capacitor and zero discharge resis -
tance. Its 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 protection, not just RS-485 inputs and outputs.
To minimize reflections, the line should be terminated at
both ends in its characteristic impedance, and stub
lengths off the main line should be kept as short as
possible. The slew-rate-limited MAX3483E/MAX3488E
and the partially slew-rate-limited MAX3486E are more
tolerant of imperfect termination.
5680/MAX3491E
14 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
