Datasheet

Low-Power, Slew-Rate-Limited
RS-485/RS-422 Transceivers
Maxim Integrated 9
MAX481/MAX483/MAX485/
MAX487–MAX491/MAX1487
MAX483/MAX487/MAX488/MAX489:
Reduced EMI and Reflections
The MAX483 and MAX487–MAX489 are slew-rate limit-
ed, minimizing EMI and reducing reflections caused by
improperly terminated cables. Figure 12 shows the dri-
ver output waveform and its Fourier analysis of a
150kHz signal transmitted by a MAX481, MAX485,
MAX490, MAX491, or MAX1487. High-frequency har-
monics with large amplitudes are evident. Figure 13
shows the same information displayed for a MAX483,
MAX487, MAX488, or MAX489 transmitting under the
same conditions. Figure 13’s high-frequency harmonics
have much lower amplitudes, and the potential for EMI
is significantly reduced.
R
R
Y
Z
V
OD
V
OC
RECEIVER
OUTPUT
TEST POINT
1kΩ
1kΩ
S1
S2
V
CC
C
RL
15pF
DI
DE
3V
Y
Z
C
L1
C
L2
A
B
RO
RE
R
DIFF
V
ID
OUTPUT
UNDER TEST
500Ω
S1
S2
V
CC
C
L
_________________________________________________________________Test Circuits
Figure 4. Driver DC Test Load Figure 5. Receiver Timing Test Load
Figure 6. Driver/Receiver Timing Test Circuit Figure 7. Driver Timing Test Load