Low-Power, Slew-Rate-Limited
RS-485/RS-422 Transceivers
_________________________________________________________________Test Circuits
Y
1kΩ
R
R
TEST POINT
RECEIVER
OUTPUT
V
CC
S1
S2
V
OD
C
RL
1kΩ
15pF
V
OC
Z
Figure 4. Driver DC Test Load
Figure 5. Receiver Timing Test Load
3V
DE
V
CC
S1
S2
C
500Ω
L1
A
OUTPUT
UNDER TEST
Y
R
DIFF
RO
DI
C
L
V
ID
B
Z
RE
C
L2
Figure 6. Driver/Receiver Timing Test Circuit
Figure 7. Driver Timing Test Load
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.
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-
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9
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
