Low-Power, Slew-Rate-Limited
RS-485/RS-422 Transceivers
MAX481/MAX483/MAX485/MAX487–MAX491/MAX1487
_________________________________________________________________Test Circuits
Y
R
V
OD
R
Z
V
OC
S2
TEST POINT
RECEIVER
OUTPUT
C
RL
15pF
1kΩ
V
CC
S1
1kΩ
Figure 4. Driver DC Test Load
Figure 5. Receiver Timing Test Load
3V
DE
DI
Y
V
ID
Z
C
L1
R
DIFF
A
RO
B
RE
500Ω
OUTPUT
UNDER TEST
C
L
S1
V
CC
S2
C
L2
Figure 6. Driver/Receiver Timing Test Circuit
Figure 7. Driver Timing Test Load
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.
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9
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
