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.

Low-Power, Slew-Rate-Limited

RS-485/RS-422 Transceivers

_______________________________________________________________________________________

9

R

R

Y

Z

RECEIVER

OUTPUT

TEST POINT

1kΩ

1kΩ

S1

S2

15pF

DI

DE

3V

Y

Z

A

B

RO

RE

OUTPUT

UNDER TEST

500Ω

S1

S2

_________________________________________________________________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