Complete, Isolated RS-485/RS-422

Data Interface

16

______________________________________________________________________________________

MAX1480B/MAX1480C/MAX1490B:

Reduced EMI and Reflections

The MAX1480B/MAX1480C/MAX1490B are slew-rate-

limited, minimizing EMI and reducing reflections

caused by improperly terminated cables. Figure 11

shows both the driver output waveform of a

MAX1480A/MAX1490A transmitting a 150kHz signal

and the Fourier analysis of that waveform. High-fre-

quency harmonics with large amplitudes are evident.

Figure 12 shows the same information for the slew-rate-

limited MAX1480B/MAX1480C/MAX1490B transmitting

the same signal. The high-frequency harmonics have

much lower amplitudes, and therefore the potential for

EMI is significantly reduced.

Table 3. Transmitting

Table 4. Receiving

Table 5. Transmitting

Table 6. Receiving

1

X

INPUTS*

1

High-Z

OUTPUTS

0

High-Z

1

0

Figure 11. Driver Output Waveform and FFT Plot of

MAX1480A/MAX1490A Transmitting a 150kHz Signal

10dB/div

0Hz

5MHz

500kHz/div

Figure 12. Driver Output Waveform and FFT Plot of

MAX1480B/MAX1480C/MAX1490B Transmitting a 150kHz

Signal

10dB/div

0Hz

5MHz

500kHz/div

_____________________Function Tables

Half-Duplex Devices

(MAX1480A/MAX1480B/MAX1480C)

Full-Duplex Devices

(MAX1490A/MAX1490B)

DI

´

A

B

DE

´

0

0

1

1

≥ +0.2V

Open

INPUTS*

0

0

OUTPUT

(RO)

DE

´

≤ -0.2V

1

0

0

0

0

1

Z

Y

1

0

0

1

1

1

OUTPUT

(RO)

0

≤ -0.2V

≥ +0.2V

Open

INPUT

X = Don’t care

High-Z = High impedance

* For DE

and Typical Application Circuit (Figure 1 for MAX1480A/B/C,

Figure 2 for MAX1490A/B).

OUTPUTS

INPUT

*

(DI