MAX1480A_05 Datasheet, PDF (16/21 Pages) Maxim Integrated Products – Complete, Isolated RS-485/RS-422 Data Interface

Complete, Isolated RS-485/RS-422
Data Interface
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.
_____________________Function Tables
Half-Duplex Devices
(MAX1480A/MAX1480B/MAX1480C)
Table 3. Transmitting
INPUTS*
DE´
DI´
1
1
1
0
0
X
OUTPUTS
B
A
0
1
1
0
High-Z
High-Z
X = Don’t care
High-Z = High impedance
10dB/div
Table 4. Receiving
INPUTS*
DE´
V_A - V_B
0
≥ +0.2V
0
≤ -0.2V
0
Open
OUTPUT
(RO)
0
1
0
0Hz
5MHz
500kHz/div
Figure 11. Driver Output Waveform and FFT Plot of
MAX1480A/MAX1490A Transmitting a 150kHz Signal
10dB/div
Full-Duplex Devices
(MAX1490A/MAX1490B)
Table 5. Transmitting
INPUT*
(DI´)
OUTPUTS
Z
Y
1
0
1
0
1
0
* For DE´ and DI´ pin descriptions, see Detailed Block Diagram
and Typical Application Circuit (Figure 1 for MAX1480A/B/C,
Figure 2 for MAX1490A/B).
0Hz
5MHz
500kHz/div
Figure 12. Driver Output Waveform and FFT Plot of
MAX1480B/MAX1480C/MAX1490B Transmitting a 150kHz
Signal
Table 6. Receiving
INPUT
(V_A - V_B)
≥ +0.2V
≤ -0.2V
Open
OUTPUT
(RO)
1
0
1
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