20µA,
1
⁄
8
-Unit-Load, Slew-Rate-Limited
RS-485 Transceivers
MAX1482/MAX1483
100pF
Z
TTL IN
t
R
, t
F
< 6ns
D
Y
10dB/div
100pF
R = 54Ω
A
B
R
RECEIVER
OUT
0Hz
500kHz/div
5MHz
Figure 9. Driver Output Waveform and FFT, Transmitting
250kbps (125kHz) Signal
Figure 10. Receiver Propagation-Delay Test Circuit
Table 1. Transmitting
INPUTS
RE
X
X
X
DE
1
1
0
DI
1
0
X
Z
0
1
High-Z
OUTPUTS
Y
1
0
High-Z
Table 2. Receiving
INPUTS
RE
0
0
0
1
DE
*
0
0
0
0
A-B
> +0.2V
< -0.2V
Inputs open
X
OUTPUT
RO
1
0
1
High-Z
X = Don't Care
High-Z = High Impedance
X = Don't Care
High-Z = High Impedance
*
DE = 0 for MAX1483 and is a Don't Care for MAX1482.
__________Applications Information
The MAX1482/MAX1483 are low-power transceivers for
RS-485 and RS-422 communications. The MAX1482
and MAX1483 are specified for data rates of at least
250kbps. The MAX1482 is a full-duplex transceiver
while the MAX1483 is half duplex. When disabled, the
driver and receiver outputs are high impedance.
The 96kΩ,
1
/
8
-unit-load receiver input impedance of the
MAX1482/MAX1483 allows up to 256 transceivers on a
bus, compared to the 1-unit load (12kΩ input imped-
ance) of standard RS-485 drivers (32 transceivers max-
imum). Any combination of MAX1482/MAX1483 and
other RS-485 transceivers with a total of 32 unit loads or
less can be put on the bus.
Reduced EMI and Reflections
The MAX1482/MAX1483 are slew-rate limited, minimiz-
ing EMI and reducing reflections caused by improperly
terminated cables. Figure 9 shows both the driver out-
put waveform of a MAX1482/MAX1483 transmitting a
125kHz signal and the Fourier analysis of that signal.
High-frequency harmonics have much lower ampli-
tudes, and the potential for EMI is significantly reduced.
8
_______________________________________________________________________________________
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