MAX1482 Maxim, MAX1482 Datasheet - Page 8

• Manufacturer Part Number: MAX1482
• Description: 20A / 1.8-Unit-Load / Slew-Rate-Limited RS-485 Transceivers
• Manufacturer: Maxim

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,
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.
20µA,
RS-485 Transceivers
Figure 9. Driver Output Waveform and FFT, Transmitting
250kbps (125kHz) Signal
Table 1. Transmitting
8
__________Applications Information
X = Don't Care
High-Z = High Impedance
10dB/div
_______________________________________________________________________________________
RE
X
X
X
0Hz
1
/
8
INPUTS
-unit-load receiver input impedance of the
DE
1
1
0
1
⁄
8
-Unit-Load, Slew-Rate-Limited
DI
1
0
X
500kHz/div
High-Z
Z
0
1
OUTPUTS
High-Z
Y
1
0
5MHz
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.
Figure 10. Receiver Propagation-Delay Test Circuit
Table 2. Receiving
X = Don't Care
High-Z = High Impedance
*
DE = 0 for MAX1483 and is a Don't Care for MAX1482.
t
R
RE
, t
0
0
0
1
F
TTL IN
< 6ns
D
INPUTS
Reduced EMI and Reflections
DE
Z
Y
0
0
0
0
*
100pF
100pF
R = 54
Inputs open
> +0.2V
< -0.2V
A-B
X
B
A
R
OUTPUT
High-Z
RO
1
0
1
RECEIVER
OUT