3.3V-Powered, 10Mbps and Slew-Rate-Limited
True RS-485/RS-422 Transceivers
____________________Function Tables
Devices with Receiver/Driver Enable
(MAX3483/MAX3485/MAX3486/MAX3491)
__________Applications Information
The MAX3483/MAX3485/MAX3486/MAX3488/MAX3490/
MAX3491 are low-power transceivers for RS-485 and
RS-422 communications. The MAX3483 and MAX3488
can transmit and receive at data rates up to 250kbps,
the MAX3486 at up to 2.5Mbps, and the MAX3485/
MAX3490/MAX3491 at up to 10Mbps. The MAX3488/
MAX3490/MAX3491 are full-duplex transceivers, while
the MAX3483/MAX3485/MAX3486 are half-duplex.
Driver Enable (DE) and Receiver Enable (RE) pins are
included on the MAX3483/MAX3485/MAX3486/
MAX3491. When disabled, the driver and receiver out-
puts are high impedance.
MAX3483/MAX3485/MAX3486/MAX3488/MAX3490/MAX3491
Table 1. Transmitting
INPUTS
RE
X
X
0
1
DE
1
1
0
0
DI
1
0
X
X
OUTPUTS
B*
0
1
High-Z
High-Z
A*
1
0
High-Z
High-Z
MODE
Normal
Normal
Normal
Shutdown
* B and A outputs are Z and Y, respectively, for full-duplex part
(MAX3491).
X = Don’t care; High-Z = High impedance
Reduced EMI and Reflections
(MAX3483/MAX3486/MAX3488)
The MAX3483/MAX3488 are slew-rate limited, minimiz-
ing EMI and reducing reflections caused by improperly
terminated cables. Figure 13 shows both the driver
output waveform of a MAX3485/MAX3490/MAX3491
transmitting a 125kHz signal and the Fourier analysis of
that waveform. High-frequency harmonics with large
amplitudes are evident. Figure 14 shows the same infor-
mation, but for the slew-rate-limited MAX3483/MAX3488
transmitting the same signal. The high-frequency har-
monics have much lower amplitudes, and the potential for
EMI is significantly reduced.
Table 2. Receiving
INPUTS
RE
0
0
0
1
DE
0*
0*
0*
0
A, B
≥
+0.2V
≤
-0.2V
Inputs Open
X
OUTPUTS
RO
1
0
1
High-Z
MODE
Normal
Normal
Normal
Shutdown
* DE is a “don’t care” (x) for the full-duplex part (MAX3491).
X = Don’t care; High-Z = High impedance
Devices without Receiver/Driver Enable
(MAX3488/MAX3490)
Low-Power Shutdown Mode
(MAX3483/MAX3485/MAX3486/MAX3491)
A low-power shutdown mode is initiated by bringing both
RE high and DE low. The devices will not shut down
unless both the driver and receiver are disabled (high
impedance). In shutdown, the devices typically draw
only 2nA of supply current.
For these devices, the t
PSH
and t
PSL
enable times
assume the part was in the low-power shutdown mode;
the t
PZH
and t
PZL
enable times assume the receiver or
driver was disabled, but the part was not shut down.
Table 3. Transmitting
INPUT
DI
1
0
OUTPUTS
Z
0
1
Y
1
0
Table 4. Receiving
INPUTS
A, B
≥
+0.2V
≤
-0.2V
Inputs Open
OUTPUT
RO
1
0
1
10dB/div
10dB/div
0Hz
500kHz/div
5MHz
0Hz
500kHz/div
5MHz
Figure 13. Driver Output Waveform and FFT Plot of MAX3485/
MAX3490/MAX3491 Transmitting a 125kHz Signal
Figure 14. Driver Output Waveform and FFT Plot of MAX3483/
MAX3488 Transmitting a 125kHz Signal
11
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