3 .3 V-P o w e re d , 1 0 Mb p s a n d S le w -Ra t e -Lim it e d
Tru e RS -4 8 5 /RS -4 2 2 Tra n s c e ive rs
5680/MAX3491
____________________Fu n c t io n Ta b le s
__________Ap p lic a t io n s In fo rm a t io n
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 a re ha lf-d up le x.
Driver Enable (DE) and Receiver Enable (RE) pins are
inc lud e d on the MAX3483/MAX3485/MAX3486/
MAX3491. When disabled, the driver and receiver out-
puts are high impedance.
De vic e s w it h Re c e ive r/Drive r En a b le
(MAX3 4 8 3 /MAX3 4 8 5 /MAX3 4 8 6 /MAX3 4 9 1 )
Table 1. Transmitting
INPUTS
OUTPUTS
MODE
RE
X
X
0
DE
1
DI
1
B*
A*
1
0
Normal
Normal
1
0
1
0
0
X
X
High-Z
High-Z
High-Z
High-Z
Normal
1
0
Shutdown
* B and A outputs are Z and Y, respectively, for full-duplex part
(MAX3491).
X = Don’t care; High-Z = High impedance
Re d u c e d EMI a n d Re fle c t io n s
(MAX3 4 8 3 /MAX3 4 8 6 /MAX3 4 8 8 )
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
OUTPUTS
MODE
RE
0
DE
A, B
≥ +0.2V
≤ -0.2V
Inputs Open
X
RO
0*
0*
0*
0
1
Normal
Normal
0
0
1
0
Normal
1
High-Z
Shutdown
* DE is a “don’t care” (x) for the full-duplex part (MAX3491).
X = Don’t care; High-Z = High impedance
Lo w -P o w e r S h u t d o w n Mo d e
(MAX3 4 8 3 /MAX3 4 8 5 /MAX3 4 8 6 /MAX3 4 9 1 )
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.
De vic e s w it h o u t Re c e ive r/Drive r En a b le
(MAX3 4 8 8 /MAX3 4 9 0 )
Table 3. Transmitting Table 4. Receiving
INPUT
OUTPUTS
INPUTS
OUTPUT
DI
1
Z
0
1
Y
1
A, B
RO
1
For the s e d e vic e s , the tPSH a nd tPSL e na b le time s
assume the part was in the low-power shutdown mode;
the tPZH and tPZL enable times assume the receiver or
driver was disabled, but the part was not shut down.
≥ +0.2V
≤ -0.2V
0
0
0
Inputs Open
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
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
