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MAX1486EUB+

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
MAX1481/MAX1484/MAX1485/MAX1486
Software-Selectable, Half-/Full-Duplex, Slew-Rate-Limited,
12Mbps, RS-485/RS-422 Transceivers in µMAX Package
10 ______________________________________________________________________________________
_______________Detailed Description
The MAX1481/MAX1484/MAX1485/MAX1486 high-
speed transceivers for RS-485/RS-422 communication
contain one driver and one receiver. The MAX1481/
MAX1485 feature reduced-slew-rate drivers that mini-
mize EMI and reduce reflections caused by improperly
terminated cables, allowing error-free data transmission
up to 250kbps. The MAX1484/MAX1486 driver slew
rates are not limited, making transmission speeds up to
12Mbps possible.
These transceivers are designed to operate on a +5V
single supply and typically draw 300µA of supply cur-
rent when unloaded or fully loaded with the drivers dis-
abled. The MAX1481 has a shutdown mode in which
supply current is typically reduced to 0.1µA.
Drivers are output short-circuit current limited and are
protected against excessive power dissipation by ther-
mal-shutdown circuitry that places the driver outputs
into a high-impedance state.
All devices have a 1/8-unit-load receiver input imped-
ance that allows up to 256 transceivers on the bus. The
MAX1481/MAX1484 are designed for full-duplex com-
munications. The H/F pin on the MAX1485/MAX1486
allows the user to select between half-duplex or full-
duplex operation (Figure 4).
MAX1485/MAX1486
Half-/Full-Duplex Mode Operation
The MAX1484/MAX1485 can operate in full- or half-
duplex mode. Drive the H/F pin low or connect it to
GND for full-duplex operation, or drive it high for half-
duplex operation. In full-duplex mode, the pin configu-
ration of the driver and receiver is the same as a
MAX1481 (Figure 1).
__________Applications Information
256 Transceivers on the Bus
The standard RS-485 receiver input impedance is 12kΩ
(1-unit load), and the standard driver can drive up to
32-unit loads. The MAX1481/MAX1484/MAX1485/
MAX1486 transceivers have a 1/8-unit-load receiver
input impedance (96kΩ), allowing up to 256 trans-
ceivers to be connected in parallel on one communica-
tion line. Connect any combination of these devices
and/or other RS-485 transceivers totaling 32-unit loads
or less.
Reduced EMI and Reflections
The MAX1481/MAX1485 are slew-rate limited, minimiz-
ing EMI and reducing reflections caused by improperly
terminated cables. Figure 14 shows the driver output
waveform and its Fourier analysis of a 20kHz signal
transmitted by a MAX1484. High-frequency harmonic
components with large amplitudes are evident. Figure
15 shows the same signal displayed for a MAX1481
transmitting under the same conditions. Figure 15’s
high-frequency harmonic components are much lower
in amplitude compared to Figure 14’s, significantly
reducing potential EMI.
In general, a transmitter’s rise time relates directly to
the length of an unterminated stub, which can be dri-
ven with only minor waveform reflections. The following
equation expresses this relationship conservatively:
Length = t
RISE
/ (10 x 1.5ns/ft)
where t
RISE
is the transmitter’s rise time.
For example, the MAX1481’s rise time is typically
500ns, which results in excellent waveforms with a stub
length up to 33 feet. A system may work well with
longer unterminated stubs, even with severe reflec-
tions, if the waveform settles out before the UART
samples them.
Figure 4. MAX1485/MAX1486 Functional Diagram
MAX1485
MAX1486
Z
DI
DE
RO
V
CC
GND
Y
B
A
H/F
MAX1481/MAX1484/MAX1485/MAX1486
Software-Selectable, Half-/Full-Duplex, Slew-Rate-Limited,
12Mbps, RS-485/RS-422 Transceivers in µMAX Package
______________________________________________________________________________________ 11
R
R
Y
Z
V
OD
V
OC
Figure 5. Driver DC Test Load
RECEIVER
OUTPUT
TEST POINT
1k
1k
S1
S2
V
CC
C
L
Figure 6. Receiver Enable/Disable Timing Test Load
DI
DE
3V
Y
Z
C
L1
C
L2
R
DIFF
V
ID
Figure 7. Driver Timing Test Circuit
OUTPUT
UNDER TEST
500Ω
S1
S2
V
CC
C
L
Figure 8. Driver Enable/Disable Timing Test Load
DI
3V
0V
Z
Y
V
O
0V
-V
O
V
O
1.5V
t
DPLH
1/2 V
O
10%
t
R
90%
90%
t
DPHL
1.5V
1/2 V
O
10%
t
F
V
DIFF
= V
Y
- V
Z
V
DIFF
t
SKEW = |
t
PLH
- t
PHL
|
Figure 9. Driver Propagation Delays
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
3V
0V
Y, Z
V
OL
Y, Z
0V
1.5V 1.5V
V
OL
+0.5V
V
OH
-0.5V
2.3V
2.3V
t
DZL(SHDN)
, t
DPL
t
DLZ
D
ZH(SHDN)
, D
ZH
D
HZ
DE
Figure 10. Driver Enable and Disable Times
MAX1481/MAX1484/MAX1485/MAX1486
Software-Selectable, Half-/Full-Duplex, Slew-Rate-Limited,
12Mbps, RS-485/RS-422 Transceivers in µMAX Package
12 ______________________________________________________________________________________
Low-Power Shutdown Mode
(MAX1481 only)
Low-power shutdown mode is initiated by bringing both
RE high and DE low. In shutdown, the MAX1481 typi-
cally draws only 0.1µA of supply current.
RE and DE may be driven simultaneously; the parts are
guaranteed not to enter shutdown if RE is high and DE
is low for less than 50ns. If the inputs are in this state
for at least 600ns, the parts are guaranteed to enter
shutdown.
Enable times t_
ZH
and t_
Z
L
in the
Switching Character-
istics
tables assume the part was not in low-power shut-
down. Enable times t_
ZH
(SHDN)
and t_
ZL
(SHDN)
assume
the parts were shut down. It takes drivers and receivers
longer to become enabled from the low-power shutdown
mode (t_
ZH
(SHDN)
, t_
Z
L(SHDN)
) than from the
driver/receiver disable mode (t_
ZH
, t_
Z
L
).
Driver Output Protection
Excessive output current and power dissipation caused
by faults or by bus contention are prevented by two
mechanisms. A foldback current limit on the output
stage provides immediate protection against short cir-
cuits over the whole common-mode voltage range (see
Typical Operating Characteristics
). In addition, a ther-
mal shutdown circuit forces the driver outputs into a
high-impedance state if the die temperature becomes
excessive.
V
OH
V
OL
A
B
1V
-1V
1.5V 1.5V
OUTPUT
INPUT
RO
R
PLH
R
PHL
Figure 11. Receiver Propagation Delays
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
3V
0V
V
CC
RO
RO
0V
1.5V 1.5V
V
OL
+ 0.5V
V
OH
- 0.5V
1.5V
1.5V
R
ZL(SHDN)
, R
ZL
R
LZ
R
ZH(SHDN)
, R
ZH
R
HZ
RE
Figure 12. Receiver Enable and Disable Times
(MAX1481/MAX1484 only)
R
B
RECEIVER
OUTPUT
ATE
A
V
ID
R
Figure 13. Receiver Propagation Delay Test Circuit
20dB/div
250kHz/div 2.5MHz0Hz
MAX1481/4/5/6-fig14
Figure 14. Driver Output Waveform and FFT Plot of
MAX1484/MAX1486 Transmitting a 20kHz signal
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

MAX1486EUB+

Mfr. #:
Buy MAX1486EUB+
Manufacturer:
Maxim Integrated
Description:
RS-422/RS-485 Interface IC 12Mbps RS485/RS422 Transceiver
Lifecycle:
New from this manufacturer.
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