MAX3291
更新时间:2024-09-18 02:28:32
品牌:MAXIM
描述:RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication
MAX3291 概述
RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication RS - 485 / RS - 422收发器,带有预加重的高速,长距离通信
MAX3291 数据手册
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PDF下载19-1405; Rev 1; 4/99
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
1/MAX392
________________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
The MAX3291/MAX3292 high-speed RS-485/RS-422
transceivers feature driver preemphasis circuitry, which
extends the distance and increases the data rate of reli-
able communication by reducing intersymbol interfer-
ence (ISI) caused by long cables. The MAX3291 is
programmable for data rates of 5Mbps to 10Mbps,
while the MAX3292 is programmable for data rates up
to 10Mbps by using a single external resistor.
♦ Preemphasis Increases the Distance and Data
Rate of Reliable RS-485/RS-422 Communication
♦ Data Rate
Optimized for 5Mbps to 10Mbps (MAX3291)
Programmable up to 10Mbps (MAX3292)
♦ 100nA Low-Current Shutdown Mode
♦ Allow Up to 128 Transceivers on the Bus
♦ -7V to +12V Common-Mode Input Voltage Range
The MAX3291/MAX3292 are full-duplex devices that
operate from a single +5V supply and offer a low-cur-
rent shutdown mode that reduces supply current to
100nA. They feature driver output short-circuit current
limiting and a fail-safe receiver input that guarantees a
logic-high output if the input is open circuit. A 1/4-unit-
load receiver input impedance allows up to 128 trans-
ceivers on the bus.
♦ Pin-Compatible with ’75180, MAX489, MAX491
MAX3080, MAX3083, MAX3086, MAX1482
_______________Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
14 SO
MAX3291CSD
MAX3291CPD
MAX3291ESD
MAX3291EPD
MAX3292CSD
MAX3292CPD
MAX3292ESD
MAX3292EPD
14 Plastic DIP
14 SO
________________________Ap p lic a t io n s
Long-Distance, High-Speed RS-485/RS-422
Communications
14 Plastic DIP
14 SO
Telecommunications
14 Plastic DIP
14 SO
Industrial-Control Local Area Networks
14 Plastic DIP
Typ ic a l Op e ra t in g Circ u it a n d Fu n c t io n a l Dia g ra m
R
*
R
*
*
PSET
PSET
1µF
1µF
C
PSET
C
PSET
*
PEE
PEE
(PSET)
(PSET)
1
V
CC
V
CC
14
1
14
13
13
(V
CCD
)
(V
)
CCD
12
11
A
R = Z
R = Z
O
9
10
Y
Z
O
2
5
RO
DI
B
4
3
3
4
5
DE
RE
RE
DE
DI
10
R = Z
R = Z
O
Z
11
12
B
A
O
2
RO
Y 9
( ) ARE FOR MAX3292
* MAX3292 ONLY
MAX3291
MAX3292
MAX3291
MAX3292
Z = THE CHARACTERISTIC
O
IMPEDANCE OF THE CABLE
7(6) GND
7(6)
GND
Pin Configuration appears at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V , V
) .................................................+6V
Operating Temperature Ranges
CC CCD
Control Input Voltage (RE, DE, PEE,
PSET, DI) .................................................-0.3V to (V + 0.3V)
Driver Output Voltage (Y, Z)................................-7.5V to +12.5V
Receiver Input Voltage (A, B)..............................-7.5V to +12.5V
MAX329_C_ D......................................................0°C to +70°C
MAX329_E_ D...................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
CC
Receiver Output Voltage (RO)....................-0.3V to (V + 0.3V)
CC
Continuous Power Dissipation (T = +70°C)
A
14-Pin SO (derate 8.7mW/°C above +70°C).................695mW
14-Pin Plastic DIP (derate 10.0mW/°C above +70°C) ..800mW
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(Typical Operating Circuit, V = +5V ±5%, R
= 0 (MAX3292), V = V
(MAX3292), T = T
A
to T , unless otherwise
MAX
CC
PSET
CC
CCD
MIN
noted. Typical values are at V = +5V and T = +25°C.) (Note 1)
CC
A
PARAMETER
DRIVER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
1/MAX392
R = 27Ω
No load (Note 2)
1.5
5.0
Differential Driver Output
V
Figure 1
V
V
V
OD
5.25
Differential Driver Output with
Preemphasis
V
ODP
R = 27Ω
2.4
Differential Driver
Preemphasis Ratio
DPER
Figure 1, R = 27Ω (Note 3)
Figure 1, R = 27Ω (Note 4)
1.65
2.0
2.35
0.2
Change in Magnitude of
Differential Output Voltage
(Normal and Preemphasis)
∆V
,
OD
V
V
V
∆V
ODP
Driver Common-Mode Output
Voltage (Normal and
Preemphasis)
V
OC
Figure 1, R = 27Ω
V
/ 2
3
CC
Change in Magnitude of
Common-Mode Voltage
(Normal and Preemphasis)
∆V
Figure 1, R = 27Ω (Note 5)
0.3
OC
Change in Magnitude of
Common-Mode Output
Voltage (Normal to
Preemphasis)
∆V
Figure 1, R = 27Ω
50
mV
V
NP
2.4
DE, DI, RE
PEE
Input High Voltage
V
IH
3.75
Input Low Voltage
V
0.8
±2
V
DE, DI, RE, PEE
DE, DI, RE
IL
Input Current
I
IN
µA
µA
µA
PEE Input Current (MAX3291)
PSET Input Current (MAX3292)
I
-15
-30
70
-45
110
25
PEE
I
V
= V
PSET
PSET CC
V = V = +12V
Y
Z
DE = GND,
= GND or 5.25V
Output Leakage (Y and Z)
I
O
µA
V
CC
V = V = -7V
-25
Y
Z
Driver Short-Circuit Output
Current
I
-7V ≤ V
≤ +12V (Note 6)
±30
±250
mA
OSD
OUT
2
_______________________________________________________________________________________
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
1/MAX392
DC ELECTRICAL CHARACTERISTICS (continued)
(Typical Operating Circuit, V = +5V ±5%, R
= 0 (MAX3292), V = V
(MAX3292), T = T
A
to T , unless otherwise
MAX
CC
PSET
CC
CCD
MIN
noted. Typical values are at V = +5V and T = +25°C.) (Note 1)
CC
A
PARAMETER
RECEIVER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
= +12V
= -7V
250
IN
DE = GND,
Input Current (A and B)
I ,
A B
µA
V
= GND or 5.25V
CC
V
IN
-150
Receiver Differential
Threshold Voltage
V
-7V ≤ V ≤ +12V
-200
3.5
200
mV
TH
CM
Receiver Input Hysteresis
∆V
V
A
= V = 0
35
mV
V
TH
B
Receiver Output High Voltage
Receiver Output Low Voltage
V
OH
I = -4mA, V - V = V
O A B TH
V
OL
I
O
= 4mA, V - V = -V
TH
0.4
±1
V
A
B
Three-State Output Current at
Receiver
I
0 ≤ V ≤ V
CC
0.1
µA
kΩ
OZR
O
Receiver Input Resistance
R
-7V ≤ V ≤ +12V
48
IN
CM
Receiver Output Short-Circuit
Current
I
0 ≤ V ≤ V
CC
±15
±95
mA
OSR
RO
SUPPLY CURRENT
No-Load Supply Current
I
I
2.0
0.1
3.0
1
mA
µA
RE = GND, DE = V
CC + CCD
CC
Supply Current in Shutdown
Mode
RE = V
DE = GND, V = V = 0 to V or
Y Z CC
CC,
I
SHDN
floating
SWITCHING CHARACTERISTICS
(Typical Operating Circuit, V = +5V ±5%, R
= 0 (MAX3292), V = V
(MAX3292), T = +25°C, unless otherwise noted.
CCD A
CC
PSET
CC
Typical values are at V = +5V and T = +25°C.)
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
41
MAX
65
UNITS
t
t
DPLH
DPHL
Figures 3 and 5, R
= 54Ω,
DIFF
Driver Propagation Delay
ns
C
= C = 50pF
L2
L1
44
65
t
t
HL
LH
Driver Differential Output
Rise or Fall Time
Figures 3 and 5, R
= C = 50pF
= 54Ω,
DIFF
12
100
1
ns
ns
µs
ns
C
L1
L2
MAX3291/MAX3292,
= 0
80
120
Figures 3 and 10,
R
PSET
Driver Preemphasis Interval
t
R
C
= 54Ω,
DIFF
PRE
MAX3292,
= 523kΩ
= C = 50pF
L1
L2
0.75
1.25
R
PSET
Preemphasis Voltage Level to
Normal Voltage Level Delay
Figures 3 and 10, R
= 54Ω,
DIFF
t
30
3
PTND
C
= C = 50pF
L2
L1
Differential Driver Output
Figures 3 and 5, R
= 54Ω,
DIFF
t
8
ns
DSKEW
Skew
t
- t
C
= C = 50pF
L1 L2
DPLH DPHL
Maximum Data Rate
f
10
Mbps
MAX
_______________________________________________________________________________________
3
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
SWITCHING CHARACTERISTICS (continued)
(Typical Operating Circuit, V = +5V ±5%, R
= 0 (MAX3292), V = V
(MAX3292), T = +25°C, unless otherwise noted.
CCD A
CC
PSET
CC
Typical values are at V = +5V and T = +25°C.)
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Figures 2 and 6, S2 closed, R = 500Ω,
L
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable Time from Low
Driver Disable Time from High
t
72
105
ns
DZH
C
= 100pF
L
Figures 2 and 6, S1 closed, R = 500Ω,
L
t
55
53
71
105
100
100
ns
ns
ns
ns
ns
ns
ns
ns
DZL
DLZ
DHZ
C
= 100pF
L
Figures 2 and 6, S1 closed, R = 500Ω,
L
t
C
= 15pF
L
Figures 2 and 6, S2 closed, R = 500Ω,
L
t
C
= 15pF
L
t
t
49
52
85
85
RPLH
RPHL
Figures 7 and 9, C = 50pF, V = 2V,
L
ID
Receiver Propagation Delay
Receiver Output Skew
V
CM
= 0
1/MAX392
t
Figures 7 and 9, C = 100pF
3
RSKEW
L
t
- t
RPLH RPHL
Receiver Enable to Output
Low
Figures 2 and 8, R = 1kΩ, C = 100pF,
L
L
t
3
3
43
43
25
55
55
45
RZL
S1 closed
Receiver Enable to Output
High
Figures 2 and 8, R = 1kΩ, C = 100pF,
L
L
t
RZH
S2 closed
Receiver Disable Time from
Low
Figures 2 and 8, R = 1kΩ, C = 15pF,
L
L
t
RLZ
S1 closed
Receiver Disable Time from
High
Figures 2 and 8, R = 1kΩ, C = 15pF,
L
L
t
25
45
ns
ns
ns
RHZ
S2 closed
Figures 4 and 11 (Note 7)
Figures 2 and 6, R = 500Ω, C = 100pF,
Time to Shutdown
t
50
160
500
SHDN
Driver Enable from Shutdown
to Output High
L
L
t
t
6000
8750
DZH(SHDN)
S2 closed
Driver Enable from Shutdown
to Output Low
Figures 2 and 6, R = 500Ω, C = 100pF,
L
L
t
6000
850
30
8750
1500
1500
ns
ns
ns
DZL(SHDN)
S1 closed
Receiver Enable from
Shutdown to Output High
Figures 2 and 8, R = 1kΩ, C = 100pF,
L
L
RZH(SHDN)
S2 closed
Receiver Enable from
Shutdown to Output Low
Figures 2 and 8, R = 1kΩ, C = 100pF,
L
L
t
RZL(SHDN)
S1 closed
Note 1: All currents into the device are positive; all currents out of the device are negative. All voltages are referenced to device
ground unless otherwise noted.
Note 2: Guaranteed by design.
Note 3: DPER is defined as (V
/ V ).
OD
ODP
Note 4: ∆V
and ∆V are the changes in V and V , respectively, when the DI input changes. This specification reflects
DD OC
OC
ODP
constant operating conditions. When operating conditions shift, the maximum value may be momentarily exceeded.
Note 5: ∆V and ∆V are the changes in V and V , respectively, when the DI input changes state.
ODP
OC
OD
OC
Note 6: Maximum current level applies to peak current just prior to foldback-current limiting; minimum current level applies during
current limiting.
Note 7: Shutdown is enabled by bringing RE high and DE low. If the enable inputs are in this state for less than 50ns, the device is
guaranteed not to enter shutdown. If the enable inputs are in this state for at least 500ns, the device is guaranteed to have
entered shutdown. Time to shutdown for the device (t ) is measured by monitoring R0 as in Figure 4.
SHDN
4
_______________________________________________________________________________________
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
1/MAX392
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(V = +5V, T = +25°C, unless otherwise noted.)
CC
A
PREEMPHASIS INTERVAL vs. R
PSET
(C
PSET
= 0.1µF)
TYPICAL PREEMPHASIS WAVEFORM
R
PRE
AND t
vs. t
PRE BAUD
2500
2250
2000
1750
1500
1250
1000
1200
1000
800
600
400
200
0
V - V
2V/
div
Y
Z
NOTE A
NOTE A
750
500
250
0
800
100ns/div
0
100 200 300 400 500 600 700
(kΩ)
900 1000
0
500
1000
(ns)
1500
2000
R
t
PSET
BAUD
RECEIVER PROPAGATION DELAY
vs. TEMPERATURE
DRIVER DIFFERENTIAL
DRIVER DIFFERENTIAL
OUTPUT VOLTAGE vs. TEMPERATURE
OUTPUT VOLTAGE vs. R
DIFF
60.0
57.5
55.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
4.25
C = 50pF
L
STRONG
STRONG (V
)
ODP
4.00
3.75
3.50
3.25
3.00
2.75
2.50
2.25
2.00
NORMAL
52.5
50.0
47.5
45.0
42.5
40.0
NORMAL (V
)
OD
R
DIFF
= 54Ω
100
100
100
-40 -20
0
20
40
60
80
10 20 30 40 50 60 70 80 90
(Ω)
-40 -20
0
20
40
60
80
TEMPERATURE (°C)
R
DIFF
TEMPERATURE (°C)
DRIVER PROPAGATION DELAY
vs. TEMPERATURE
RECEIVER PROPAGATION DELAY
50.0
47.5
45.0
C
L1
= C = 50pF
L2
42.5
40.0
37.5
35.0
32.5
30.0
2.5V/
div
V - V
A
B
5V/
div
RO
100
-40 -20
0
20
40
60
80
20ns/div
TEMPERATURE (°C)
Note A: Dotted line represents region in which preemphasis may not work in systems with excessive power-supply noise. See
Preemphasis at Low Data Rates.
_______________________________________________________________________________________
5
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
____________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(V = +5V, T = +25°C, unless otherwise noted.)
CC
A
RECEIVER OUTPUT LOW VOLTAGE
vs. TEMPERATURE
RECEIVER OUTPUT HIGH VOLTAGE
vs. TEMPERATURE
DRIVER PROPAGATION DELAY
0.30
0.25
4.60
4.55
4.50
4.45
4.40
4.35
4.30
4.25
4.20
4.15
4.10
I
RO
= 8mA
I = 8mA
RO
5V/
div
DI
0.20
0.15
2.5V/
div
V - V
Y
Z
0.10
0.05
0
100
100
-40 -20
0
20
40
60
80
-40 -20
0
20
40
60
80
20ns/div
1/MAX392
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT SINK CURRENT vs.
RECEIVER OUTPUT LOW VOLTAGE
OUTPUT SOURCE CURRENT vs.
RECEIVER OUTPUT HIGH VOLTAGE
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
70
60
50
40
30
20
10
0
30
25
20
15
10
5
3.00
2.75
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
0
100
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
OUTPUT LOW VOLTAGE (V)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
OUTPUT HIGH VOLTAGE (V)
-40 -20
0
20
40
60
80
TEMPERATURE (°C)
6
_______________________________________________________________________________________
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
1/MAX392
P in De s c rip t io n
PIN
NAME
PEE
FUNCTION
MAX3291
MAX3292
Preemphasis Enable Input. To enable preemphasis, leave PEE unconnected, connect to
1
—
V
CC
, or drive high. To enable strong-level-drive only mode, connect PEE to GND or drive
low.
Preemphasis Set Input. Sets the preemphasis interval. Connect a resistor (R
) in paral-
PSET
—
1
PSET
lel with a capacitor (C
Operating Circuit.
) from PSET to V to set the preemphasis interval. See Typical
PSET CC
Receiver Output. When RE is low and if A - B ≥ 200mV, RO is high; if A - B ≤ -200mV, RO
is low.
2
3
4
2
3
4
RO
RE
DE
Receiver Output Enable. Drive RE low to enable RO; RO is high impedance when RE is
high. Drive RE high and DE low to enter low-power shutdown mode.
Driver Output Enable. Drive DE high to enable the driver outputs. These outputs are high
impedance when DE is low. Drive RE high and DE low to enter low-power shutdown mode.
Driver Input. With DE high, a low on DI forces the noninverting output low and the inverting
output high. Similarly, a high on DI forces the noninverting output high and the inverting
output low.
5
5
DI
6, 8, 13
8
6, 7
9
N.C.
GND
Y
No Connection. Not internally connected.
Ground
7
9
Noninverting Driver Output
Inverting Driver Output
Inverting Receiver Input
Noninverting Receiver Input
10
11
12
—
14
10
11
12
13
14
Z
B
A
V
CCD
Connect to V
CC
V
CC
Positive Supply: +4.75V ≤ V ≤ +5.25V
CC
Y
R
V
CC
S1
S2
R
L
V
V
ODP
OD
OUTPUT
UNDER TEST
C
L
R
V
OC
Z
Figure 2. Driver or Receiver Enable/Disable Timing Test Load
_______________________________________________________________________________________
Figure 1. Driver DC Test Load
7
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
5V
t < t
SHDN
t > t
SHDN
DE
C
L1
RE
Y
Z
DI
R
D
DIFF
V
ODP
t
RZH(SHDN)
C
L2
RO
DE = LOW
Figure 3. Driver Timing Test Circuit
Figure 4. Shutdown Timing Diagram
1/MAX392
5V
5V
DI
1.5V
1.5V
DE
1.5V
1.5V
0
t
t
DPHL
DPLH
0
Z
P
Y
P
V
PH
Z
N
Y
N
t
DLZ
t
, t
DZL(SHDN) DZL
Y, Z
0 DIFFERENTIAL
OUTPUT NORMALLY LOW
2.3V
V * + 0.5V
OL
Z
N
Y
N
Z
P
Y
P
OUTPUT NORMALLY HIGH
V
DIFF
= V - V
Y Z
Y, Z
0
V
DIFF
0 DIFFERENTIAL
20%
V * - 0.5V
OH
2.3V
80%
80%
20%
V
PL
t
, t
t
DHZ
DZH(SHDN) DZH
t
LH
t
HL
t
t
- t
SKEW = | PLH PHL |
Y - Z = V
|
|
N
N |
OD
*NOTE: V AND V ARE THE OUTPUT LEVELS IN FIGURE 2 WITH
OH
OL
Y - Z = V
P |
P
ODP
S2 AND S1 CLOSED, RESPECTIVELY.
Figure 5. Driver Propagation Delays
Figure 6. Driver Enable and Disable Times
3V
1.5V
1.5V
RE
V
OH
0
RO
1.5V
t
1.5V
V
OL
t
t
, t
RLZ
RZL(SHDN) RZL
t
RPLH
RPHL
V
RO
CC
1.5V
V
+ 0.5V
- 0.5V
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
OL
A
B
+1V
-1V
0 DIFFERENTIAL
RO
V
OH
1.5V
0
t
t
- t
RSKEW = | RPLH RPHL |
t
, t
t
RHZ
RZH(SHDN) RZH
Figure 7. Receiver Propagation Delays
Figure 8. Receiver Enable and Disable Times
8
_______________________________________________________________________________________
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
1/MAX392
t
PTND
Y
P
Z
P
80%
20%
Z
N
Y
N
B
A
RO
V
ID
R
ATE
0 DIFFERENTIAL
Z
N
C
L
Y
N
50%
Y
P
Z
P
t
PRE
Figure 9. Receiver Propagation Delay Test Circuit
Figure 10. Preemphasis Timing
V
CC
RE
1k
MAX3291
MAX3292
RO
DI
DE
Figure 11. Time-to-Shutdown Test Circuit
Fu n c t io n Ta b le s
RECEIVING
TRANSMITTING
INPUTS
OUTPUT
INPUTS
OUTPUTS
DE
X
A-B
≥ 0.2V
≤ -0.2V
Open
X
RO
RE
0
DE
1
DI
1
Z
0
1
Y
RE
X
1
1
0
0
X
0
1
X
1
0
0
X
0
0
X
High-Z
High-Z
1
1
High-Z
High-Z and
SHUTDOWN
High-Z and
SHUTDOWN
1
0
X
1
0
X
X = Don’t care
Z = High impedance
SHUTDOWN = Low-power shutdown; driver and receiver outputs are high impedance.
_______________________________________________________________________________________
9
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
De t a ile d De s c rip t io n
The MAX3291/MAX3292 high-speed RS-485/RS-422
SIGNAL 1
transceivers feature driver preemphasis circuitry, which
extends the distance and increases the data rate of
reliable communication by reducing intersymbol inter-
BAUD PERIOD
ference (ISI) caused by long cables. The MAX3291 is
programmable for data rates of 5Mbps to 10Mbps,
V - V
A
B
while the MAX3292 is programmable for data rates up
to 10Mbps by using a single external resistor.
The MAX3291/MAX3292 are full-duplex devices that
operate from a single +5V supply and offer a low-cur-
rent shutdown mode that reduces supply current to
100nA. They feature driver output short-circuit current
limiting and a fail-safe receiver input that guarantees a
logic-high output if the input is open circuit. A 1/4-unit-
load receiver input impedance allows up to 128 trans-
ceivers on the bus.
t
ISI
SIGNAL 2
Figure 12. Inter-Symbol Interference among Two Data
Patterns: Signal 1 = 11111110, Signal 2 = 00000010
Inter-symbol interference (ISI) causes significant prob-
lems for UARTs if the total RS-485/RS-422 signal jitter
b e c ome s 10% or more of the b a ud p e riod . ISI is
caused by the effect of the cable’s RC time constant on
different bit patterns. If a series of ones is transmitted,
followed by a zero, the transmission-line voltage rises
to a high value at the end of the string of ones (signal 1
in Figure 12). As the signal moves towards the zero
s ta te , it ta ke s long e r to re a c h the ze ro-c ros s ing ,
because its starting voltage is farther from the zero
crossing. On the other hand, if the data pattern has a
string of zeros followed by a one and then another zero,
the one-to-zero transition starts from a voltage that is
1/MAX392
V - V
Y
Z
2.5V/div
5V/div
DI
much closer to the zero-crossing (V - V = 0) and it
A
B
takes much less time for the signal to reach the zero-
crossing (signal 2 in Figure 12). In other words, the
propagation delay depends upon the previous bit pat-
tern. This is inter-symbol interference (ISI).
0
1
1
1
0
0
0
1
0
1
100ns
Pre e mp ha s is re d uc e s ISI b y inc re a s ing the s ig na l
amplitude at every transition edge for about one baud
period, counteracting the effects of the cable (see the
section Setting the Preemphasis Interval). Figure 13
shows a typical preemphasis waveform optimized for
d a ta ra te s b e twe e n 5Mb p s a nd 10Mb p s . Whe n DI
changes from a logic low to a logic high, the differential
output switches to a strong high. At the end of the pre-
emphasis interval, the strong high returns to a normal
high level. Both levels meet RS-485/RS-422 specifica-
tions, and the strong levels are typically 1.9 times larger
than the normal levels. If DI switches back to a logic
low before the end of the preemphasis interval, the dif-
ferential output switches directly from the strong high to
the strong low. Similarly, this explanation applies when
DI transitions from high to low.
Figure 13. Typical Preemphasis Waveform with a 100ns
Preemphasis Interval
Ap p lic a t io n s In fo rm a t io n
Da t a Ra t e vs . Ca b le Le n g t h
In general, preemphasis allows either double the dis-
tance for a fixed data rate or double the data rate for a
fixe d e xis ting c a b le d is ta nc e ove r e xis ting RS-485
transceivers that do not feature preemphasis. Figure 14
shows that the MAX3291/MAX3292 transmits approxi-
mately twice as far at the same data rate or twice as
fast at the same cable length as a conventional RS-485
transceiver without preemphasis for 10% jitter.
10 ______________________________________________________________________________________
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
1/MAX392
S e t t in g t h e P re e m p h a s is In t e rva l
The MAX3291 has an internal fixed preemphasis interval
of 100ns. Use the MAX3291 for existing designs requiring
industry-standard ’75180 pin-compatibility at data rates of
5Mbps to 10Mbps.
Eye Dia g ra m s
One simple method to quickly determine your circuit
configuration is to view an eye diagram. An eye dia-
gram is a scope photo (voltage vs. time) showing the
transitions of a pseudo-random bit string displaying at
least one bit interval. Use an eye diagram to quickly
calculate the total jitter of a circuit configuration. Jitter is
the total time variation at the zero-volt differential cross-
ing, and percent jitter is expressed as a percentage of
The MAX3292 has a resistor-programmable preemphasis
interval for more flexibility. For data rates less than 1Mbps,
use the following equation to calculate R
emphasis setting resistor):
(the pre-
PSET
one baud period, t . Figures 15 and 16 show typi-
BAUD
R
PSET
= 580 (t
- 100)
BAUD
cal eye diagrams for a non-preemphasis device and
the MAX3291/MAX3292. ISI and jitter are often used
interchangeably; however, they are not exactly the
same thing. ISI usually makes up the majority of the jit-
ter, but asymmetrical high and low driver output voltage
levels and time skews of non-ideal transceivers (driver
and receiver) also contribute to jitter.
where t
= one baud period in ns.
BAUD
For example, a baud rate of 500kbps produces a baud
period of 2µs (2µs = 2000ns).
R
R
= 580 (t
= 580 (2000 - 100) = 1.1MΩ
- 100)
PSET
PSET
BAUD
For data rates of 1Mbps to 10Mbps, use the following
equation to calculate R
:
PSET
R
= 580 (t
- 100)(t
/ 1000)
PSET
BAUD
BAUD
where t
= one baud period in ns.
BAUD
For example, a baud rate of 1Mbps produces a baud
period of 1µs (1µs = 1000ns).
R
= 580 (1000 - 100)(1000 / 1000) = 522kΩ
PSET
(closest standard value is 523kΩ)
Set the preemphasis interval by connecting the R
PSET
resistor from PSET to V . Use a 0.1µF bypass capaci-
CC
tor (C
) from PSET to V . If PSET is connected
PSET
CC
directly to V
(R
= 0), the preemphasis interval
PSET
CC
reverts to the nominal 100ns value.
Figure 15. Eye Diagram of a Typical RS-485 Transceiver
Without Preemphasis, while Driving 1000 feet of Cable at
5Mbps
10,000
24-GAUGE
TWISTED PAIR
10% JITTER
PREEMPHASIS
485 DRIVER
LIMIT
1000
CONVENTIONAL
485 DRIVER
LIMIT
PREEMPHASIS REQUIRED
FOR ERROR-FREE
TRANSMISSION
100
0.1
1
10
DATA RATE (Mbps)
Figure 14. Preemphasis Driver Performance Compared to a
Conventional Driver Without Preemphasis at 10% Jitter
Figure 16. Eye Diagram of the MAX3292 with a Preemphasis
Interval of 175ns, while Driving 1000 feet of Cable at 5Mbps
______________________________________________________________________________________ 11
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
Lin e Re p e a t e r
For line le ng ths g re a te r tha n wha t one MAX3291/
MAX3292 c a n d rive , us e the re p e a te r a p p lic a tion
shown in Figure 17.
% Jitter = (total jitter / t
) · 100
BAUD
When the total amount of time skew becomes 10% or
more of the b a ud p e riod , the d a ta e rror ra te c a n
increase sharply.
Figure 18 shows the system differential voltage for the
MAX3292 driving 4000 feet of 26AWG twisted-pair wire
into two 120Ω termination loads.
1 2 8 Tra n s c e ive rs o n t h e Bu s
The standard RS-485 receiver input impedance is 12kΩ
(one unit load), and the standard driver can drive up to
32 unit loads. The MAX3291/MAX3292 transceivers have
a 1/4-unit-load receiver input impedance (48kΩ), allow-
ing up to 128 transceivers to be connected in parallel on
one c ommunic a tion line . Any c omb ina tion of the s e
devices and/or other RS-485 transceivers with a total of
32 unit-loads or less can be connected to the line.
Lin e Te rm in a t io n
The MAX3291/MAX3292 are targeted for applications
requiring the best combination of long cable length and
lowest bit-error rate. In order to achieve this combina-
tion, the cable system must be set up with care. There
are three basic steps:
1) The cable should only have two ends (no tree configu-
ration with long branches), which are terminated with
a s imp le re s is tor te rmina tion whos e va lue is the
Lo w -P o w e r S h u t d o w n Mo d e
Initiate low-power shutdown mode by bringing RE high
and DE low. In shutdown the MAX3291/MAX3292 typi-
cally draw only 1µA of supply current.
cable’s characteristic impedance (Z ). Avoid termina-
O
1/MAX392
tions anywhere else along the cable. This ensures that
there are no reflections at the end of the cable, and
that all transmitters (whether they are located at the
ends of the cable or somewhere along the length) see
Simultaneously driving RE and DE is allowed; the parts
are guaranteed not to enter shutdown if RE is high and
DE is low for less than 80ns. If the inputs are in this
state for at least 300ns, the parts are guaranteed to
enter shutdown.
the same impedance, equal to Z / 2.
O
2) Make all branches or stubs short enough so that
twice the propagation delay along the stub (down
and back) is significantly less than one baud period
(around 15% or less). This ensures that the reflec-
tions from the end of the stub (which are unavoid-
able, since the stubs are not terminated) settle in
much less than a baud period. If the application
re q uire s a b ra nc h muc h long e r tha n this , us e a
repeater (see the Line Repeater section).
Enable times t
tics tables correspond to when the part is not in the low-
power shutdown state. Enable times t and
and t in the Switching Characteris-
ZL
ZH
ZH(SHDN)
t
assume the parts are shut down. It takes dri-
ZL(SHDN)
vers and receivers longer to activate from the low-
power shutdown mode (t , t ) than from
the driver/receiver disable mode (t , t ).
ZH(SHDN) ZL(SHDN)
ZH ZL
MAX3291
MAX3292
5V/div
1V/div
DI
RECEIVER
INPUT
A
B
RO
RE
120Ω
120Ω
R
DATA IN
V - V
A
B
DE
DI
RO
5V/div
Z
DATA OUT
D
Y
2µs/div
TYPICAL OPERATING CIRCUIT, R
= 1MΩ
PSET
Figure 18. MAX3292 System Differential Voltage Driving 4000
Figure 17. Line-Repeater Application
Feet, Using Two 120Ω Termination Resistors
12 ______________________________________________________________________________________
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
1/MAX392
3) Don’t overload the cable with too many receivers.
Even though the MAX3291/MAX3292 receives pre-
sent only 1/4-unit load, placing 128 receivers on the
cable will attenuate the signal if spaced out along
the c a b le a nd , in a d d ition, c a us e re fle c tions if
clumped in one spot. The MAX3291/MAX3292 suc-
cessfully drive the cables to correct RS-485/RS-422
le ve ls with 128 re c e ive rs , b ut the p re e mp ha s is
effect is significantly diminished.
significantly less preemphasis. Determine the preempha-
sis ratio versus load by referring to the Driver Differential
Output Voltage vs. R
graph in the Typical Operating
DIFF
Characteristics. Read the strong and normal levels from
the graph (remember that the horizontal units are half
your cable impedance) and divide the two numbers to
get DPER (DPER = V
/ V
= V
/ V ).
STRONG
NORMAL
ODP OD
Figures 19 and 20 show typical network application cir-
cuits with proper termination.
The MAX3291/ MAX3292 are centered for a load imped-
ance of 54Ω, which corresponds to the parallel combina-
tion of the cable impedance and termination resistors. If
your cable impedance deviates somewhat from this
value, you still get the preemphasis effect (although the
P re e m p h a s is a t Lo w Da t a Ra t e s
(MAX3 2 9 2 )
At low data rates (<1Msps), preemphasis operation is
not guaranteed because it is highly dependent on the
system power-supply noise. Minimize this noise by
increasing bypass capacitance and using a power
supply with a fast transient response.
ideal preemphasis time, t
, may need adjustment).
PRE
However, if your cable impedance is significantly differ-
ent, the preemphasis ratio DPER changes, resulting in
DE
Z
Z
DI
D
R = Z
R = Z
O
O
D
DI
Y
Y
B
DE
B
A
Z
Y
B
A
RO
RE
RO
RE
R
R
A
R
D
MAX3291
MAX3292
DI
DE
RO RE
Figure 19. Typical Half-Duplex RS-485 Network
A
Y
R = Z
O
R = Z
O
RO
RE
R
DI
D
B
Z
Z
B
DE
DE
RE
RO
R = Z
R = Z
O
O
DI
R
D
Y
A
Y
Z
B
A
Y
Z
B
A
R
R
MAX3291
MAX3292
D
DI
D
DI
DE RE RO
DE RE RO
NOTE: RE AND DE ON.
Figure 20. Typical Full-Duplex RS-485 Network
______________________________________________________________________________________ 13
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
P in Co n fig u ra t io n
Ch ip In fo rm a t io n
TRANSISTOR COUNT: 2280
SUBSTRATE CONNECTED TO GND
TOP VIEW
MAX3291
MAX3292
PEE (PSET)
RO
1
2
3
4
5
6
7
14
V
CC
13 N.C. (PV
)
CC
RE
12
11
10
9
A
DE
B
DI
Z
N.C. (GND)
GND
Y
8
N.C.
1/MAX392
SO/DIP
( ) ARE FOR THE MAX3292 ONLY.
14 ______________________________________________________________________________________
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
1/MAX392
________________________________________________________P a c k a g e In fo rm a t io n
______________________________________________________________________________________ 15
RS-485/RS-422 Tra ns c e ive rs w ith Pre e m pha s is
for High-Spe e d, Long-Dis ta nc e Com m unic a tion
___________________________________________P a c k a g e In fo rm a t io n (c o n t in u e d )
1/MAX392
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Ma x im In t e g ra t e d P ro d u c t s , 1 2 0 S a n Ga b rie l Drive , S u n n yva le , CA 9 4 0 8 6 4 0 8 -7 3 7 -7 6 0 0
© 1999 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX3291 相关器件
型号 | 制造商 | 描述 | 价格 | 文档 |
MAX3291-MAX3292 | MAXIM | RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication | 获取价格 | |
MAX3291CPD | MAXIM | RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication | 获取价格 | |
MAX3291CSD | MAXIM | RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication | 获取价格 | |
MAX3291CSD-T | MAXIM | Line Transceiver, 1 Func, 1 Driver, 1 Rcvr, PDSO14, 0.150 INCH, MS-012B, SOIC-14 | 获取价格 | |
MAX3291EPD | MAXIM | RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication | 获取价格 | |
MAX3291ESD | MAXIM | RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication | 获取价格 | |
MAX3291ESD+T | MAXIM | 暂无描述 | 获取价格 | |
MAX3291ESD-T | MAXIM | Line Transceiver, 1 Func, 1 Driver, 1 Rcvr, PDSO14, 0.150 INCH, MS-012B, SOIC-14 | 获取价格 | |
MAX3292 | MAXIM | RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication | 获取价格 | |
MAX3292 | ADI | RS-485/RS-422收发器,带有预加重,用于高速、远距离通信 | 获取价格 |
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