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MAX481、MAX483、MAX485、MAX487-MAX491以及MAX1487规格
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_______________________________ 概述
MAX481、MAX483、MAX485、MAX487,MAX488,MAX489,MAX490,MAX491以及
MAX1487是用于RS-485与RS-422通信的低功耗收发器,
每个器件中都具有一个驱动器和一个接收器。MAX483、
MAX487、MAX488以及MAX489具有限摆率驱动器,可
以减小EMI,并降低由不恰当的终端匹配电缆引起的反射,
实现最高 250kbps 的无差错数据传输。 MAX481 、
MAX485、MAX490、MAX491、MAX1487 的驱动器摆
率不受限制,可以实现最高2.5Mbps的传输速率。
这些收发器在驱动器禁用的空载或满载状态下,吸取的
电源电流在 120(A 至500(A 之间。另外, MAX481 、
MAX483 与MAX487 具有低电流关断模式,仅消耗
0.1?A。所有器件都工作在5V单电源下。
驱动器具有短路电流限制,并可以通过热关断电路将驱
动器输出置为高阻状态,防止过度的功率损耗。接收器
输入具有失效保护特性,当输入开路时,可以确保逻辑
高电平输出。
MAX487与MAX1487具有四分之一单位负载的接收器输
入阻抗,使得总线上最多可以有 128 个MAX487/
MAX1487收发器。使用MAX488-MAX491可以实现全双
工通信,而MAX481、MAX483、MAX485、MAX487与
MAX1487则为半双工应用设计。
_______________________________ 应用
低功耗RS-485收发器
低功耗RS-422收发器
电平转换器
用于EMI敏感应用的收发器
工业控制局域网
____________________ 下一代器件的特性
〓容错应用
MAX3430: ±80V故障保护、失效保护、1/4单位
负载、+3.3V、RS-485收发器
MAX3440E-MAX3444E: ±15kV ESD保护、±60V
故障保护、10Mbps、失效保护、
RS-485/J1708收发器
〓对于空间受限应用
MAX3460-MAX3464: +5V、失效保护、20Mbps、
Profibus RS-485/RS-422收发器
MAX3362: +3.3V、高速、RS-485/RS-422收发器,
采用SOT23封装
MAX3280E-MAX3284E: ±15kV ESD保护、
52Mbps、+3V至+5.5V、SOT23、
RS-485/RS-422、真失效保护接收器
MAX3293/MAX3294/MAX3295: 20Mbps、+3.3V、
SOT23、RS-485/RS-422发送器
〓对于多通道收发器应用
MAX3030E-MAX3033E: ±15kV ESD保护、
+3.3V、四路RS-422发送器
〓对于失效保护应用
MAX3080-MAX3089: 失效保护、高速(10Mbps)、
限摆率RS-485/RS-422收发器
〓对于低电压应用
MAX3483E/MAX3485E/MAX3486E/MAX3488E/
MAX3490E/MAX3491E: +3.3V供电、±15kV ESD
保护、12Mbps、限摆率、真正的RS-485/RS-422
收发器
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
________________________________________________________________ Maxim Integrated Products 1
_____________________________________________________________________ 选择表
19-0122; Rev 8; 10/03
MAX481
MAX483
MAX485
MAX487
MAX488
MAX489
MAX490
MAX491
MAX1487
PART
NUMBER
HALF/FULL
DUPLEX
DATA RATE
(Mbps)
SLEW-RATE
LIMITED
LOW-POWER
SHUTDOWN
RECEIVER/
DRIVER
ENABLE
QUIESCENT
CURRENT
(?A)
NUMBER OF
TRANSMITTERS
ON BUS
PIN
COUNT
Half
Half
Half
Half
Full
Full
Full
Full
Half
2.5
0.252.5
0.25
0.25
0.252.52.52.5
NoYesNoYesYesYesNoNoNo
YesYesNoYesNoNoNoNoNo
YesYesYesYesNoYesNoYesYes
300120300120120120300300230
32323212832323232128
88888148148
定购信息在本资料的最后给出。
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC).............................................................12V
Control Input Voltage (RE, DE)...................-0.5V to (VCC + 0.5V)
Driver Input Voltage (DI).............................-0.5V to (VCC + 0.5V)
Driver Output Voltage (A, B)...................................-8V to +12.5V
Receiver Input Voltage (A, B).................................-8V to +12.5V
Receiver Output Voltage (RO).....................-0.5V to (VCC +0.5V)
Continuous Power Dissipation (TA = +70°C)
8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ....727mW
14-Pin Plastic DIP (derate 10.00mW/°C above +70°C)..800mW
8-Pin SO (derate 5.88mW/°C above +70°C).................471mW
14-Pin SO (derate 8.33mW/°C above +70°C)...............667mW
8-Pin ?MAX (derate 4.1mW/°C above +70°C)..............830mW
8-Pin CERDIP (derate 8.00mW/°C above +70°C).........640mW
14-Pin CERDIP (derate 9.09mW/°C above +70°C).......727mW
Operating Temperature Ranges
MAX4_ _C_ _/MAX1487C_ A ...............................0°C to +70°C
MAX4_ _E_ _/MAX1487E_ A.............................-40°C to +85°C
MAX4_ _MJ_/MAX1487MJA ...........................-55°C to +125°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
DC ELECTRICAL CHARACTERISTICS(VCC = 5V ±5%, TA = TMIN to TMAX, unless otherwise noted.) (Notes 1, 2)
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 specificatio ns is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
V
VIN = -7V
VIN = 12V
VIN = -7V
VIN = 12V
Input Current
(A, B)
IIN2VTH
k〓48-7V ≤VCM ≤12V, MAX487/MAX1487
RINReceiver Input Resistance
-7V ≤VCM ≤12V, all devices except
MAX487/MAX1487
R = 27〓(RS-485), Figure 4
0.4V ≤VO ≤2.4V
R = 50〓(RS-422)
IO = 4mA, VID = -200mV
IO = -4mA, VID = 200mV
VCM = 0V
-7V ≤VCM ≤12V
DE, DI, RE
DE, DI, RE
MAX487/MAX1487,
DE = 0V, VCC = 0V or 5.25V
DE, DI, RE
R = 27〓or 50〓, Figure 4
R = 27〓or 50〓, Figure 4
R = 27〓or 50〓, Figure 4
DE = 0V;VCC = 0V or 5.25V,
all devices except
MAX487/MAX1487
CONDITIONS
k〓12
?A±1IOZR
Three-State (high impedance)
Output Current at Receiver
V
0.4VOLReceiver Output Low Voltage
3.5VOHReceiver Output High Voltage
mV70〓VTHReceiver Input Hysteresis
V-0.2 0.2
Receiver Differential Threshold
Voltage
-0.2
mA
0.25
mA
-0.81.0
1.5 5
VOD2
Differential Driver Output
(with load)
V
2
V5VOD1Differential Driver Output (no load)
?A±2IIN1Input Current
V0.8VILInput Low Voltage
V2.0VIHInput High Voltage
V0.2〓VOD
Change in Magnitude of Driver
Common-Mode Output Voltage
for Complementary Output States
V0.2〓VOD
Change in Magnitude of Driver
Differential Output Voltage for
Complementary Output States
V3VOC
Driver Common-Mode Output
Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
_______________________________________________________________________________________ 3
SWITCHING CHARACTERISTICS—MAX481/MAX485, MAX490/MAX491, MAX1487(VCC= 5V ±5%, TA = TMINto TMAX, unless otherwise noted.) (Notes 1, 2)
DC ELECTRICAL CHARACTERISTICS (continued)(VCC = 5V ±5%, TA = TMIN to TMAX, unless otherwise noted.) (Notes 1, 2)
mA79 50V ≤VO ≤VCCIOSRReceiver Short-Circuit Current
mA35 250-7V ≤VO ≤12V (Note 4)IOSD2
Driver Short-Circuit Current,VO = Low
mA35 250-7V ≤VO ≤12V (Note 4)IOSD1
Driver Short-Circuit Current,VO = High
MAX1487,RE = 0V or VCC
250 400
350 650
ns
10 30 60tPHL
Driver Rise or Fall Time
Figures 6 and 8, RDIFF= 54〓, CL1= CL2= 100pF
ns
MAX490M, MAX491M
MAX490C/E, MAX491C/E 20 90 150
MAX481, MAX485, MAX1487
MAX490M, MAX491M
MAX490C/E, MAX491C/E
MAX481, MAX485, MAX1487
Figures 6 and 8, RDIFF = 54〓,
CL1 = CL2 = 100pF
MAX481 (Note 5)
Figures 5 and 11, CRL = 15pF, S2 closed
Figures 5 and 11, CRL = 15pF, S1 closed
Figures 5 and 11, CRL = 15pF, S2 closed
Figures 5 and 11, CRL = 15pF, S1 closed
Figures 6 and 10, RDIFF = 54〓,
CL1 = CL2 = 100pF
Figures 6 and 8,RDIFF = 54〓,
CL1= CL2= 100pF
Figures 6 and 10,RDIFF = 54〓,
CL1= CL2= 100pF
CONDITIONS
ns
51 0tSKEW
ns50 200 600tSHDNTime to Shutdown
Mbps2.5fMAXMaximum Data Rate
ns20 50tHZReceiver Disable Time from High
ns
10 30 60tPLH
20 50tLZReceiver Disable Time from Low
ns20 50tZH
Driver Input to Output
Receiver Enable to Output High
ns20 50tZLReceiver Enable to Output Low
20 90 200
nsns
1340 70tHZ
tSKD
Driver Disable Time from High| tPLH - tPHL | Differential
Receiver Skew
ns40 70tLZDriver Disable Time from Low
ns
40 70tZLDriver Enable to Output Low
31 5 40
ns
51 5 25 ns
31 5 40
tR, tF
20 90 200
Driver Output Skew to Output
tPLH, tPHLReceiver Input to Output
40 70tZHDriver Enable to Output High
UNITSMIN TYP MAXSYMBOLPARAMETER
CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER
230 400
300 500
MAX481/MAX485,RE = 0V or VCC
500 900
MAX490/MAX491,
DE, DI, RE = 0V or VCC
300 500
MAX488/MAX489,
DE, DI, RE = 0V or VCC
120 250
DE = VCC
300 500DE = 0V
DE = VCC
DE = 0V
?AMAX481/483/487, DE = 0V, RE = VCC 0.1 10ISHDNSupply Current in Shutdown
120 250
ICC
No-Load Supply Current
(Note 3)
DE = 5V
DE = 0V
MAX483
MAX487
MAX483/MAX487,RE = 0V or VCC
Figures 7 and 9, CL = 100pF, S2 closed
Figures 7 and 9, CL = 100pF, S1 closed
Figures 7 and 9, CL = 15pF, S1 closed
Figures 7 and 9, CL = 15pF, S2 closed
?A
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
4 _______________________________________________________________________________________
SWITCHING CHARACTERISTICS—MAX483, MAX487/MAX488/MAX489(VCC = 5V ±5%, TA = TMIN to TMAX, unless otherwise noted.) (Notes 1, 2)
SWITCHING CHARACTERISTICS—MAX481/MAX485, MAX490/MAX491, MAX1487 (continued)(VCC= 5V ±5%, TA = TMINto TMAX, unless otherwise noted.) (Notes 1, 2)
300 1000
Figures 7 and 9, CL = 100pF, S2 closed
Figures 7 and 9, CL = 100pF, S1 closed
Figures 5 and 11, CL = 15pF, S2 closed,
A - B = 2V
CONDITIONS
ns40 100tZH(SHDN)
Driver Enable from Shutdown to
Output High (MAX481)
ns
Figures 5 and 11, CL = 15pF, S1 closed,
B - A = 2V
tZL(SHDN)
Receiver Enable from Shutdown
to Output Low (MAX481)
ns40 100tZL(SHDN)
Driver Enable from Shutdown to
Output Low (MAX481)
ns300 1000tZH(SHDN)
Receiver Enable from Shutdown
to Output High (MAX481)
UNITSMIN TYP MAXSYMBOLPARAMETER
tPLH
tSKEW
Figures 6 and 8, RDIFF = 54〓,
CL1 = CL2 = 100pF
tPHL
Figures 6 and 8, RDIFF = 54〓,
CL1 = CL2 = 100pF
Driver Input to Output
Driver Output Skew to Output ns100 800
nsns2000
MAX483/MAX487, Figures 7 and 9,CL = 100pF, S2 closed
tZH(SHDN)
Driver Enable from Shutdown to
Output High
250 2000
ns2500
MAX483/MAX487, Figures 5 and 11,
CL = 15pF, S1 closed
tZL(SHDN)
Receiver Enable from Shutdown
to Output Low
ns2500
MAX483/MAX487, Figures 5 and 11,
CL = 15pF, S2 closed
tZH(SHDN)
Receiver Enable from Shutdown
to Output High
ns2000
MAX483/MAX487, Figures 7 and 9,CL = 100pF, S1 closed
tZL(SHDN)
Driver Enable from Shutdown to
Output Low
ns50 200 600MAX483/MAX487 (Note 5) tSHDNTime to Shutdown
tPHL
tPLH, tPHL < 50% of data period
Figures 5 and 11, CRL = 15pF, S2 closed
Figures 5 and 11, CRL = 15pF, S1 closed
Figures 5 and 11, CRL = 15pF, S2 closed
Figures 5 and 11, CRL = 15pF, S1 closed
Figures 7 and 9, CL = 15pF, S2 closed
Figures 6 and 10, RDIFF = 54〓,
CL1 = CL2 = 100pF
Figures 7 and 9, CL = 15pF, S1 closed
Figures 7 and 9, CL = 100pF, S1 closed
Figures 7 and 9, CL = 100pF, S2 closed
CONDITIONS
kbps250fMAX
250 800 2000
Maximum Data Rate
ns20 50tHZReceiver Disable Time from High
ns
250 800 2000
20 50tLZReceiver Disable Time from Low
ns20 50tZHReceiver Enable to Output High
ns20 50tZLReceiver Enable to Output Low
nsns
100
300 3000tHZ
tSKD
Driver Disable Time from HighI tPLH - tPHL I Differential
Receiver Skew
Figures 6 and 10, RDIFF = 54〓,
CL1 = CL2 = 100pF
ns300 3000tLZDriver Disable Time from Low
ns250 2000tZLDriver Enable to Output Low
ns
Figures 6 and 8, RDIFF = 54〓,
CL1 = CL2 = 100pF
ns250 2000tR, tF
250 2000
Driver Rise or Fall Time
ns
tPLH
Receiver Input to Output
250 2000tZHDriver Enable to Output High
UNITSMIN TYP MAXSYMBOLPARAMETER
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
_______________________________________________________________________________________ 5
30
0
0 2.5
OUTPUT CURRENT vs.
RECEIVER OUTPUT LOW VOLTAGE
5
25
MAX481-01
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
1.5
1510
0.5 1.0 2.0
203540450.90.1
-50 -25 25 75
RECEIVER OUTPUT LOW VOLTAGE vs.
TEMPERATURE
0.30.7
TEMPERATURE (°C)
OUTPUT LOW VOLTAGE (V)
05 0
0.50.80.20.60.4
0
100 125
MAX481-04IRO = 8mA
-20
-4
1.5 2.0 3.0 5.0
OUTPUT CURRENT vs.
RECEIVER OUTPUT HIGH VOLTAGE
-8
-16
MAX481-02
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
2.5 4.0
-12-18
-6
-14-10
-20
3.5 4.5
4.83.2
-50 -25 25 75
RECEIVER OUTPUT HIGH VOLTAGE vs.
TEMPERATURE
3.64.4
TEMPERATURE (°C)
OUTPUT HIGH VOLTAGE (V)
05 0
4.04.63.44.23.83.0
100 125
MAX481-03IRO = 8mA
90
0
0 1.0 3.0 4.5
DRIVER OUTPUT CURRENT vs.
DIFFERENTIAL OUTPUT VOLTAGE
1070
MAX481-05
DIFFERENTIAL OUTPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
2.0 4.0
503080604020
0.5 1.5 2.5 3.5
2.31.5
-50 -25 25 125
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
vs. TEMPERATURE
1.72.1
MAX481-06
TEMPERATURE (°C)
DIFFERENTIAL OUTPUT VOLTAGE (V)
07 5
1.92.21.62.01.8
10050
2.4
R = 54〓
_______________________________________________________________ 典型工作特性
(VCC = 5V, TA = +25°C, unless otherwise noted.)
NOTES FOR ELECTRICAL/SWITCHING CHARACTERISTICS
Note 1: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to device
ground unless otherwise specified.
Note 2: All typical specifications are given for VCC = 5V and TA = +25°C.
Note 3: Supply current specification is valid for loaded transmitters when DE = 0V.
Note 4: Applies to peak current. See Typical Operating Characteristics.
Note 5: The MAX481/MAX483/MAX487 are put into shutdown by bringing RE high and DE low. If the inputs are in this state for less
than 50ns, the parts are guaranteed not to enter shutdown. If the inputs are in this state for at least 600ns, the parts are
guaranteed to have entered shutdown. See Low-Power Shutdown Mode section.
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
6 _______________________________________________________________________________________
__________________________________________________________ 典型工作特性(续)
(VCC = 5V, TA = +25°C, unless otherwise noted.)
120
0
08
OUTPUT CURRENT vs.
DRIVER OUTPUT LOW VOLTAGE
20
100
MAX481-07
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
6
6040
24
80
10 12
140 -120
0
-7 -5 -1 5
OUTPUT CURRENT vs.
DRIVER OUTPUT HIGH VOLTAGE
-20-80
MAX481-08
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
-3 1
-60
3-6 -4 -2 0 2 4
-100
-40
100
-40-60 -20 40 100 120
MAX1487
SUPPLY CURRENT vs. TEMPERATURE
300
MAX481-13
TEMPERATURE (°C)
SUPPLY CURRENT (?A)
20 60 80
500200600400
0
0 140
MAX1487; DE = VCC, RE = X
MAX1487; DE = 0V, RE = X
100
-50 -25 50 100
MAX481/MAX485/MAX490/MAX491
SUPPLY CURRENT vs. TEMPERATURE
300
MAX481-11
TEMPERATURE (°C)
SUPPLY CURRENT (?A)
25 75
500200600400
0
0 125
MAX481/MAX485; DE = VCC, RE = X
MAX485; DE = 0, RE = X,
MAX481; DE = RE = 0
MAX490/MAX491; DE = RE = X
MAX481; DE = 0, RE = VCC
100
-50 -25 50 100
MAX483/MAX487-MAX489
SUPPLY CURRENT vs. TEMPERATURE
300
MAX481-12
TEMPERATURE (°C)
SUPPLY CURRENT (?A)
25 75
500200600400
0
0 125
MAX483; DE = VCC, RE = X
MAX487; DE = VCC, RE = X
MAX483/MAX487; DE = 0, RE = VCC
MAX483/MAX487; DE = RE = 0,
MAX488/MAX489; DE = RE = X
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
_______________________________________________________________________________________ 7
___________________________________________________________________ 引脚说明
MAX481
MAX483
MAX485
MAX487
MAX1487
TOP VIEW
NOTE: PIN LABELS Y AND Z ON TIMING, TEST, AND WAVEFORM DIAGRAMS REFER TO PINS A AND B WHEN DE IS HIGH.
TYPICAL OPERATING CIRCUIT SHOWN WITH DIP/SO PACKAGE.
1234
85
VCC
GND DIDERERO RD
RtRt
76
D
R
DERE
DIROAB
1234
8765
VCC
BA
GND DIDERERO
DIP/SORD
1234
8765
VCC
A
GND DERE
B
RO
?MAX
BA
DI
MAX481
MAX483
MAX485
MAX487
MAX1487
图1. MAX481/MAX483/MAX485/MAX487/MAX1487引脚配置与典型工作电路
?MAX
——5678—2—13—
?MAX
4567——8—1—2—
DIP/SO DIP/SO
2 3
Receiver Output Enable. RO is enabled when RE is low; RO is
high impedance when RE is high.
3 4
Driver Output Enable. The driver outputs, Y and Z, are enabled
by bringing DE high. They are high impedance when DE is low. If
the driver outputs are enabled, the parts function as line drivers.
While they are high impedance, theyfunction as line receivers if
RE is low.
DIP/SO
—
4 5
Driver Input. A low on DI forces output Y low and output Z high.
Similarly, a high on DI forces output Y high and output Z low.
5 6, 7 Ground
— 9 Noninverting Driver Output
— 10 Inverting Driver Output
—34
6 — Noninverting Receiver Input and Noninverting Driver Output
— 12 Noninverting Receiver Input
56—8
REDEDI
GND
YZAA
7 — — B Inverting Receiver Input and Inverting Driver Output
— 7 11 B Inverting Receiver Input
8 1 14 VCC Positive Supply: 4.75V ≤VCC ≤5.25V
— — 1, 8, 13 N.C. No Connect—not internally connected
FUNCTIONNAME
431 2
Receiver Output: If A > B by 200mV, RO will be high;
If A < B by 200mV, RO will be low.
2 RO
PIN
FUNCTIONNAME
MAX481/MAX483/
MAX485/MAX487/
MAX1487
MAX488/
MAX490
MAX489/
MAX491
引脚
名称 功能
接收器输出:若A > B 200mV,则RO为高电平;
若A < B 200mV,则RO为低电平。
接收器输出使能。当RE为低电平时,RO有效;
当RE为高电平时,RO为高阻状态。
驱动器输出使能。DE变为高电平时,驱动器输出Y与Z有效;
当DE为低电平时,驱动器输出为高阻状态。
当驱动器输出有效时,器件被用作线驱动器。而高阻状态下,若RE为低电平,则器件被用作线接收器。
驱动器输入。DI上的低电平强制输出Y为低电平,而输出Z为高电平。
同理,DI上的高电平强制输出Y为高电平,而输出Z为低电平。
地
驱动器同相输出端
驱动器反相输出端
接收器同相输入端和驱动器同相输出端
接收器同相输入端
接收器反相输入端和驱动器反相输出端
接收器反相输入端
正电源:4.75V ≤VCC ≤5.25V
未连接——内部未连接
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
____________________________ 应用说明
MAX481/MAX483/MAX485/MAX487-MAX491 以及
MAX1487是用于RS-485与RS-422通信的低功耗收发器。
MAX481、MAX485、MAX490、MAX491以及MAX1487
能够以最高 2.5Mbps 的数据速率发送并接收数据;而
MAX483、MAX487、MAX488以及MAX489则用于最高
250kbps 的数据速率。MAX488-MAX491 是全双工收发
器,MAX481 、MAX483 、MAX485 、MAX487 以及
MAX1487是半双工收发器。另外,MAX481、MAX483、
MAX485、MAX487、MAX489、MAX491以及MAX1487
中包含驱动器使能 (DE) 与接收器使能 (RE)控制引脚,
被禁用时,驱动器或接收器输出为高阻态。
MAX487/MAX1487:
总线上可以接128个收发器
与
标准
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RS-485 驱动器( 最多32 个收发器 ) 的单位负载
(12k〓输入阻抗)相比,MAX487与MAX1487 具有48k〓
输入电阻,1/4单位负载的接收器输入阻抗,在一条总线
上允许最多挂接128个收发器。MAX487/MAX1487与其他
RS-485收发器的任意组合可以允许32个收发器或更少的
收发器连接在同一条总线上。MAX481/MAX483/MAX485
与MAX488-MAX491具有标准的12k〓接收器输入阻抗。
低功耗、限摆率、
RS-485/RS-422收发器
8 _______________________________________________________________________________________
MAX488
MAX490
TOP VIEW
1234
RODI
GND
8765
ABZY
VCC
DIP/SORD
Rt
Rt
VCC
5678
RODI
GND
4GND
DIRO
32
ABYZ
VCC
DR
R D
1
3VCC
4RO
2A
1
6578
GNDDIYZB
?MAX
MAX488
MAX490
NOTE: TYPICAL OPERATING CIRCUIT SHOWN WITH DIP/SO PACKAGE.
MAX489
MAX491
DIP/SO
TOP VIEW
Rt
Rt
DE VCC
RE GND
VCC RE
GND DE
RODI
9101211
BAZY
5
RONCDI
2
1, 8, 13
3 6, 7
144
1234567
141312111098
VCC
N.C.
N.C.ABZY
N.C.
ROREDEDI
GNDGND
R
D
D
RD
R
图2. MAX488/MAX490引脚配置与典型工作电路
图3. MAX489/MAX491引脚配置与典型工作电路
MAX483/MAX487/MAX488/MAX489:
降低EMI和反射
MAX483以及MAX487-MAX489 具有摆率限制,可以减
小EMI,并降低由不恰当的终端匹配电缆引起的反射。
图12 给出了驱动器输出波形以及使用 MAX481 、
MAX485、MAX490、MAX491或MAX1487发送150kHz
信号时的傅立叶
分析
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。有明显的大幅值高频谐波。
图13给出了MAX483、MAX487、MAX488或MAX489在
相同条件下发送数据时的测试结果。图 13中的高频谐波
幅值要低得多,因此,从根本上抑制了EMI。
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
_______________________________________________________________________________________ 9
RR
YZ
VOD
VOC
RECEIVER
OUTPUT
TEST POINT
1k〓
1k〓
S1S2
VCC
CRL
15pF
DI
DE
3V
YZ
CL1
CL2
AB
RO
RE
RDIFF
VID
OUTPUT
UNDER TEST
500〓 S1S2
VCC
CL
___________________________________________________________________ 测试电路
图4. 驱动器直流测试负载 图5. 接收器时序测试负载
图6. 驱动器/接收器时序测试电路 图7. 驱动器时序测试负载
MAX481/MAX483/MAX485/MAX487-MAX491/MAX1487
低功耗、限摆率、
RS-485/RS-422收发器
10 ______________________________________________________________________________________
___________________________________________________________________ 开关波形
DI
3V0V
ZY
VO
0V
-VO
VO
1.5V
tPLH
1/2 VO
10%
tR
90% 90%
tPHL
1.5V
1/2 VO
10%
tF
VDIFF = V (Y) - V (Z)
VDIFF
tSKEW = | tPLH - tPHL |
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
3V0V
Y, ZVOL
Y, Z
0V
1.5V 1.5V
VOL +0.5V
VOH -0.5V2.3V
2.3V
tZL(SHDN), tZL tLZ
tZH(SHDN), tZH tHZ
DE
VOH
VOLVID
-VID
1.5V
0V
1.5VOUTPUT
INPUT 0V
ROA-B
tPLHtPHL
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
3V0V
VCC
RORO
0V
1.5V 1.5V
VOL + 0.5V
VOH - 0.5V1.5V
1.5V
tZL(SHDN), tZL tLZ
tZH(SHDN), tZH tHZ
RE
_____________________________ 功能表(MAX481/MAX483/MAX485/MAX487/MAX1487)
图8. 驱动器传输延时 图9. 驱动器使能与禁用时序(MAX488与MAX490例外)
图10. 接收器传输延时 图11. 接收器使能与禁用时序(MAX488与MAX490例外)
表1. 发送 表2. 接收
INPUTS OUTPUT
RE DE A-B RO
0001
0000
> +0.2V
< -0.2V
Inputs open
X
101
High-Z*
X = Don't care
High-Z = High impedance* Shutdown mode for MAX481/MAX483/MAX487
INPUTS OUTPUTS
RE DE DI Z Y
XX01
1100
10XX
01
High-Z
High-Z*
10
High-Z
High-Z*
X = Don't care
High-Z = High impedance* Shutdown mode for MAX481/MAX483/MAX487
低功耗关断模式
(MAX481/MAX483/MAX487)
RE高电平、DE低电平使器件进入低功耗关断模式。驱动
器与接收器都被禁用时,器件才进入关断模式。关断模
式下,器件吸取电源电流的典型值为0.1?A。
可以同时驱动RE和DE;只要RE为高电平且DE为低电平
的持续时间小于50ns,可以确保这些器件不会进入关断
模式。若两个输入端维持这种状态至少600ns,则可确保
这些器件进入关断模式。
对于MAX481、MAX483与MAX487,tZH与tZL使能期间
假定器件并未处于低功耗关断状态 (MAX485 /MAX488-
MAX491 以及MAX1487 不能被关断)。在tZH(SHDN) 与
tZL(SHDN) 使能期间假定器件已被关断 (参见“电气特
性”)。
在低功耗关断状态下激活驱动器和接收器 (tZH(SHDN) ,
tZL(SHDN) )要比在工作模式下激活驱动器和接收器 (t ZH,
tZL)需要更长的时间。(若RE、DE输入等于逻辑0、1,
或1、1,或0、0,则这些器件处于工作模式。)
驱动器输出保护
可以通过两种机制避免由故障或总线冲突引起的过高的
输出电流与功耗。输出级的折返式电流限制在整个共模
电压范围(参见“典型