ETC LTC485

LTC485 - 低功率 RS485 接口收发器 - Linear Technology
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LTC485 - 低功率 RS485 接口收发器
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低功率：I CC = 300μA (典型值)
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专为 RS485 接口应用而设计
仿真
单 5V 电源
演示电路板
-7V 至 12V 总线共模范围允许总线上的器件之间存在 ±7V 的地电位差
热停机保护功能
通知
上电 / 断电无干扰驱动器输出允许进行收发器的带电插拔操作
技术支持
驱动器在三态或电源关断的情况下保持高阻抗
一个驱动器输出和接收器的组合阻抗允许在总线上连接多达 32 个收发器
70mV 典型输入迟滞
于 5ns 变化时的典型驱动器传播延迟为 30ns (用于高达 2.5MB 操作)
LTC2862 - 具 ±60V 故障保护功
引脚与具有 ±60V 电压保护能力的 LT1785 和 52Mbps LTC1685 相兼容
能的 3V 至 5.5V RS485 /
RS422 收发器
LTM2881 - 完整的隔离型
search
数据表
LTC485 - Low Power RS485 Interface
Transceiver
设计要点
DN102 - RS485 Transceivers Reduce
Power and EMI
DN39 - Low Power CMOS RS485
Transceiver
可靠性数据
R113 Reliability Data
产品选择卡
典型应用
RS485 Quick Guide
Ultra Rugged ±60V RS485
Transceivers
RS485 / RS422 uModule 收发
器和电源
描述
LTC® 485 是一款低功率差分总线 / 线路驱动器，专为多点数据传输标准 RS485 应用而
设计，具有扩展的共模范围 (12V 至 -7V)。它也符合 RS422 的要求。
与其双极型同类设计相比，CMOS 设计提供了显著的节能效果，而且并未牺牲针对过
载的 ESD 损害的坚固性。
驱动器和接收器具有三态输出，且驱动器输出在整个共模范围内保持高阻抗。热停机电
路用于防止由总线争用或故障所引起的过大功率消耗，该电路强制驱动器输出进入一种
高阻抗状态。
这款接收器具有一种故障保险功能，它可以在输入被置于开路状态时确保一种高输出状
态。
LTC485 具有完整的商业和扩展工业温度范围规格。
http://www.linear.com.cn/product/LTC485[2013-8-11 8:37:03]
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LTC485 - 低功率 RS485 接口收发器 - Linear Technology
应用
低功率 RS485 / RS422 驱动器
电平变换器
浏览此产品的人也参考
LTM2881 - 完整的隔离型 RS485 / RS422 uModule 收发器和电源
LT3080 - 可调 1.1A、单电阻、低压差稳压器
LT1785 - 具故障保护功能的 60V RS485/RS422 收发器
LT8610 - 具 2.5μA 静态电流的 42V、2.5A 同步降压型稳压器
LTC2862 - 具 ±60V 故障保护功能的 3V 至 5.5V RS485 / RS422 收发器
LT5400 - 四个匹配的电阻器网络
LT1763 - 500mA、低噪声、LDO 微功率稳压器
LTC4359 - 具反向输入保护功能的理想二极管控制器
LTC6992-1 / LTC6992-2 / LTC6992-3 / LTC6992-4 - TimerBlox : 电压控制型脉宽调制
器 (PWM)
LTC1799 - 采用电阻器设定 1kHz 至 33MHz 频率的 SOT-23 封装振荡器
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http://www.linear.com.cn/product/LTC485[2013-8-11 8:37:03]
LTC485
Low Power RS485
Interface Transceiver
Features
Description
n
n
n
The LTC®485 is a low power differential bus/line transceiver designed for multipoint data transmission standard
RS485 applications with extended common mode range
(12V to –7V). It also meets the requirements of RS422.
n
n
n
n
n
n
n
n
Low Power: ICC = 300μA Typ
Designed for RS485 Interface Applications
Single 5V supply
–7V to 12V Bus Common Mode Range Permits
±7V Ground Difference Between Devices on the Bus
Thermal Shutdown Protection
Power-Up/Down Glitch-Free Driver Outputs
Permit Live Insertion or Removal of Transceiver
Driver Maintains High Impedance in Three-State
or with the Power Off
Combined Impedance of a Driver Output and
Receiver Allows Up to 32 Transceivers on the Bus
70mV Typical Input Hysteresis
30ns Typical Driver Propagation Delays
with 5ns Skew for Up to 2.5MB Operation
Pin Compatible with ±60V Protected LT1785 and
52Mbps LTC1685
Applications
The CMOS design offers significant power savings over
its bipolar counterpart without sacrificing ruggedness
against overload of ESD damage.
The driver and receiver feature three-state outputs, with
the driver outputs maintaining high impedance over the
entire common mode range. Excessive power dissipation caused by bus contention or faults is prevented by a
thermal shutdown circuit which forces the driver outputs
into a high impedance state.
The receiver has a fail-safe feature which guarantees a
high output state when the inputs are left open.
The LTC485 is fully specified over the commercial and
extended industrial temperature range.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Low Power RS485/RS422 Transceiver
Level Translator
n
n
Typical Application
Driver Outputs
RO1
R
VCC1
RE1
Rt
DE1
DI1
RO2
D
R
A
GND1
VCC2
Rt
RE2
DE2
DI2
D
B
GND2
485 TA01a
485 TA01b
485fi
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LTC485
Absolute Maximum Ratings
Pin Configuration
(Note 1)
TOP VIEW
Supply Voltage...........................................................12V
Control Input Voltages......................–0.5V to VCC + 0.5V
Driver Input Voltage..........................–0.5V to VCC + 0.5V
Driver Output Voltage...............................................±14V
Receiver Input Voltage.............................................±14V
Receiver Output Voltages................. –0.5V to VCC + 0.5V
Operating Temperature Range
LTC485I......................................... –40°C ≤ TA ≤ 85°C
LTC485C............................................ 0°C ≤ TA ≤ 70°C
LTC485M..................................... –55°C ≤ TA ≤ 125°C
Lead Temperature (Soldering, 10 sec)................... 300°C
RO 1
R
RE 2
DE 3
D
DI 4
N8 PACKAGE
8-LEAD PLASTIC DIP
8
VCC
7
B
6
A
5
GND
S8 PACKAGE
8-LEAD PLASTIC SOIC
J8 PACKAGE
8-LEAD CERAMIC DIP
TJMAX = 125°C, θJA = 100°C/W (N)
TJMAX = 150°C, θJA = 150°C/W (S)
TJMAX = 155°C, θJA = 100°C/W (J)
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC485CN8#PBF
LTC485CN8#TRPBF
LTC485CN8
8-Lead Plastic DIP
0°C to 70°C
LTC485CS8#PBF
LTC485CS8#TRPBF
485
8-Lead Plastic SOIC
0°C to 70°C
LTC485IN8#PBF
LTC485IN8#TRPBF
LTC485IN8
8-Lead Plastic DIP
–40°C to 85°C
LTC485IS8#PBF
LTC485IS8#TRPBF
485I
8-Lead Plastic SOIC
–40°C to 85°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC485CN8
LTC485CN8#TR
LTC485CN8
8-Lead Plastic DIP
0°C to 70°C
LTC485CS8
LTC485CS8#TR
485
8-Lead Plastic SOIC
0°C to 70°C
LTC485IN8
LTC485IN8#TR
LTC485IN8
8-Lead Plastic DIP
–40°C to 85°C
LTC485IS8
LTC485IS8#TR
485I
8-Lead Plastic SOIC
–40°C to 85°C
LTC485MJ8
LTC485MJ8#TR
LTC485MJ8
8-Lead Ceramic DIP
–55°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
Electrical Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5%, unless otherwise noted. (Notes 2 and 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
VOD1
Differential Driver Output Voltage (Unloaded)
IO = 0
l
VOD2
Differential Driver Output Voltage (with Load)
R = 50Ω (RS422)
R = 27Ω (RS485), Figure 1
l
l
ΔVOD
Change in Magnitude of Driver Differential
Output Voltage for Complementary States
R = 27Ω or R = 50Ω, Figure 1
VOC
Driver Common Mode Output Voltage
Δ|VOC|
Change in Magnitude of Driver Common Mode
Output Voltage for Complementary States
TYP
MAX
5
2
1.5
UNITS
V
5
V
V
l
0.2
V
R = 27Ω or R = 50Ω, Figure 1
l
3
V
R = 27Ω or R = 50Ω, Figure 1
l
0.2
V
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LTC485
Electrical
Characteristics
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5%, unless otherwise noted. (Notes 2 and 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
VIH
Input High Voltage
DE, DI, RE
l
VIL
Input Low Voltage
DE, DI, RE
l
0.8
2
UNITS
V
V
IIN1
Input Current
DE, DI, RE
l
±2
μA
IIN2
Input Current (A, B)
DE = 0, VCC = 0V or 5.25V
VIN = 12V
VIN = –7V
l
l
±1
–0.8
mA
mA
VTH
Differential Input Threshold Voltage for Receiver –7V ≤ VCM ≤ 12V
l
0.2
V
ΔVTH
Receiver Input Hysteresis
VCM = 0V
l
VOH
Receiver Output High Voltage
IO = –4mA, VID = 200mV
l
–0.2
70
mV
3.5
V
VOL
Receiver Output Low Voltage
IO = 4mA, VID = –200mV
l
0.4
V
IOZR
Three-State (High Impedance) Output Current
at Receiver
VCC = Max, 0.4V ≤ VO ≤ 2.4V
l
±1
μA
RIN
Receiver Input Resistance
–7V ≤ VCM ≤ 12V
l
12
kΩ
Switching Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5%, unless otherwise noted. (Notes 2 and 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
ICC
Supply Current
No Load, Pins 2, 3, 4 = 0V or 5V
IOSD1
Driver Short-Circuit Current, VOUT = HIGH
VO = – 7V
l
IOSD2
Driver Short-Circuit Current, VOUT = LOW
VO = 10V
l
IOSR
Receiver Short-Circuit Current
0V ≤ VO ≤ VCC
l
7
tPLH
Driver Input to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF,
(Figures 3 and 5)
l
10
30
l
10
30
50
ns
5
10
ns
Outputs Enabled
Outputs Disabled
TYP
MAX
UNITS
500
300
900
500
μA
μA
35
100
250
mA
35
100
250
mA
85
mA
50
ns
l
l
tPHL
Driver Input to Output
tSKEW
Driver Output to Output
tr, tf
Driver Rise or Fall Time
15
25
ns
tZH
Driver Enable to Output High
CL = 100pF (Figures 4 and 6) S2 Closed
l
40
70
ns
tZL
Driver Enable to Output Low
CL = 100pF (Figures 4 and 6) S1 Closed
l
40
70
ns
tLZ
Driver Disable Time from Low
CL = 15pF (Figures 4 and 6) S1 Closed
l
40
70
ns
40
70
ns
90
200
ns
90
200
l
l
3
tHZ
Driver Disable Time from High
CL = 15pF (Figures 4 and 6) S2 Closed
l
tPLH
Receiver Input to Output
RDIFF = 54Ω, CL1 = CL2 = 100pF,
(Figures 3 and 7)
l
30
l
30
tPHL
tSKD
|tPLH – tPHL| Differential Receiver Skew
l
13
ns
ns
tZL
Receiver Enable to Output Low
CRL = 15pF (Figures 2 and 8) S1 Closed
l
20
50
ns
tZH
Receiver Enable to Output High
CRL = 15pF (Figures 2 and 8) S2 Closed
l
20
50
ns
tLZ
Receiver Disable from Low
CRL = 15pF (Figures 2 and 8) S1 Closed
l
20
50
ns
tHZ
Receiver Disable from High
CRL = 15pF (Figures 2 and 8) S2 Closed
l
20
50
ns
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All currents into device pins are positive; all currents out ot device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
Note 3: All typicals are given for VCC = 5V and TA = 25°C.
Note 4: The LTC485 is guaranteed by design to be functional over a supply
voltage range of 5V ±10%. Data sheet parameters are guaranteed over the
tested supply voltage range of 5V ±5%.
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LTC485
Typical Performance Characteristics
Receiver Output Low Voltage
vs Output Current
–18
TA = 25°C
32
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
24
20
16
12
8
4
0
0.5
0
4.4
–12
–10
–8
–6
3.2
4
3
OUTPUT VOLTAGE (V)
5
0.5
0.4
0.3
0.2
2.4
TA = 25°C
56
48
40
32
24
16
0
125
0
1
1.8
1.7
40
30
20
10
485 G07
25
50
0
75
TEMPERATURE (°C)
100
1.64
TA = 25°C
–84
–72
–60
–48
–36
–24
0
125
TTL Input Threshold
vs Temperature
–12
4
–25
485 G06
1.63
INPUT THRESHOLD VOLTAGE (V)
50
3
2
OUTPUT VOLTAGE (V)
1.9
1.5
–50
4
3
2
OUTPUT VOLTAGE (V)
–96
60
1
2.0
1.6
–108
70
0
2.1
Driver Output High Voltage
vs Output Current
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
80
125
2.2
485 G05
Driver Output Low Voltage
vs Output Current
TA = 25°C
100
RI = 54Ω
2.3
485 G04
90
25
50
0
75
TEMPERATURE (°C)
Driver Differential Output Voltage
vs Temperature
8
0.1
100
–25
485 G03
DIFFERENTIAL VOLTAGE (V)
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
0.7
0.6
0
3.0
–50
2
Driver Differential Output Voltage
vs Output Current
64
25
50
0
75
TEMPERATURE (°C)
3.6
–2
72
–25
3.8
485 G02
I = 8mA
0
–50
4.0
3.4
Receiver Output Low Voltage
vs Temperature
0.8
4.2
–4
485 G01
0.9
I = 8mA
4.6
–14
0
2.0
1.5
1.0
OUTPUT VOLTAGE (V)
4.8
TA = 25°C
–16
28
Receiver Output High Voltage
vs Temperature
OUTPUT VOLTAGE (V)
36
Receiver Output High Voltage
vs Output Current
0
1
3
2
OUTPUT VOLTAGE (V)
4
485 G08
1.62
1.61
1.60
1.59
1.58
1.57
1.56
1.55
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
125
485 G09
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LTC485
Typical Performance Characteristics
Driver Skew vs Temperature
Supply Current vs Temperature
5.4
640
7.0
4.8
580
6.5
4.2
520
6.0
3.6
5.5
5.0
3.0
2.4
4.5
1.8
4.0
1.2
3.5
0.6
3.0
–50
–25
25
50
0
75
TEMPERATURE (°C)
100
125
SUPPLY CURRENT (µA)
7.5
TIME (ns)
TIME (ns)
Receiver |tPLH – tPHL|
vs Temperature
0
–50
DRIVER ENABLED
460
400
340
DRIVER DISABLED
280
220
160
–25
25
50
0
75
TEMPERATURE (°C)
485 G10
100
125
100
–50
–25
0
25
50
75
TEMPERATURE (°C)
485 G11
100
125
485 G12
Pin Functions
RO (Pin 1): Receiver Output. If the receiver output is enabled (RE low), then if A > B by 200mV, RO will be high.
If A < B by 200mV, then RO will be low.
RE (Pin 2): Receiver Output Enable. A low enables the
receiver output, RO. A high input forces the receiver output
into a high impedance state.
DE (Pin 3): Driver Outputs Enable. A high on DE enables
the driver output. A and B, and the chip will function as a
line driver. A low input will force the driver outputs into a
high impedance state and the chip will function as a line
receiver.
DI (Pin 4): Driver Input. If the driver outputs are enabled
(DE high), then a low on DI forces the outputs A low and
B high. A high on DI with the driver outputs enabled will
force A high and B low.
GND (Pin 5): Ground Connection.
A (Pin 6): Driver Output/Receiver Input.
B (Pin 7): Driver Output/Receiver Input.
VCC (Pin 8): Positive Supply; 4.75 < VCC < 5.25.
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LTC485
Test Circuits
A
R
RECEIVER
OUTPUT
VOD
CRL
15pF
VOC
R
S1
TEST POINT
1k
1k
VCC
S2
485 F02
B
485 F01
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
3V
DE
A
DI
CL1
RDIFF
B
CL2
A
S1
RO
B
RE
VCC
500Ω
OUTPUT
UNDER TEST
S2
15pF
CL
485 F04
485 F03
Figure 3. Driver/Receiver Timing Test Circuit
Figure 4. Driver Timing Test Load #2
Switching Time Waveforms
3V
1.5V
DI
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
0V
tPLH
B
A
VO
0V
–VO
1.5V
1/2 VO
tPLH
VO
tSKEW
1/2 VO
10%
80%
tSKEW
90%
VDIFF = V(A) – V(B)
tr
20%
tf
485 F05
Figure 5. Driver Propagation Delays
485fi
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LTC485
Switching Time Waveforms
3V
1.5V
DI
tLZ
tZL
5V
A, B
2.3V
OUTPUT NORMALLY LOW
0.5V
2.3V
OUTPUT NORMALLY HIGH
0.5V
VOL
A, B
1.5V
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
0V
VOH
0V
tHZ
tZH
485 F06
Figure 6. Driver Enable and Disable Times
R
VOH
1.5V
VOL
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
tPHL
VOD2
A, B
–VOD2
0V
1.5V
OUTPUT
tPLH
INPUT
485 F07
Figure 7. Receiver Propagation Delays
3V
1.5V
RE
R
tLZ
tZL
5V
R
0V
1.5V
f = 1MHz, tr ≤ 10ns, tf ≤ 10ns
0V
1.5V
OUTPUT NORMALLY LOW
0.5V
1.5V
OUTPUT NORMALLY HIGH
0.5V
tHZ
tZH
485 F08
Figure 8. Receiver Enable and Disable Times
Function Tables
LTC485 Receiving
LTC485 Transmitting
INPUTS
INPUTS
OUTPUTS
OUTPUTS
RE
DE
DI
LINE
CONDITION
X
1
1
No Fault
X
1
0
No Fault
1
0
0
0
≤ –0.2V
0
X
0
X
X
Z
Z
0
0
Inputs Open
1
X
1
X
Fault
Z
Z
1
0
X
Z
B
0
A
RE
DE
A–B
R
1
0
0
≥ 0.2V
1
485fi
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LTC485
Applications Information
Basic Theory of Operation
Previous RS485 transceivers have been designed using
bipolar technology because the common mode range
of the device must extend beyond the supplies and the
device must be immune to ESD damage and latchup.
Unfortunately, the bipolar devices draw a large amount of
supply current, which is unacceptable for the numerous
applications that require low power consumption. The
LTC485 is the first CMOS RS485/RS422 transceiver which
features ultralow power consumption without sacrificing
ESD and latchup immunity.
The LTC485 uses a proprietary driver output stage, which
allows a common-mode range that extends beyond the
power supplies while virtually eliminating latchup and
providing excellent ESD protection. Figure 9 shows the
LTC485 output stage while Figure 10 shows a conventional
CMOS output stage.
When the conventional CMOS output stage of Figure 10
enters a high impedance state, both the P-channel (P1)
and the N-channel (N1) are turned off. If the output is
then driven above VCC or below ground, the P + /N-well
diode (D1) or the N + /P-substrate diode (D2) respectively
will turn on and clamp the output to the supply. Thus,
the output stage is no longer in a high impedance state
and is not able to meet the RS485 common mode range
requirement. In addition, the large amount of current
flowing through either diode will induce the well known
CMOS latchup condition, which could destroy the device.
The LTC485 output stage of Figure 9 eliminates these
problems by adding two Schottky diodes, SD3 and SD4.
The Schottky diodes are fabricated by a proprietary modification to the standard N-well CMOS process. When the
output stage is operating normally, the Schottky diodes
are forward biased and have a small voltage drop across
them. When the output is in the high impedance state and
is driven above VCC or below ground, the parasitic diodes
D1 or D2 still turn on, but SD3 or SD4 will reverse bias
and prevent current from flowing into the N-well or the
substrate. Thus, the high impedance state is maintained
even with the output voltage beyond the supplies. With
no minority carrier current flowing into the N-well or
substrate, latchup is virtually eliminated under power-up
or power-down conditions.
VCC
VCC
SD3
P1
P1
D1
OUTPUT
LOGIC
SD4
N1
D1
N1
D2
485 F09
Figure 9. LTC485 Output Stage
OUTPUT
LOGIC
D2
485 F10
Figure 10. Conventional CMOS Output Stage
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LTC485
Applications Information
The LTC485 output stage will maintain a high impedance
state until the breakdown of the N-channel or P-channel
is reached when going positive or negative respectively.
The output will be clamped to either VCC or ground by a
Zener voltage plus a Schottky diode drop, but this voltage
is way beyond the RS485 operating range. This clamp
protects the MOS gates from ESD voltages well over
2000V. Because the ESD injected current in the N-well or
substrate consists of majority carriers, latchup is prevented
by careful layout techniques.
Propagation Delay
Many digital encoding schemes are dependent upon the
difference in the propagation delay times of the driver and
the receiver. Using the test circuit of Figure 13, Figures 11
and 12 show the typical LTC485 receiver propagation delay.
The receiver delay times are:
|tPLH – tPHL| = 9ns Typ, VCC = 5V
The driver skew times are:
Skew = 5ns Typ, VCC = 5V
10ns Max, VCC = 5V, TA = –40°C to 85°C
A
A
DRIVER
OUTPUTS
DRIVER
OUTPUTS
B
RECEIVER
RO
OUTPUTS
B
RECEIVER
RO
OUTPUTS
485 F11
485 F12
Figure 11. Receiver tPHL
Figure 12. Receiver tPLH
100pF
TTL IN
tr, tf < 6ns
D
BR
R
R
100Ω
RECEIVER
OUT
485 F13
100pF
Figure 13. Receiver Propagation Delay Test Circuit
485fi
9
LTC485
Applications Information
LTC485 Line Length vs Data Rate
The maximum line length allowable for the RS422/RS485
standard is 4000 feet.
Figures 17 and 18 show that the LTC485 is able to comfortably drive 4000 feet of wire at 110kHz.
100Ω
C
A
LTC485
D
B
NOISE
GENERATOR
TTL
IN
RO
LTC485
TTL
OUT
COMMON MODE
VOLTAGE (A + B)/2
4000 FT 26AWG
TWISTED PAIR
DI
485 F14
Figure 14. Line Length Test Circuit
485 F17
Figure 17. System Common Mode Voltage at 110kHz
Using the test circuit in Figure 14, Figures 15 and 16 show
that with ~20VP-P common mode noise injected on the
line, The LTC485 is able to reconstruct the data stream at
the end of 4000 feet of twisted pair wire.
RO
COMMON MODE
VOLTAGE (A – B)
DI
RO
COMMON MODE
VOLTAGE (A + B)/2
485 F18
Figure 18. System Differential Voltage at 110kHz
DI
485 F15
When specifying line length vs maximum data rate the
curve in Figure 19 should be used.
Figure 15. System Common Mode Voltage at 19.2kHz
CABLE LENGTH (FT)
10k
RO
DIFFERENTIAL
VOLTAGE A – B
1k
100
DI
10
10k
485 F16
Figure 16. System Differential Voltage at 19.2kHz
100k
1M 2.5M
MAXIMUM DATA RATE
10M
485 F19
Figure 19. Cable Length vs Maximum Data Rate
485fi
10
LTC485
Typical Application
Typical RS485 Network
Rt
Rt
485 TA02
Package Description
J8 Package
8-Lead CERDIP (Narrow .300 Inch, Hermetic)
(Reference LTC DWG # 05-08-1110)
CORNER LEADS OPTION
(4 PLCS)
.023 – .045
(0.584 – 1.143)
HALF LEAD
OPTION
.045 – .068
(1.143 – 1.650)
FULL LEAD
OPTION
.005
(0.127)
MIN
.405
(10.287)
MAX
8
7
6
5
.025
(0.635)
RAD TYP
.220 – .310
(5.588 – 7.874)
1
.300 BSC
(7.62 BSC)
2
3
4
.200
(5.080)
MAX
.015 – .060
(0.381 – 1.524)
.008 – .018
(0.203 – 0.457)
0° – 15°
NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE
OR TIN PLATE LEADS
.045 – .065
(1.143 – 1.651)
.014 – .026
(0.360 – 0.660)
.100
(2.54)
BSC
.125
3.175
MIN
J8 0801
485fi
11
LTC485
Package Description
N8 Package
8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
.400*
(10.160)
MAX
8
7
6
.300 – .325
(7.620 – 8.255)
5
.255 .015*
(6.477 0.381)
.065
(1.651)
TYP
.008 – .015
(0.203 – 0.381)
1
2
4
3
(
+.035
.325 –.015
8.255
+0.889
–0.381
.130 .005
(3.302 0.127)
.045 – .065
(1.143 – 1.651)
)
.120
(3.048) .020
MIN
(0.508)
MIN
.018 .003
(0.457 0.076)
.100
(2.54)
BSC
N8 1002
NOTE:
1. DIMENSIONS ARE
INCHES
MILLIMETERS
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.050 BSC
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
8
.245
MIN
.160 ±.005
.010 – .020
× 45°
(0.254 – 0.508)
NOTE:
1. DIMENSIONS IN
5
.150 – .157
(3.810 – 3.988)
NOTE 3
1
RECOMMENDED SOLDER PAD LAYOUT
.053 – .069
(1.346 – 1.752)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
6
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
.008 – .010
(0.203 – 0.254)
7
.014 – .019
(0.355 – 0.483)
TYP
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
2
3
4
.004 – .010
(0.101 – 0.254)
.050
(1.270)
BSC
SO8 0303
485fi
12
LTC485
Revision History
(Revision history begins at Rev I)
REV
DATE
DESCRIPTION
PAGE NUMBER
I
4/11
Removed lead free version of LTC485MJ8 from Order Information section.
2
485fi
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
13
LTC485
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
LTC486/LTC487
Low Power Quad RS485 Drivers
110μA Supply Current
LTC488/LTC489
Low Power Quad RS485 Receivers
7mA Supply Current
LTC490/LTC491
Low Power Full-Duplex RS485 Transceivers
300μA Supply Current
LTC1480
3.3V Supply RS485 Transceiver
Lower Supply Voltage
LTC1481
Low Power RS485 Transceiver with Shutdown
Lowest Power
LTC1482
RS485 Transceiver with Carrier Detect
±15kV ESD, Fail-Safe
LTC1483
Low Power, Low EMI RS485 Transceiver
Slew Rate Limited Driver Outputs, Lowest Power
LTC1484
RS485 Transceiver with Fail-Safe
±15kV ESD, MSOP Package
LTC1485
10Mbps RS485 Transceiver
High Speed
LTC1518/LTC1519
52Mbps Quad RS485 Receivers
Higher Speed, LTC488/LTC489 Pin-Compatible
LTC1520
LVDS-Compatible Quad Receiver
100mV Threshold, Low Channel-to-Channel Skew
LTC1535
2500V Isolated RS485 Transceiver
Full-Duplex, Self-Powered Using External Transformer
LTC1685
52Mbps RS485 Transceiver
Industry-Standard Pinout, 500ps Propagation Delay Skew
LTC1686/LTC1687
52Mbps Full-Duplex RS485 Transceivers
LTC490/LTC491 Pin Compatible
LTC1688/LTC1689
100Mbps Quad RS485 Drivers
Highest Speed, LTC486/LTC487 Pin Compatible
LTC1690
Full-Duplex RS485 Transceiver with Fail-Safe
±15kV ESD, LTC490 Pin Compatible
LT1785/LTC1785A
±60V Protected RS485 Transceivers
±15kV ESD, Fail-Safe (LT1785A)
LT1791/LTC1791A
±60V Protected Full-Duplex RS485 Transceivers
±15kV ESD, Fail-Safe (LT1791A)
LTC2850/LTC2851/
LTC2852
3.3V Supply RS485 Transceivers
±15kV ESD, 20Mbps, 900µA Supply Current, Fail-Safe
LTC2854/LTC2855
3.3V Supply RS485 Transceivers
±15kV ESD, 20Mbps, 900µA Supply Current,
Integrated Switchable Termination
LTC2856/LTC2857/
LTC2858
20Mbps RS485 Transceivers
±15kV ESD, 900µA Supply Current, Fail-Safe
LTC2859/LTC2861
20Mbps RS485 Transceivers
±15kV ESD, 900µA Supply Current, Integrated Switchable Termination
485fi
14 Linear Technology Corporation
LT 0411 REV I • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 l FAX: (408) 434-0507
l
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 1994
advertisement
RS485 Transceivers Reduce Power and EMI – Design Note 102
Dave Dwelley, Teo Yang Long, Yau Khai Cheong and Bob Reay
SHUTDOWN
RO
VCC
R
B
RE
20
10
A
RB
0
–10
–20
–30
–40
–50
–60
–70
RA
DE
DI
LTC1483
The LTC1483 is a reduced EMI version of the LTC1481
intended for use in systems where electromagnetic interference concerns take precedence over high data rates.
The LTC1483 driver slew rate is deliberately limited to
reduce the high frequency electromagnetic emissions
(Figures 2a and 2b) while improving signal fidelity by
reducing reflections due to misterminated cables. The
LOG MAGNITUDE (dBVRMS)
Recent innovations in process and circuit design have
enabled the release of three new RS485 transceivers: the
LTC®1481, LTC1483 and LTC1487. These devices share
an improved receiver circuit which features 80µA quiescent current operation (driver disabled) with no loss in AC
performance relative to standard RS485 devices, and a
new 1µA shutdown mode (Figure 1). All three new devices
are pin compatible with the industry standard LTC485
pinout, and feature Linear Technology’s exclusive ±10kV
ESD protection (Human Body Model) at the line I/O pins,
eliminating the need for external ESD protection in most
cases.
–80
0
GND
D
1
2
3
4
5
FREQUENCY (MHz)
DN102 • F01
Figure 2a. Typical RS485 Driver Output Spectrum
Transmitting at 150kHz
RA, RB:
LTC1481/LTC1483 = 12k (MIN)
LTC1487 = 96k (TYP)
20
Figure 1. LTC1481/LTC1483/LTC1487 Block Diagram
LOG MAGNITUDE (dBVRMS)
LTC1481
The LTC1481 provides full 2.5Mbaud driver and receiver
speeds with the low power and improved ruggedness
features shared by all three members of the family. Like all
Linear Technology RS485 products, it features full RS485
and RS422 compatibility, guaranteed operation over the
– 7V to 12V common-mode range and a unique driver
output circuit that prevents CMOS latch-up and maintains
high impedance at the line pins, even when the power is
off. An internal driver short-circuit current limit and a
thermal overload protection circuit prevent damage under
severe fault conditions. The LTC1481 is ideally suited for
designs which need to transmit high speed data with
minimum power consumption.
10
0
–10
–20
–30
–40
–50
–60
–70
–80
0
1
2
3
4
5
FREQUENCY (MHz)
Figure 2b. Slew Rate Limited LTC1483 Driver Output
Spectrum Transmitting at 150kHz
, LTC and LT are registered trademarks of Linear Technology Corporation.
04/95/102
maximum operating frequency of the LTC1483 driver is
limited to 250kbaud. All other performance parameters are
unchanged from the LTC1481, including the low power
receiver operation and the 1µA shutdown mode.
LTC1487
The LTC1487 shares the low power and low slew rate
features of the LTC1483. Additionally, the LTC1487 is
designed with a high input impedance of 96kΩ (typical) to
allow up to 256 transceivers to share a single RS485
differential data line. This exceptionally high input impedance enables additional transceivers to be connected to a
single RS485 line, reducing cabling costs and complexity
in systems with many nodes.
The RS485 specification requires that a transceiver be able
to drive as many as 32 “unit loads.” One unit load (UL) is
defined as an impedance that draws a maximum of 1mA
with up to 12V across it. Most standard RS485 transceiv-
ers, including the LTC1481 and LTC1483, have an input
resistance of approximately 12k, equivalent to 1UL, which
limits a single RS485 bus to 32 nodes. With its high 96kΩ
input impedance, the LTC1487 presents only 0.125UL to
the line, allowing up to 256 transceivers (32UL/0.125UL =
256) to be connected to the data bus line without overloading the driver (Figure 3).
Conclusions
The LTC1481, LTC1483 and LTC1487 make up the third
generation of the Linear Technology CMOS RS485 transceiver family, all started by the original CMOS RS485
transceiver, the LTC485. These three new devices put
exceptional ruggedness features and the lowest power
operation available in the industry into three unique niches
in the RS485 market: high performance (LTC1481), low
EMI (LTC1483) and high input impedance (LTC1487).
RO
RO
DI
DI
120Ω
LTC1481/LTC1483: UP TO 32 TRANSCEIVERS
LTC1487: UP TO 256 TRANSCEIVERS
120Ω
DN102 • F03
Figure 3. Mulitple Transceivers On One RS485 Bus
For literature on our RS485 Transceivers,
call 1-800-4-LINEAR. For applications help,
call (408) 432-1900, Ext. 453
Linear Technology Corporation
LT/GP 0495 160K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1995
RS485 Quick Guide
TIA/EIA-485-A Standard
RS485 conveys data differentially over a terminated twisted pair, permitting up to 10Mbps data rates. The standard specifies electrical
characteristics of a driver and receiver, and does not specify any data protocol or connectors. RS485 is popular for inexpensive local
networks, multidrop communication links and long haul data transfer over distances of up to 4,000 feet. The use of a balanced line means
RS485 has excellent noise rejection and is ideal for industrial and commercial applications. You’ll find RS485 in applications as diverse as
monitoring oil wells and linking POS terminals, to alarm systems, motion control and HVAC controls. Extended capability transceivers offer data
rates up to 100Mbps and up to 256 nodes, as well as 2500VRMS isolation and fault protection up to ±60V.
Specification
RS422
RS485
Differential
Differential
1 Driver,
10 Receivers
32 Drivers,
32 Receivers
4000 Feet
4000 Feet
10Mbps
10Mbps
–0.25V to 6V
–7V to 12V
Minimum Loaded
±2V
±1.5V
Maximum Unloaded
±5V
±5V
100Ω
120Ω
Mode of Operation
Number of Drivers and Receivers
Allowed on One Line
Maximum Cable Length
Maximum Data Rate
Maximum Voltage Applied to Driver Output
Differential Driver Output Signal
Termination
Receiver Input Voltage Range
±7V
–7V to 12V
Receiver Input Sensitivity
±200mV
±200mV
Receiver Input Resistance
4kΩ (Min)
12kΩ (Min)
What is the Failsafe Receiver Output State with No Input Signal?
That depends on the failsafe type of the receiver. Type 1 devices (see over) output
a guaranteed 1 state when the receiver inputs are left open, but the output is
undetermined when the inputs are shorted. Type 2 devices output a guaranteed 1
state whether the receiver inputs are left open, shorted or terminated but not driven.
What is the Proper Way to Terminate the Cable?
The cable should be terminated at each end with a resistance equal to
characteristic impedance.
L, LT, LTC, LTM, Linear Technology and the Linear logo are
registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
10k
CABLE LENGTH (FT)
What Distance Can Be Achieved?
The achievable distance is a function of the cable. The longer the cable, the greater
the attenuation. Because attenuation increases with frequency, cables also exhibit a
lowpass filter behavior so that achievable distance diminishes with data rate.
The distances recommended by the RS485 standard are shown in the graph to the
right. Many cables are capable of higher speed and distance. Consult the cable
manufacturer’s typical performance curve of 0 to 50% rise time vs cable length.
1k
100
10
10k
RS485
SPECIFIED
LIMITS
PRACTICAL
LIMIT FOR
20Mbps
DEVICES
100k
1M
10M
DATA RATE (bps)
100M
Linear Technology RS485/RS422 Transceivers
Part Number
Supply
Max Data
ESD
(V)
Rate (Bits/s) # Dr # Rec Duplex SHDN (kV) Failsafe Comments
Temp
Grade
Package
2500VRMS Isolation
LTM®2881-3/-5
LTC1535
3.3/5
20M
1
1
Full
Yes
±15
Type 2
No External Components
Required, Isolated 1W DC/DC
Converter, Switchable, 120Ω
Termination, UL File #E151738
5
250k
1
1
Full
No
±8
Type 2
UL File #E151738
Pin-Compatible with LT1785A
C, I, H, MP
C, I
15 × 11.25 × 2.8 LGA,
15 × 11.25 × 3.4 BGA
SO(W)-28
±60V Fault Protection
LTC2862-1/-2
3 to 5.5
20M/250k
1
1
Half
Yes
±15
Type 2
LTC2863-1/-2
3 to 5.5
20M/250k
1
1
Full
No
±15
Type 2
C, I, H, MP
SO-8, 3 × 3 DFN-8
C, I, H, MP
SO-8, 3 × 3 DFN-8
LTC2864-1/-2
3 to 5.5
20M/250k
1
1
Full
Yes
±15
Type 2
Pin-Compatible with LT1791A
LTC2865
3 to 5.5
20M/250k
1
1
Full
Yes
±15
Type 2
Logic Supply Pin, SLO Pin
C, I, H
LT1785A
5
250k
1
1
Half
Yes
±15
Type 2
Pin-Compatible with LTC485
C, I, H
SO-8, DIP-8
LT1791A
5
250k
1
1
Full
Yes
±15
Type 2
Pin-Compatible with LTC491
C, I, H
SO-14, DIP-14
3 × 3 DFN-10
C, I, H, MP
SO-14, 3 × 3 DFN-10
MSOP-12, 4 × 3 DFN-12
Integrated Switchable 120Ω Termination
LTC2854
3.3
20M
1
1
Half
Yes
±25
Type 2
Low Power
C, I, H
LTC2859
5
20M/250k
1
1
Half
Yes
±15
Type 2
Slew Rate Control, Low Power
C, I, H
3 × 3 DFN-10
LTC2855
3.3
20M
1
1
Full
Yes
±15
Type 2
Low Power
C, I, H
4 × 3 DFN-12, SSOP-16
LTC2861
5
20M/250k
1
1
Full
Yes
±15
Type 2
Slew Rate Control, Low Power
C, I
4 × 3 DFN-12, SSOP-16
3.3V Supply Operation
LTC2850
3.3
20M
1
1
Half
Yes
±15
Type 2
Low Power
C, I, H
SO-8, MSOP-8, 3 × 3 DFN-8
LTC2851
3.3
20M
1
1
Full
No
±15
Type 2
Low Power
C, I, H
SO-8, MSOP-8, 3 × 3 DFN-8
C, I, H
SO-14, MSOP-10, 3 × 3 DFN-10
LTC2852
3.3
20M
1
1
Full
Yes
±15
Type 2
DE and RE Pins, Low Power
LTC1480
3.3
2.5M
1
1
Half
Yes
±3.5
Type 1
Low Power
C, I
SO-8, DIP- 8
Low Power
LTC2856-1/-2
5
20M/250k
1
1
Half
Yes
±15
Type 2
Hot Swap™ Capable
C, I, H
LTC2857-1/-2
5
20M/250k
1
1
Full
No
±15
Type 2
Hot Swap Capable
C, I, H
MSOP-8, 3 × 3 DFN-8
LTC2858-1/-2
5
20M/250k
1
1
Full
Yes
±15
Type 2
Hot Swap Capable
C, I, H
MSOP-10, 3 × 3 DFN-10
LTC1690
5
5M
1
1
Full
No
±15
Type 2
C, I
LTC1481
5
2.5M
1
1
Half
Yes
±10
Type 1
C, I
SO-8, DIP-8
LTC1482
5
4M
1
1
Half
Yes
±15
Type 2
Carrier Detect
C, I
MSOP-8, SO-8, DIP-8
LTC1483
5
150k
1
1
Half
Yes
±10
Type 1
Low EMI
C, I
SO-8, DIP-8
LTC1484
5
4M
1
1
Half
Yes
±15
Type 2
C, I
MSOP-8, SO-8, DIP-8
LTC1485
5
10M
1
1
Half
No
±10
Type 1
C, I
SO-8, DIP-8
LTC1487
5
250k
1
1
Half
Yes
±10
Type 1
LTC485
5
2.5M
1
1
Half
No
±4
Type 1
LTC490
5
2.5M
1
1
Full
No
±10
Type 1
LTC491
5
2.5M
1
1
Full
No
±10
Type 1
Low EMI
C
C, I, M
DE and RE Pins
MSOP-8, 3 × 3 DFN-8
MSOP-8, SO-8, DIP-8
SO-8, DIP-8
SO-8, DIP-8, CERDIP-8
C, I
SO-8, DIP-8
C, I
SO-14, DIP-14
High Speed
LTC1685
5
52M
1
1
Half
No
±4
Type 2
C, I
SO-8
LTC1686
5
52M
1
1
Full
No
±4
Type 1
C, I
SO-8
LTC1687
5
52M
Quad Drivers and Receivers
1
1
Full
No
±4
Type 1
DE and RE Pins
C, I
SO-14
LTC1688/89
5
100M
LTC486/87
5
10M
LTC1518/19
5
52M
LTC488/89
5
10M
LTC1520
5
50M
RS232/RS485 Multiprotocol
4
4
0
0
0
0
0
4
4
4
No
No
No
No
No
±4
±4
±4
±10
±4
Type 1
Type 2
Type 1
Hot Swap Capable, 1/2 DE Pins
Low Power, 1/2 DE Pins
C, I
C, I
C, I
C, I
C
SO-16
SO(W)-16, DIP-16
SO-16
SO(W)-16, DIP-16
SO-16
1/2 DE Pins
High Speed, LVDS-Compatible
LTC2870
3 to 5.5
20M/500k
1
1
Both
Yes
±26
Type 2
Two RS232 Transceivers
C, I
4 × 5 QFN-28, TSSOP-28
LTC2871
3 to 5.5
20M/500k
1
1
Both
Yes
±16
Type 2
Two RS232 Transceivers
C, I
5 × 7 QFN-38, TSSOP-38
LTC2872
3 to 5.5
20M/500k
2
2
Both
Yes
±16
Type 2
Four RS232 Transceivers
C, I
5 × 7 QFN-38
Type 1 = Open; Type 2 = Idle, Open, Short
www.linear.com/RS485 n 1-800-4-LINEAR
0313D