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| 型号： | SN75HVD08 |
| 厂商： | Texas Instruments, Inc. |
| 英文描述： | 3.3/5-V RS-485 Transceiver |
| 中文描述： | 3.3/5V RS-485 收发器 |
| 文件页数： | 2/14页 |
| 文件大小： | 290K |
| 代理商： | SN75HVD08 |
www.ti.com
APPLICATION INFORMATION
OPTO-ISOLATED DATA BUSES
SUPPLY SOURCE IMPEDANCE
+
–
+
–
VS
RS
IL
RL
VL = VS – 2RSIL
DC-to-DC
Converter
Opto
Isolators
DC-to-DC
Converter
Opto
Isolators
Local Power
Source
Rest of
Board
Local Power
Source
Rest of
Board
SN75HVD08, SN65HVD08
SLLS550A – NOVEMBER 2002 – REVISED MAY 2003
As electrical loads are physically distanced from their
power source, the effects of supply and return line
Under dynamic load requirements, the distributed
impedance and the resultant voltage drop must be
inductance and capacitance of the power lines may
accounted. If the supply regulation at the load cannot
not be ignored and decoupling capacitance at the
be maintained to the circuit requirements, it forces the
load is required. The amount depends upon the
use of remote sensing, additional regulation at the
magnitude and frequency of the load current change
load, bigger or shorter cables, or a combination of
but, if only powering the SN65HVD08, a 0.1 F
these. The SN65HVD08 eases this problem by re-
ceramic capacitor is usually sufficient.
laxing the supply requirements to allow for more
variation in the supply voltage over typical RS-485
transceivers.
Long RS-485 circuits can create large ground loops
and pick up common-mode noise voltages in excess
of the range tolerated by standard RS-485 circuits. A
In the steady state, the voltage drop from the source
common remedy is to provide galvanic isolation of the
to the load is simply the wire resistance times the
data circuit from earth or local grounds.
load current as modeled in Figure 13.
Transformers, capacitors, or phototransistors most
often provide isolation of the bus and the local node.
Transformers and capacitors require changing signals
to transfer the information over the isolation barrier
and
phototransistors
(opto-isolators)
can
pass
steady-state signals. Each of these methods incurs
additional costs and complexity, the former in clock
encoding and decoding of the data stream and the
latter in requiring an isolated power supply.
Quite often, the cost of isolated power is repeated at
Figure 13. Steady-State Circuit Model
each node connected to the bus as shown in Fig-
ure 14. The possibly lower-cost solution is to gener-
For example, if you were to provide 5-V
±5% supply
ate this supply once within the system and then
power to a remote circuit with a maximum load
distribute it along with the data line(s) as shown in
requirement of 0.1 A (one SN65HVD08), the voltage
at the load would fall below the 4.5-V minimum of
most 5-V circuits with as little as 5.8 m of 28-GA
conductors. Table 1 summarizes wire resistance and
the length for 4.5 V and 3 V at the load with 0.1 A of
load current. The maximum lengths would scale
linearly for higher or lower load currents.
Table 1. Maximum Cable Lengths for Minimum
Load Voltages at 0.1 A Load
WIRE
RESISTANCE
4.5 V LENGTH
3-v LENGTH
SIZE
AT 0.1 A
28 Gage
0.213
/m
5.8 m
41.1 m
24 Gage
0.079
/m
15.8 m
110.7 m
22 Gage
0.054
/m
23.1 m
162.0 m
20 Gage
0.034
/m
36.8 m
257.3 m
18 Gage
0.021
/m
59.5 m
416.7 m
Figure 14. Isolated Power at Each Node
10
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相关代理商/技术参数 |
参数描述 |
|---|---|
| SN75HVD08D | 功能描述:RS-485接口IC 3.3/5-V RS-485 Transceiver RoHS:否 制造商:Texas Instruments 数据速率:250 Kbps 工作电源电压:3.3 V 电源电流:750 uA 工作温度范围:- 40 C to + 125 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Tube |
| SN75HVD08DG4 | 功能描述:总线收发器 3.3/5-V RS-485 Transceiver RoHS:否 制造商:Fairchild Semiconductor 逻辑类型:CMOS 逻辑系列:74VCX 每芯片的通道数量:16 输入电平:CMOS 输出电平:CMOS 输出类型:3-State 高电平输出电流:- 24 mA 低电平输出电流:24 mA 传播延迟时间:6.2 ns 电源电压-最大:2.7 V, 3.6 V 电源电压-最小:1.65 V, 2.3 V 最大工作温度:+ 85 C 封装 / 箱体:TSSOP-48 封装:Reel |
| SN75HVD08DR | 功能描述:RS-485接口IC 3.3/5-V RS-485 Transceiver RoHS:否 制造商:Texas Instruments 数据速率:250 Kbps 工作电源电压:3.3 V 电源电流:750 uA 工作温度范围:- 40 C to + 125 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Tube |
| SN75HVD08DRG4 | 功能描述:总线收发器 3.3/5-V RS-485 Transceiver RoHS:否 制造商:Fairchild Semiconductor 逻辑类型:CMOS 逻辑系列:74VCX 每芯片的通道数量:16 输入电平:CMOS 输出电平:CMOS 输出类型:3-State 高电平输出电流:- 24 mA 低电平输出电流:24 mA 传播延迟时间:6.2 ns 电源电压-最大:2.7 V, 3.6 V 电源电压-最小:1.65 V, 2.3 V 最大工作温度:+ 85 C 封装 / 箱体:TSSOP-48 封装:Reel |
| SN75HVD08P | 功能描述:RS-485接口IC 3.3/5-V RS-485 Transceiver RoHS:否 制造商:Texas Instruments 数据速率:250 Kbps 工作电源电压:3.3 V 电源电流:750 uA 工作温度范围:- 40 C to + 125 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Tube |
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