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參數(shù)資料
| 型號(hào)： | LTC489I |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Quad RS485 Line Receiver |
| 中文描述： | 485四線接收器 |
| 文件頁(yè)數(shù)： | 8/12頁(yè) |
| 文件大?。?/td> | 228K |
| 代理商： | LTC489I |
8
LTC488/LTC489
U
S
A
best to look at a driver connected to the end of the cable,
since this eliminates the possibility of getting reflections
from two directions. Simply look at the driver output while
transmitting square wave data. If the cable is terminated
properly, the waveform will look like a square wave
(Figure 8).
If the cable is loaded excessively (47
), the signal initially
sees the surge impedance of the cable and jumps to an
initial amplitude. The signal travels down the cable and is
reflected back out of phase because of the mistermination.
When the reflected signal returns to the driver, the ampli-
tude will be lowered. The width of the pedestal is equal to
twice the electrical length of the cable (about 1.5ns/foot).
If the cable is lightly loaded (470
), the signal reflects in
phase and increases the amplitude at the drive output. An
input frequency of 30kHz is adequate for tests out to 4000
ft. of cable.
O
PPLICATI
U
U
488/9 F08
DX
PROBE HERE
Rt = 120
Rt = 47
Rt = 470
Rt
RX
RECEIVER
DRIVER
Figure 8. Termination Effects
AC Cable Termination
Cable termination resistors are necessary to prevent un-
wanted reflections, but they consume power. The typical
differential output voltage of the driver is 2V when the
cable is terminated with two 120
resistors, causing
33mA of DC current to flow in the cable when no data is
being sent. This DC current is about 60 times greater than
the supply current of the LTC488/LTC489. One way to
eliminate the unwanted current is by AC coupling the
termination resistors as shown in Figure 9.
The coupling capacitor must allow high frequency energy
to flow to the termination, but block DC and low frequen-
cies. The dividing line between high and low frequency
depends on the length of the cable. The coupling capacitor
must pass frequencies above the point where the line
represents an electrical one-tenth wavelength. The value
of the coupling capacitor should therefore be set at 16.3pF
per foot of cable length for 120
cables. With the coupling
capacitors in place, power is consumed only on the signal
edges, and not when the driver output is idling at a 1 or 0
state. A 100nF capacitor is adequate for lines up to 4000
feet in length. Be aware that the power savings start to
decrease once the data rate surpasses 1/(120
)(
C).
488/9 F09
C = LINE LENGTH (FT)(16.3pF)
120
C
RX
RECEIVER
Figure 9. AC Coupled Termination
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| LTC491IN | Differential Driver and Receiver Pair |
| LTC491 | Differential Driver and Receiver Pair |
| LTC491C | Differential Driver and Receiver Pair |
| LTC491CN | Differential Driver and Receiver Pair |
| LTC491CS | Differential Driver and Receiver Pair |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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| LTC489IN | 功能描述:IC LINE RCVR RS485 QUAD 16-DIP RoHS:否 類(lèi)別:集成電路 (IC) >> 接口 - 驅(qū)動(dòng)器，接收器，收發(fā)器 系列:- 標(biāo)準(zhǔn)包裝:27 系列:- 類(lèi)型:收發(fā)器 驅(qū)動(dòng)器/接收器數(shù):3/3 規(guī)程:RS232，RS485 電源電壓:4.75 V ~ 5.25 V 安裝類(lèi)型:表面貼裝 封裝/外殼:28-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:28-SOIC 包裝:管件 |
| LTC489IN#PBF | 功能描述:IC LINE RCVR RS485 QUAD 16-DIP RoHS:是 類(lèi)別:集成電路 (IC) >> 接口 - 驅(qū)動(dòng)器，接收器，收發(fā)器 系列:- 標(biāo)準(zhǔn)包裝:27 系列:- 類(lèi)型:收發(fā)器 驅(qū)動(dòng)器/接收器數(shù):3/3 規(guī)程:RS232，RS485 電源電壓:4.75 V ~ 5.25 V 安裝類(lèi)型:表面貼裝 封裝/外殼:28-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:28-SOIC 包裝:管件 |
| LTC489INPBF | 制造商:Linear Technology 功能描述:RS-485 Quad Receiver 7mA 5V PDIP16 |
| LTC489ISW | 功能描述:IC LINE RCVR RS485 QUAD 16-SOIC RoHS:否 類(lèi)別:集成電路 (IC) >> 接口 - 驅(qū)動(dòng)器，接收器，收發(fā)器 系列:- 標(biāo)準(zhǔn)包裝:27 系列:- 類(lèi)型:收發(fā)器 驅(qū)動(dòng)器/接收器數(shù):3/3 規(guī)程:RS232，RS485 電源電壓:4.75 V ~ 5.25 V 安裝類(lèi)型:表面貼裝 封裝/外殼:28-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:28-SOIC 包裝:管件 |
| LTC489ISW#PBF | 功能描述:IC LINE RCVR RS485 QUAD 16-SOIC RoHS:是 類(lèi)別:集成電路 (IC) >> 接口 - 驅(qū)動(dòng)器，接收器，收發(fā)器 系列:- 產(chǎn)品培訓(xùn)模塊:RS-232 & USB Transceiver 標(biāo)準(zhǔn)包裝:2,000 系列:- 類(lèi)型:收發(fā)器 驅(qū)動(dòng)器/接收器數(shù):1/1 規(guī)程:RS232 電源電壓:3 V ~ 5.5 V 安裝類(lèi)型:表面貼裝 封裝/外殼:16-SSOP（0.209"，5.30mm 寬） 供應(yīng)商設(shè)備封裝:16-SSOP 包裝:帶卷 (TR) 其它名稱(chēng):296-19849-2 |
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