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參數(shù)資料
| 型號： | NM485SLC |
| 廠商： | Murata Power Solutions Inc |
| 文件頁數(shù)： | 4/5頁 |
| 文件大?。?/td> | 0K |
| 描述： | ISOLATED INTERFACE LP EIA-485 |
| 標準包裝： | 15 |
| 系列： | IsoLoop® |
| 類型： | 收發(fā)器，隔離式 |
| 驅(qū)動器/接收器數(shù)： | 1/1 |
| 規(guī)程： | RS485 |
| 電源電壓： | 4.75 V ~ 5.25 V |
| 安裝類型： | 通孔 |
| 封裝/外殼： | 24-DIP（0.667"，16.95mm） |
| 供應商設備封裝： | 24-DIL |
| 包裝： | 管件 |
| 產(chǎn)品目錄頁面： | 2721 (CN2011-ZH PDF) |
| 其它名稱： | 811-1446-5 |
NM485SLC
Low Power Isolated EIA-485 Driver and Receiver
KDC_NM485SLC.A04 Page 4 of 5
www.murata-ps.com/support
APPLICATION NOTES (continued)
System Performance
The EIA-485 standard allows a maximum of 32 unit loads to be connected to the network, this is less than the LONWORKS standard of 64 nodes. A unit load is any single
driver, receiver or transceiver in the EIA-485 standard, or any single node under the LONWORKS scheme. Similarly the EIA-485 standard species a maximum data rate
standard of 10Mbps, whereas the maximum LONWORKS data rate standard is 1.25Mbps. The resultant maximum system performance for the LONWORKS EIA-485 con-
guration is therefore 32 nodes at 1.25Mbps. The NM485SLC isolated serial interface device supports this conguration, as well as any lower specied system.
The EIA-485 standard denes the maximum line length as a function of data rate (in Mbps). This implies that the user must choose between the line length of the network
and its maximum data transmission rate.
The isolated interface has been used in previous congurations (e.g. NM232D) to increase the available line length as isolated data lines are much less susceptible to
ground currents and variations in local supplies. The feature of isolation in a LON environment is intended to be used primarily to improve noise susceptibility, therefore,
unless the line length improvements can be reliably demonstrated by the user, the EIA-485 recommendations on maximum cable length are assumed to apply.
The complete hardware implementation for the LONWORKS EIA-485 network is relatively straight forward (see gure 2). There is a minimum of components required,
only 1 interface part and one resistor, and the complete LONTALK transmission protocols are supported. The isolation barrier of 1000Vrms offers improved noise immunity
compared to a non-isolated system and eliminates node-to-node supply voltage mismatch and possible ground current loops.
TECHNICAL NOTES
ISOLATION VOLTAGE
‘Hi Pot Test’, ‘Flash Tested’, ‘Withstand Voltage’, ‘Proof Voltage’, ‘Dielectric Withstand Voltage’ & ‘Isolation Test Voltage’ are all terms that relate to the same thing, a test voltage,
applied for a specied time, across a component designed to provide electrical isolation, to verify the integrity of that isolation.
Murata Power Solutions NM485SLC series of DC/DC converters are all 100% production tested at their stated isolation voltage. This is 1000Vrms for 1 second.
A question commonly asked is, “What is the continuous voltage that can be applied across the part in normal operation?”
For a part holding no specic agency approvals, such as the NM485SLC series, both input and output should normally be maintained within SELV limits i.e. less than 42.4V peak,
or 60VDC. The isolation test voltage represents a measure of immunity to transient voltages and the part should never be used as an element of a safety isolation system. The part
could be expected to function correctly with several hundred volts offset applied continuously across the isolation barrier; but then the circuitry on both sides of the barrier must
be regarded as operating at an unsafe voltage and further isolation/insulation systems must form a barrier between these circuits and any user-accessible circuitry according to
safety standard requirements.
REPEATED HIGH-VOLTAGE ISOLATION TESTING
It is well known that repeated high-voltage isolation testing of a barrier component can actually degrade isolation capability, to a lesser or greater degree depending on materials,
construction and environment. The NM485SLC series has toroidal isolation transformers, with no additional insulation between primary and secondary windings of enameled wire.
While parts can be expected to withstand several times the stated test voltage, the isolation capability does depend on the wire insulation. Any material, including this enamel
(typically polyurethane) is susceptible to eventual chemical degradation when subject to very high applied voltages thus implying that the number of tests should be strictly limited.
We therefore strongly advise against repeated high voltage isolation testing, but if it is absolutely required, that the voltage be reduced by 20% from specied test voltage. This
consideration equally applies to agency recognized parts rated for better than functional isolation where the wire enamel insulation is always supplemented by a further insulation
system of physical spacing or barriers.
Figure 3
Figure 2
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