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参数资料
| 型号： | IL3422E |
| 厂商： | NVE Corp/Isolation Products |
| 文件页数： | 2/18页 |
| 文件大小： | 0K |
| 描述： | TXRX ISO BUS 20MBPS RS422 16SOIC |
| 产品培训模块： | IsoLoop® Isolator |
| 产品目录绘图： | IL3122, 3222, 3422 Circuit |
| 特色产品： | Wide-Body SOIC-16 Isolators |
| 标准包装： | 50 |
| 系列： | IsoLoop® |
| 类型： | 收发器，隔离式 |
| 驱动器/接收器数： | 1/1 |
| 规程： | RS422 |
| 电源电压： | 3 V ~ 5.5 V，4.5 V ~ 5.5 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.295"，7.50mm 宽） |
| 供应商设备封装： | 16-SOIC |
| 包装： | 管件 |
| 产品目录页面： | 2771 (CN2011-ZH PDF) |
| 其它名称： | 390-1100-5 |
IL3485/IL3422
10
NVE Corporation
11409 Valley View Road, Eden Prairie, MN 55344-3617
Phone: (952) 829-9217
Fax: (952) 829-9189
www.IsoLoop.com
NVE Corporation
Typical Coil Connections
R
RE
A
B
V
DD2
V
COIL2
V
COIL1
V
DD1
DE
D
R1
16pF ±50%
R2
R3
A
B
Z
R
RE
Y
V
COIL2
V
DD2
V
COIL1
V
DD1
DE
D
R1
R2
R3
16pF ±50%
VDD1 = VDD2 = 5 V
R1, R2, R3 = 820
VDD1 = 3.3 V
R1, R2 = 510 ; R3 = 820
VDD1 = VDD2 = 5 V
R1, R2, R3 = 820
VDD1 = 3.3 V
R1, R2 = 510 ; R3 = 820
Fail-Safe Operation
“Fail-safe operation” is defined here as the forcing of a logic high state on the “R” output in response to an open-circuit condition
between the “A” and “B” lines of the bus, or when no drivers are active on the bus.
Proper biasing can ensure fail-safe operation, that is a known state when there are no active drivers on the bus. IL3485 and IL3422
Isolated Transceivers include internal pull-up and pull-down resistors of approximately 30 k in the receiver section (RFS-INT; see
figure on following page). These internal resistors are designed to ensure failsafe operation but only if there are no termination
resistors. The entire VDD will appear between inputs “A” and “B” if there is no loading and no termination resistors, and there will
be more than the required 200 mV with up to four RS-485/RS-422 worst-case Unit Loads of 12 k. Many designs operating below
1 Mbps or less than 1,000 feet are unterminated. Termination resistors may not be necessary for very low data rates and very short
cable runs because reflections have time to settle before data sampling, which occurs at the middle of the bit interval.
In busses with low-impedance termination resistors, however, the differential voltage across the conductor pair will be close to
zero with no active drivers. In this case the state of the bus is indeterminate, and the idle bus will be susceptible to noise. For
example, with 120 termination resistors (RT) on each end of the cable, and four Unit Loads (12 k each), without external fail-
safe biasing resistors the internal pull-up and pull-down resistors will produce a voltage between inputs “A” and “B” of only about
5 mV. This is not nearly enough to ensure a known state. External fail-safe biasing resistors (RFS-EXT) at one end of the bus can
ensure fail-safe operation with a terminated bus. Resistors should be selected so that under worst-case power supply and resistor
tolerances there is at least 200 mV across the conductor pair with no active drivers to meet the input sensitivity specification of the
RS-422 and RS-485 standards.
Using the same value for pull-up and pull-down biasing resistors maintains balance for positive- and negative going transitions.
Lower-value resistors increase inactive noise immunity at the expense of quiescent power consumption. Note that each Unit Load
on the bus adds a worst-case loading of 12 k across the conductor pair, and 32 Unit Loads add 375 worst-case loading. The
more loads on the bus, the lower the required values of the biasing resistors.
In the example with two 120 termination resistors and four Unit Loads, 560 external biasing resistors provide more than
200 mV between “A” and “B” with adequate margin for power supply variations and resistor tolerances. This ensures a known
state when there are no active drivers. Other illustrative examples are shown in the following table:
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