NM485DC series isolated dual eia-485 driver and receiver kii_NM485DC.a05 page 1 of 6 www.murata-ps.com www.murata-ps.com/support for full details go to www.murata-ps.com/rohs $ electrical characteristics parameter test conditions min. typ. max. units supply voltage, v cc 4.75 5.0 5.25 v high level input voltage, v ih d x enable and d inputs 2.8 v low level input voltage, v il 0.8 v common mode output voltage, v oc driver -7.0 12 v high level output current i oh -60 ma low level output current, i ol 60 ma common mode input voltage, v ic receiver 12 v differential input voltage, v id 12 v high level output current, i oh -5.0 ma low level output current, i ol 25 ma each receiver electrical characteristics parameter test conditions min. typ. max. units high threshold differential input, v th v o =2.7v, i o =-0.4ma 0.2 v low threshold differential input, v tl v o =0.5v, i o =16ma -0.2 v input hysteresis, v t 50 mv high level output voltage, v oh v id =200mv, i oh =-5.0ma 2.7 v low level output voltage, v ol v id =200mv, i ol =25ma 0.8 v line input current, i i other input at 0v, v i =12v 1.0 ma other input at 0v, v i =-12v -0.8 ma short circuit output current, i os -15 ma input resistance, r i 12 k receiver switching characteristics parameter test conditions min. typ. max. units propagation delay time l to h, t plh v id =-1.5v to 1.5v, c l =15pf 70 155 ns propagation delay time h to l, t phl 72 135 ns receiver function table differential inputs a-b rx out v id 0.2v high level -0.2vNM485DC is an electrically isolated dual differential driver and receiver designed for bal- anced mulipoint bus transmission at rates up to 1.25mbits per second. the device provides two receive channels and two driver channels. the two driver channels have an active high enable. no external components are needed and a single 5v input supply powers all functions either side of the isolation boundary. the driver outputs provide limiting for positive and negative currents and thermal shutdown protection from line fault condi- tions on the transmission bus line. the receiver outputs will always be high if the receiver inputs are open. the isolation voltage between input and output is 1000vrms, the devices are supplied in a low pro?le 24 pin dil plastic package. ual n electrical characteristics not recommended ot recomme for new designs
NM485DC series isolated dual eia-485 driver and receiver kii_NM485DC.a05 page 2 of 6 www.murata-ps.com/support each driver electrical characteristics parameter test conditions min. typ. max. units high level output voltage, v oh i oh =-33ma 3.7 v low level output voltage, v ol i oh =33ma 1.1 v differential output voltage, v od1 i o =0 1.5 6.0 v differential output voltage, v od2 r l =100 2.0 v r l =54 1.5 5.0 v change in magnitude of differential output voltage, v od r l =54 or 100 0.2 v common mode output voltage, v oc -1.0 3.0 v change in magnitude of common mode output voltage, v oc 0.2 v output current power off, i o v cc =0, v o =-7.0v to 12v 100 a high level input current, i ih v ih =4.0v 2.0 20 a low level input current, i il v il =0.8v -15 ma short circuit output current, i os v o =-7.0v 1 -250 ma v o =12v 1 250 ma driver switching characteristics parameter test conditions min. typ. max. units differential output delay time, t dd r l =54, cl=50pf 20 25 ns output disable time from high level, t phz r l =110, cl=50pf 90 120 ns output disable time from low level, t plz r l =110, cl=50pf 30 45 ns propagation delay time l to h, t plh r l =27, cl=50pf 70 145 ns propagation delay time h to l, t phl 70 145 ns differential output transition time, t td r l =54, cl=50pf 150 300 ns output enable time to high level, t pzh r l =110, cl=50pf 80 120 ns output enable time to low level, t pzl r l =110, cl=50pf 40 60 ns driver function table dx in d x enable dx y output dx z output high level high level high level low level low level high level low level high level irrelevant low level high impedance high impedance temperature characteristics parameter min. typ. max. units operating free-air temperature range 060oc storage temperature range -40 125 oc 1. duration of short circuit should not exceed 1 second.
NM485DC series isolated dual eia-485 driver and receiver kii_NM485DC.a05 page 3 of 6 www.murata-ps.com/support application notes the eia-485 standard is an upgrade version of the eia rs-422 standard. the use of balanced data transmission lines in distribut ing data to several systems components and peripherals over relatively long lines, requires the use of multiple driver/receiver combinations on a single twisted pair line. this is referred to as a party-line (see ?gure 1). the NM485DC is an isolated interface device providing eia-485 compatibility. a single supply provides all necessary power for t he device, either side of the isolation bound- ary. the isolation feature allows the logic and differential grounds to be isolated from each other, eliminating ground loop cu rrent and inherently long noise paths. the maximum number of drivers and receivers that may be placed on a single communication bus depends upon their loading charact eristics, relative to the de?nition of a unit load (u.l.), transmission speed does not affect the unit load capability. as the NM485DC complies with the eia-485 stand ard a maximum of 32 unit loads per line is recommended. a unit load usually consists of a driver-receiver pair, but not the line termination resistors. with only a 5v supply connected, the NM485DC receiver and differential outputs give levels greater than +2.7v and 1.5v respect ively. this known output state may be used as a reference for use in environments with considerable levels of noise. an unused driver should be disabled by grounding its enable pin to reduce power dissipation. figure 2 illustrates the way one receiver and one driver of the NM485DC may be connected to implement an isolated eia-485 inter face with a typical uart and processor bus. figure 3 demonstrates how the NM485DC may be used as a transceiver. this is possible by using the driver enable to determi ne the data direction. for example, the device could receive when the driver enable is low and transmit when it is high. precise circuitry will depend on the application and in particular the use of the control lines shown will need to be altered t o suit the situation. for instance the maximum sychronous baud rate of the 8251a is 64kbps, whereas the NM485DC had a maximum baud rate of 1.25mbps. implementing an isolated lonworks ( ? ) network using the NM485DC the echleon lonworks (local operating network) network is designed to be used in industrial applications in which other eletrical equipment is operated. often the lon (r) will be the method of controlling machinery or sensing machine activity. the environment is therefore likely to be electrically noisy and to reduce the possibility of data corruption, an isolated network communications system is a preferred method of data transfer. the eia-485 standard provides a method of achieving multi- point (multi-drop) data transmission over balanced twisted pair transmission lines. the standard is a differential scheme offering a large degree of common mode immunity compared to single ended schemes. the isolated differential method offers the highest common mode and line noise immunity for wire based systems. the NM485DC is a fully isolated eia-485 standard dual driver and receiver, which requires only a single 5v supply. the device offers full data direction programming and can hence be con?gured as a transceiver. the NM485DC can be operated at transmitting or receiving data rates of up to 1.25mbps, hence is fully compatible with the lontalk ( ? ) transmission rate standards. con?guring the nm485d as a transceiver the nm485d is con?gured as a transceiver simply by con- necting the inverting r1 b receive to the inverting d1 z drive and the non-inverting r1 a receive to the non-inverting d1 y drive, similarly r2 b to d2 z and r2 a to d2 y for the second transceiver (see ?gure 3), in this way the nm485d is con?gured as a dual transceiver. the data direction is determined by the driver en- able pins (d x enable), the transceiver acting as a transmitter when the enable pin is high and a receiver when the enable pin is low. if only a single transceiver is required it is recommended that the second transceiver driver is disabled, this reduces the power consumption to around 0.6w. the second driver is disabled by taking the driver enable pin low, this should be via a pull-down resistor (recommend value is 1k). 3 5 3 5 3 f d f j w f s 3 f d f j w f s % s j w f s % s j w f s $ p n n p o * t p m b u f e ( s p v o e - j o f % " 5 " 5 & |