DS1487 DS1487 low power rs-485 ? unit load multipoint transceiver literature number: snls132
DS1487 low power rs-485 1 4 unit load multipoint transceiver general description the DS1487 is a low-power transceiver for rs-485 and rs-422 communication. the device contains one driver and one receiver. the drivers slew rate allows for operation up to 2.0 mbps (see applications information section). the trans- ceiver presents 1 4 unit loading to the rs-485 bus allowing up to 128 nodes to be connected together without the use of re- peaters. the transceiver draws 200 a of supply current when un- loaded or fully loaded with the driver disabled and operates from a single +5v supply. the driver is short-circuit current limited and is protected against excessive power dissipation by thermal shutdown circuitry that places the driver outputs into tri-state ? (high impedance state) under fault conditions. the driver guarantees a minimum of 1.5v differential output voltage with maximum loading across the common mode range (v od3 ). the receiver has a failsafe feature that guarantees a logic-high output if the input is open circuit. the DS1487 is available in surface mount and dip pack- ages. features n meets tia/eia rs-485 multipoint standard n allows up to 128 transceivers on the bus ( 1 4 u.l.) n guaranteed full load output voltage (v od3 ) n low quiescent current: 200 a typ n ?7v to +12v common-mode input voltage range n tri-state outputs on driver and receiver n ac performance: e driver transition time: 25 ns typ e driver propagation delay: 40 ns typ e driver skew: 1 ns typ e receiver propagation delay: 200 ns typ e receiver skew: 20 ns typ n half-duplex flow through pinout n operates from a single 5v supply n current-limiting and thermal shutdown for driver overload protection n pin and functional compatible with max1487 connection and logic diagram order number temp. range package/ ### DS1487n 0c to +70c dip/n08e DS1487m 0c to +70c sop/m08a truth table driver section re (note 1) de di a b xhhhl xhl lh xlxzz receiver section re (note 1) de a-b ro ll 3 +0.2v h ll ?0.2v l hx x z l l open (note 1) h x = indeterminate z = tri-state note 1: non terminated, open input only tri-state ? is a registered trademark of national semiconductor corporation. dip and soic ds012920-1 *note: non terminated, open input only july 1998 DS1487 low power rs-485 1 4 unit load multipoint transceiver ? 2000 national semiconductor corporation ds012920 www.national.com
absolute maximum ratings (note 2) if military/aerospace specified devices are required, please contact the national semiconductor sales office/ distributors for availability and specifications. supply voltage (v cc ) +12v enable input voltage (re (note 1), de) ?0.5v to (v cc + 0.5v) driver input voltage (di) ?0.5v to (v cc + 0.5v) driver output voltage (a, b) ?14v to +14v receiver input voltage (a, b) ?14v to +14v receiver output voltage (ro) ?0.5v to (v cc + 0.5v) maximum package power dissipation @ +25c m package 1.19w n package 0.74w derate m package 9.5 mw/c above +25c derate n package 6.0 mw/c above +25c maximum package power dissipation @ +70c m package 0.76w n package 0.47w storage temperature range ?65c to +150c lead temperature range (soldering, 4 sec.) +260c esd (hbm) 3 2kv recommended operating conditions min typ max units supply voltage (v cc ) +4.75 +5.0 +5.25 v operating free air temperature (t a ) DS1487 0 +25 +70 c bus common mode voltage ?7 +12 v electrical characteristics over supply voltage and operating temperature ranges, unless otherwise specified (notes 3, 4) symbol parameter conditions pin min typ max units v od1 differential driver output voltage (no load) a, b 1.5 5 v v od2 differential driver output voltage r l =50 w , (rs422), figure 1 2 2.8 v with load r l =27 w , (rs485), figure 1 1.5 2.3 5 v d v od change in magnitude of output r l =27 w or 50 w (note 5) 0.2 |v| differential voltage v od3 differential driver output voltage e r1 = 54 w , r2 = 375 w 1.5 2.0 5 v full load with max v cm v test = ?7v to +12v, figure 2 v oc driver common-mode output voltage r l =27 w or 50 w , figure 1 03v d v oc change in magnitude of common-mode output voltage r l =27 w or 50 w , figure 1 (note 5) 0.2 |v| v ih input high voltage di, de, 2.0 v v il input low voltage re (note 1) 0.8 v i in1 input current v in =0vorv cc 2a i in2 input current (note 6) v in = +12v a, b 0 190 250 a de = 0v, v cc = 0v or 5.25v v in = ?7v 0 ?100 ?200 a v th receiver differential threshold voltage ?7v v cm +12v ?0.2 0.2 v d v th receiver input hysteresis v cm =0v 70 mv v oh receiver output high voltage i o = ?4 ma, v id = 0.2v ro 3.5 v v ol receiver output low voltage i o = 4 ma, v id = ?0.2v 0.5 v i ozr tri-state output current at receiver 0.4v v o 2.4v 1a r in receiver input resistance ?7v v in +12v a, b 48 68 k w i cc no-load supply current (note 7) de = v cc , re (note 1) = 0v or v cc v cc 200 500 a de = 0v, re (note 1) = 0v or v cc 200 500 a i osd1 driver short circuit current, v o = high ?7v v o +12v a, b 250 ma i osd2 driver short circuit current, v o = low ?7v v o +12v ?250 ma i osr receiver short circuit current v o = gnd ro 7 85 ma DS1487 www.national.com 2
switching characteristics over supply voltage and operating temperature ranges, unless otherwise specified (notes 4, 8, 9) symbol parameter conditions min typ max units t plhd driver differential propagation delay e low to high r l =54 w ,c l = 100 pf 10 40 80 ns t phld driver differential propagation delay e high to low 10 39 80 ns t skew differential skew |t phld ?t plhd |0110ns t r driver rise time 32550 ns t f driver fall time 32550 ns t zh driver enable to output high c l = 100 pf 50 200 ns t zl driver enable to output low c l = 100 pf 65 200 ns t lz driver disable from output low c l = 15 pf 80 200 ns t hz driver disable from output high c l = 15 pf 80 200 ns t plhd receiver differential propagation delay e low to high c l = 15 pf (ro) 30 190 400 ns t phld receiver differential propagation delay e high to low 30 210 400 ns t skew differential skew |t phld ?t plhd | 0 20 50 ns t zh receiver enable to output high c l = 15 pf 45 150 ns t zl receiver enable to output low 40 150 ns t lz receiver disable from output low 50 150 ns t hz receiver disable from output high 55 150 ns f max maximum data rate (note 10) 2.0 mbps note 2: aabsolute maximum ratingso are those values beyond which the safety of the device cannot be guaranteed. they are not meant to imply that the devices should be operated at these limits. the table of aelectrical characteristicso specifies conditions of device operation. note 3: current into device pins is defined as positive. current out of device pins is defined as negative. all voltages are referenced to ground except v od1/2/3 and v id . note 4: all typicals are given for: v cc = +5.0v, t a = +25c. note 5: d |v od | and d |v oc | are changes in magnitude of v od and v oc respectively, that occur when the input changes state. note 6: i in2 includes the receiver input current and driver tri-state leakage current. note 7: supply current specification is valid for loaded transmitters when de = 0v or enabled (de = h) with no load. note 8: f = 1 mhz, t r and t f 6 ns, z o =50 w . note 9: c l includes jig and probe capacitance. note 10: f max is the guaranteed data rate for 50 ft of twisted pair cable. f max may be conservatively determined from the ratio of driver transition time (t r ) to the data rate unit interval (1/f max ). using a 10% ratio yields f max = (0.1)/50 ns = 2.0 mb/s. higher data rates may be supported by allowing larger ratios. parameter measurement information ds012920-2 figure 1. v od ds012920-3 figure 2. v od3 ds012920-4 figure 3. DS1487 www.national.com 3
parameter measurement information (continued) ds012920-5 figure 4. ds012920-6 figure 5. ds012920-7 figure 6. ds012920-8 figure 7. ds012920-9 figure 8. ds012920-10 *note: non terminated, open input only figure 9. ds012920-11 figure 10. ds012920-12 *note: non terminated, open input only figure 11. DS1487 www.national.com 4
parameter measurement information (continued) pin descriptions pin # i/o name function 1 o ro receiver output: if a > b by 200 mv, ro will be high; if a < b by 200 mv, ro will be low. ro will be high also if the inputs (a and b) are open (non-terminated). 2 i re (note 1) receiver output enable: ro is enabled when re (note 1) is low; ro is in tri-state when re (note 1) is high. 3 i de driver output enable: the driver outputs (a and b) are enabled when de is high; they are in tri-state when de is low. pins a and b also function as the receiver input pins (see below). 4 i di driver input: a low on di forces a low and b high while a high on di forces a high and b low when the driver is enabled. 5 na gnd ground 6 i/o a non-inverting driver output and receiver input pin. driver output levels conform to rs-485 signaling levels. 7 i/o b inverting driver output and receiver input pin. driver output levels conform to rs-485 signaling levels. 8na v cc power supply: 4.75v v cc 5.25v applications information the DS1487 is a low power transceiver designed for use in rs-485 multipoint applications. the DS1487 can transmit data up to 2.0 mbps based on a ratio of driver transition time to the unit interval (bit time) of 10%. this maximum data rate may be further limited by the interconnecting media. the DS1487 provides a 1 4 unit load to the rs-485 bus across the common mode range of ?7v to +12v. this allows up to 128 transceivers ( 1 4 unit load) to be connected to the bus. the DS1487 also guarantees the driver's output differential volt- age into a worst case load that models standard termination loads and 32 unit loads (=128 DS1487's) referenced to the maximum common mode voltage extremes. with a minimum of 1.5v swing into this load, a 1.3v differential noise margin is supported along with the standard common mode rejec- tion range of the receivers. ds012920-13 *note: non terminated, open input only figure 12. ds012920-14 *note: non terminated, open input only figure 13. DS1487 www.national.com 5
applications information (continued) due to the multipoint nature of the bus, contention between drivers may occur. this will not cause damage to the drivers since they feature short-circuit protection and also thermal shutdown protection. thermal shutdown senses die tem- perature and puts the driver outputs into tri-state if a fault condition occurs that causes excessive power dissipation which can elevate the junction temperature to +150c. a typical multipoint application is shown in the following fig- ure. note that termination is typically required but is only lo- cated at the two ends of the cable (not on every node). com- monly pull up and pull down resistors may be required at one end of the bus to provide a failsafe bias. these resistors pro- vide a bias to the line when all drivers are in tri-state. see national application note 847 for a complete discussion of failsafe biasing of differention buses. ds012920-16 DS1487 www.national.com 6
physical dimensions inches (millimeters) unless otherwise noted order number DS1487n ns package number n08e DS1487 www.national.com 7
notes life support policy national's products are not authorized for use as critical components in life support devices or systems without the express written approval of the president and general counsel of national semiconductor corporation. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. a critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. national semiconductor corporation americas tel: 1-800-272-9959 fax: 1-800-737-7018 email: support@nsc.com national semiconductor europe fax: +49 (0) 180-530 85 86 email: europe.support@nsc.com deutsch tel: +49 (0) 69 9508 6208 english tel: +44 (0) 870 24 0 2171 fran?ais tel: +33 (0) 1 41 91 87 90 national semiconductor asia pacific customer response group tel: 65-2544466 fax: 65-2504466 email: ap.support@nsc.com national semiconductor japan ltd. tel: 81-3-5639-7560 email: nsj.crc@jksmtp.nsc.com fax: 81-3-5639-7507 www.national.com DS1487 low power rs-485 1 4 unit load multipoint transceiver national does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and national reserves the righ t at any time without notice to change said circuitry and specifications.
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