mc1488 rs232c quad line driver ? march 2000 n current limited output 10ma typ. n power-off source impedance 300 w min. n simple slew rate control with external capacitor n flexible operating supply range n inputs are ttl and m p compatible description the mc1488 is a monolithic quad line driver designed to interface data terminal equipment with data communications equipment in conformance with the specifications of eia standard no. rs232c. p dip14 (plastic package) order codes : mc1488p (plastic dip) MC1488D (so14) d so14 (plastic micropackage) logic diagram pin connections (top view) 1/9
electrical characteristics v s = 9 10%v, v e e = C 9 10%v ,t amb = 0 to 75 o c, unless otherwise specified symbol parameter test conditions min. typ. max. unit fig. i il input current low logic statev il = 0v 1 1.6 ma 1 i ih input current high logic statev ih = 5v 10 m a1 v oh output voltage high logic stater l = 3k w v il = 0.8v, v s = 9v, v ee = C9v v il = 0.8v, v s = 13.2v, v ee = C13.2v 6 9 7 10.5 v 2 2 v ol output voltage low logic state v ih = 1.9v, v ee = C9v, v s = 9v v ih = 1.9v, v ee = C13.2v, v s = 13.2v -6 -9 -7 -10.5 v 2 2 i os + * positive output short-circuit current 6 10 12 ma 3 i os C * negative output short-circuit current -6 -10 -12 ma 3 r o output resistance v s = v ee = 0v ol = 2v 300 w 4 i s positive supply current (r i = ) v ih = 1.9v v s = 9v v il = 0.8v v s = 9v v ih = 1.9v v s = 12v v il = 0.8v v s = 12v v ih = 1.9v v s = 15v v il = 0.8v v s = 15v 15 4.5 19 5.5 20 6 25 7 34 12 ma 5 i ee negative supply current (r l = ) v ih = 1.9v v s = -9v v il = 0.8v v s = -9v v ih = 1.9v v s = -12v v il = 0.8v v s = -12v v ih = 1.9v v s = -15v v il = 0.8v v s = -15v -13 -18 -17 -15 -23 -15 -34 -2.5 ma m a ma m a ma ma 5 p c power consumption v s = 9v v ee = -9v v s = 12v v ee = -12v 333 567 mw absolute maximum ratings symbol parameter test conditions unit v s power supply voltage 15 v v ee power supply voltage C15 v v ir input voltage range C15 v ir 7v v o output signal voltage 15 v t amb operating ambient temperature 0 to 75 o c t stg storage temperature range C65 to 150 o c thermal data symbol parameter plastic dip14 ceramic dip14 so14 r th j-amb thermal resistance junction-ambientmax. 200 o c/w 165 o c/w 165 o c/w switching characteristics v s = 9 1v, v e e = C 9 1%v ,t amb = 25 o c symbol parameter test conditions min. typ. max. unit fig. t phl propagation delay time z i = 3k w and 15pf 275 350 ns 6 t thl fall time z i = 3k w and 15pf 45 75 ns 6 t phl propagation delay time z i = 3k w and 15pf 110 175 ns 6 t thl rise time z i = 3k w and 15pf 55 100 ns 6 * maximum package power dissipation may be exceeded if all outputs are shorted simultaneously. mc1488 2/9
test circuits figure 1 : input current figure 3 : output short-circuit current figure 5 : power supply currents figure 2 : output voltage figure 4 : output resistance (power off) figure 6 : switching response mc1488 3/9
figure 7 : transfer characteristics versus figure 8 : short-circuit output current versus temperature figure 9 : output slew-rate load capacitance figure 10 : output voltage and current limiting characteristics figure 11 : maximum operating temperature versus power supply voltage mc1488 4/9
typical application : rs232c data transmission the electronic industries association (eia) has released the rs232c specification detailing the requirements for the interface between data processing equipment. this standard specifies not only the number and type of interface leads, but also the voltage levels to be used. the mc1488 quad driver and its companion circuit, the mc1489 quad receiver, provide a complete interface system between dtl or ttl logic levels and the rs232c defined levels. the rs232c requirements as applied to drivers are discussed herein. the required driver voltages are defined as between 5 and 15 v in magnitude and are positive for a logic "0" and negative for a logic "1". these voltages are so defined when the drivers are terminated with a 3000 to 7000 w resistor. the mc1488 meets this voltage requirement by converting a dtl/ttl logic level into rs232c levels with one stage of inversion. the rs232c specification further requires that during transitions, the driver output slew rate must not exceed 30 v per m s. the inherent slew rate of the mc1488 is much too fast for this requirement. the current limited output of the device can be used to control this slew rate by connecting a capacitor to each driver output. the required capacitor can be easily determined by using the relationship c = i os x d t/ d v from which figure 12 is derived. accordingly, a 330 pf capacitor on each output will guarantee a worst case slew rate of 30 v per m s. the interface driver is also required to withstand an accidental short to any other conductor in an interconnecting cable. the worst possible signal on any conductor would be another driver using a plus or minus 15 v, 500 ma source. the mc1488 is designed to indefinitely withstand such a short to all four outputs in a package as long as the power-supply voltages are greater than 9.0 v (i.e., vs 3 9.0 v ; v ee - 9.0 v). in some power-supply designs, a loss of system power causes a low impedance on the power-supply outputs. when this occurs, a low impedance to ground would exist at the power inputs to the mc1488 effectively shorting the 300 w output resistor to ground. if all four outputs were then shorted to plus or minus 15 v, the power dissipation in these resistors would be excessive. therefore, if the system is designed to permit low impedances to ground at the power-suppies of the drivers, a diode should be placed in each power-supply lead to prevent over-heating in this fault condition. these two diodes, as shown in figure 13, could be used to decouple all the driver packages in a system. (these same diodes will allow the mc1488 to withstand momentary shorts to the 15 v limits specified in the earlier application information mc1488 5/9
standard rs232b). the addition of the diodes also permits the mc1488 to withstand faults with power-supplies of less than the 9.0 v stated above. the maximum short-circuit current allowable under fault conditions is more than guaranteed by the previously mentioned 10 ma output current limiting. the mc1488 is an extremely versatile line driver with a miriad of possible applications. several features of the drivers enhance this versatility : 1. output current limiting - this enables the circuit designer to define the ouptut voltage levels independent of power-supplies and can be accomplished by diode clamping of the output pins. 2. power-supply range - as can be seen from the schematic drawing of the drivers, the positive and negative driving elements of the device are essentially independent and do not require matching power-supplies. in fact, the positive supply can very from a minimum seven volts (required for driving the negative pulldown section) to the maximum specified 15 v. the negative supply can vary from approximately - 2.5 v to the minimum specified - 15 v. the mc1488 will drive the ouptut to within 2 v of the positive or negative supplies as long as the current output limits are not exceeded. the combination of the current-limiting and supply-voltage features allow a wide combination of possible outputs within the same quad package. figure 12 : slew rate versus capacitance for i sc = 10ma figure 13 : power supply protection to meet power-off fault conditions mc1488 6/9
dim. mm inch min. typ. max. min. typ. max. a1 0.51 0.020 b 1.39 1.65 0.055 0.065 b0.5 0.020 b1 0.25 0.010 d200.787 e8.5 0.335 e2.54 0.100 e3 15.24 0.600 f7.10.280 i5.10.201 l3.3 0.130 z 1.27 2.54 0.050 0.100 p001a plastic dip-14 mechanical data mc1488 7/9
dim. mm inch min. typ. max. min. typ. max. a1.750.068 a1 0.1 0.2 0.003 0.007 a2 1.65 0.064 b 0.35 0.46 0.013 0.018 b1 0.19 0.25 0.007 0.010 c0.5 0.019 c1 45 (typ.) d 8.55 8.75 0.336 0.344 e 5.8 6.2 0.228 0.244 e1.27 0.050 e3 7.62 0.300 f 3.8 4.0 0.149 0.157 g 4.6 5.3 0.181 0.208 l 0.5 1.27 0.019 0.050 m0.680.026 s 8 (max.) p013g so-14 mechanical data mc1488 8/9
information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the co nsequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specification mentioned in this pu blication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectron ics products are not authorized for use as critical components in life support devices or systems without express written approval of stmicr oelectronics. the st logo is a registered trademark of stmicroelectronics ? 2000 stmicroelectronics C printed in italy C all rights reserved stmicroelectronics group of companies australia - brazil - china - finland - france - germany - hong kong - india - italy - japan - malaysia - malta - morocco singapore - spain - sweden - switzerland - united kingdom - u.s.a. http://www.st.com . mc1488 9/9
|
