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_______________general description the max3320 combines a microprocessor (?) super- visory circuit with an rs-232 transceiver. the power-on reset performs a single function: it asserts a reset signal whenever the v cc supply voltage declines below a pre- set threshold, staying asserted for at least 100ms after v cc rises above the reset threshold. the max3320 has an active-low reset output, which is guaranteed to be in the correct state for v cc down to 1v. the reset compara- tor is designed to ignore fast transients on v cc . reset thresholds suitable for operation with a variety of supply voltages are available. the max3320 transceivers have a proprietary low- dropout transmitter output stage, enabling true rs-232 performance with a dual charge pump powered from a +3v to +5.5v supply. the device requires only four small 0.1? external charge-pump capacitors, and is guaranteed to run at data rates of up to 250kbps. it comes in the space-saving 20-pin ssop package. ________________________applications palmtop computers portable/battery-powered equipment hand-held equipment peripherals printers ____________________________features ? precise monitoring of 5v and 3.3v power- supply voltages: ?100ms (min) power-on reset pulse width ?power-supply transient immunity ?guaranteed reset valid to v cc = 1v ? 4? supply current achieved with autoshutdown plus ? receivers always active ? power-on reset always active ? 4? low-power shutdown ? 250kbps guaranteed data rate max3320a/b/l/t 3v to 5.5v, up to 250kbps true rs-232 transceiver with 4? autoshutdown plus and power-on reset ________________________________________________________________ maxim integrated products 1 20 19 18 17 16 15 14 13 1 2 3 4 5 6 7 8 c1+ v cc c1- gnd v- c2- c2+ v+ top view t1out t2out r1in r2in r2out r1out t2in t1in 12 11 9 10 forceon forceoff reset invalid maxxxx ssop max3320 __________________pin configuration 19-1253; rev 0; 8/97 part* max3320 _ cap max3320_eap -40? to +85? 0? to +70? temp. range pin-package 20 ssop 20 ssop ______________ordering information * this part offers a choice of reset threshold voltage. from the table below, select the suffix corresponding to the desired threshold and insert it into the blank to complete the part number. autoshutdown plus is a trademark of maxim integrated products. suffix a b reset threshold (v) 4.25 2.85 l 4.63 t 3.08 typical operating circuit appears at end of data sheet. for free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. for small orders, phone 408-737-7600 ext. 3468.
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = 3v to 5.5v, c1?4 = 0.1 f (tested at 3.3v 10%), c1 = 0.047 f, c2?4 = 0.33 f (tested at 5v 10%), t a = t min to t max , unless otherwise noted. typical values are at t a = +25 c.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v cc ............................................................................. -0.3v to 6v v+ (note 1) ................................................................. -0.3v to 7v v- (note 1) ................................................................... 0.3v to -7v v+ + | v- | (note 1) ................................................................... 13v input voltages t_in, forceoff , forceon ................................ -0.3v to 6v r_in ................................................................................. 25v output voltages t_out .......................................................................... 13.2v r_out, invalid , reset ....................... -0.3v to (v cc + 0.3v) short-circuit duration t_out .................................................................... continuous continuous power dissipation (t a = +70 c) ssop (derate 8.00mw/ c above +70 c) .................... 640mw operating temperature ranges max3320_cap ................................................... 0 c to +70 c max3320_eap ................................................ -40 c to +85 c storage temperature range ............................. -65 c to +160 c lead temperature (soldering, 10sec) ............................. +300 c v -0.3 0.3 figure 3 receiver input threshold to invalid output low -2.7 figure 3, negative threshold v 2.7 figure 3, positive threshold receiver input threshold to invalid output high k w 3 5 7 t a = +25 c input resistance v 0.3 input hysteresis 1.8 2.4 v cc = 5v v 1.5 2.4 v cc = 3.3v input threshold high 0.8 1.5 v cc = 5v v 0.6 1.2 v cc = 3.3v input threshold low v -25 25 input voltage range a 4.0 10 forceoff = gnd, t a = +25 c shutdown supply current ma 0.45 1.0 no load, v cc = 3.3v or 5v, t a = +25 c power-supply current v v cc - v cc - 0.6 0.1 i out = -1ma output voltage high v 0.4 i out = 1.6ma output voltage low mv 250 t_in, forceon, forceoff input hysteresis a 0.01 1.0 t_in, forceon, forceoff input leakage current a 4.0 10 all r_in unconnected, forceon = gnd, forceoff = v cc , all t_in = v cc or gnd, t a = +25 c autoshutdown plus supply current v 0.8 t_in, forceon, forceoff input logic threshold low v 2.0 input logic threshold high units min typ max conditions parameter t_in, forceon, forceoff 2.4 v 0.4 i out = 1.6ma invalid output voltage low note 1: v+ and v- can have a magnitude of +7v (max), but their absolute difference cannot exceed +13v. v cc = 3.3v v cc = 5v dc characteristics logic inputs and receiver outputs receiver inputs invalid output
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset _______________________________________________________________________________________ 3 sec 15 30 60 figure 3 receiver or transmitter edge to shutdown s 25 figure 5 receiver or transmitter edge to transmitters enabled 90 s figure 3 receiver positive or negative threshold to invalid low s 0.1 figure 3 receiver positive or negative threshold to invalid high units min typ max conditions parameter electrical characteristics (continued) (v cc = 3v to 5.5v, c1?4 = 0.1 f (tested at 3.3v 10%), c1 = 0.047 f, c2?4 = 0.33 f (tested at 5v 10%), t a = t min to t max , unless otherwise noted. typical values are at t a = +25 c.) v 5.0 5.4 all transmitter outputs loaded with 3k w to ground output voltage swing w 300 10m v cc = v+ = v- = gnd, v t_out = 2v output resistance ma 35 60 t_out = gnd, t_in = v cc or gnd output short-circuit current a 25 v t_out = 12v, v cc = 0 to 5.5v, transmitters disabled output leakage current v 1.0 5.5 max3320_c reset operating voltage range 1.2 5.5 max3320_e v 4.00 4.25 4.50 max3320a reset threshold 2.70 2.85 3.00 max3320b 4.50 4.63 4.75 max3320l 3.00 3.08 3.15 max3320t v 0.3 i sink = 1.2ma, v cc = reset threshold, max3320b/t reset output voltage 0.4 i sink = 3.2ma, v cc = reset threshold, max3320a/l 0.3 i sink = 50 a, v cc > 1v, max3320_c 0.4 i sink = 100 a, v cc > 1.2v, max3320_e v v cc - 0.6 i out = -1ma invalid output voltage high autoshutdown plus (forceon = gnd, forceoff = v cc ) transmitter outputs reset output
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset 4 _______________________________________________________________________________________ -7.5 v t_out- v t_out+ -2.5 -5.0 2.5 0 5.0 7.5 0 2000 1000 3000 4000 5000 transmitter output voltage vs. load capacitance max3320 toc01 load capacitance (pf) output voltage (v) one transmitter at 250kbps one transmitter at 15.6kbps load = 3k w + c l 0 2 8 6 4 10 12 0 2000 1000 3000 4000 5000 slew rate vs. load capacitance max3320 toc02 load capacitance (pf) slew rate (v/us) one transmitter at 250kbps one transmitter at 15.6kbps load = 3k w + c l negative slew positive slew 0 250kbps 120kbps 20kbps 10 5 30 20 25 15 40 35 45 0 2000 1000 3000 4000 5000 supply current vs. load capacitance when transmitting data max3320 toc03 load capacitance (pf) supply current (ma) one transmitter at full data rate indicated one transmitter at 1/16 data rate indicated timing characteristics (v cc = 3v to 5.5v, c1?4 = 0.1 f, c1?4 = 0.1 f (for 3.3v 10%), c1 = 0.047 f, c2?4 = 0.33 f (tested at 5v 10%), t a = t min to t max , unless otherwise noted. typical values are at t a = +25 c.) kbps 250 r l = 3k w , c l = 1000pf, one transmitter switching maximum data rate ns 100 | t phl - t plh | transmitter skew 0.3 s 0.3 r_in to r_out, c l = 150pf receiver propagation delay units min typ max conditions parameter t plh t phl ns 200 | t phl - t plh | receiver skew c l = 150pf to 1000pf v/ s 6 30 v cc = 3.3v, r l = 3k w to 7k w , measured from +3v to -3v or -3v to +3v, t a = +25 c transition-region slew rate ms 100 280 v cc = reset threshold reset active timeout period s 40 100mv overdrive from reset threshold v cc to reset delay c l = 150pf to 2500pf 4 30 __________________________________________ t ypical operating characteristics (v cc = 3.3v, 250kbps data rate, c1?4 = 0.1 f, all transmitters loaded with 3k w . typical values are at t a = +25 c, unless otherwise noted.)
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset _______________________________________________________________________________________ 5 ______________________________________________________________ pin description 300 0 10 100 1000 maximum transient duration vs. reset comparator overdrive 50 max3320toc05 reset comparator overdrive (mv) maximum transient duration (?) 100 200 150 250 not in shutdown mode shutdown mode c bypass = 0.1 m f 0.960 0.970 1.010 1.000 0.990 0.980 1.030 1.020 1.040 -40 0 -20 20 40 80 60 normalized power-up reset delay vs. temperature max3320 toc06 temperature (?) power-up reset delay ____________________________ t ypical operating characteristics (continued) (v cc = 3.3v, 250kbps data rate, c1?4 = 0.1 f, all transmitters loaded with 3k w . typical values are at t a = +25 c, unless otherwise noted.) 20 c1+ positive terminal of voltage-doubler charge-pump capacitor 19 v cc +3v to +5.5v supply voltage 18 c1- negative terminal of voltage-doubler charge-pump capacitor name function 1 v+ 5.5v generated by the charge pump 2 c2+ positive terminal of inverting charge-pump capacitor pin 3 c2- negative terminal of inverting charge-pump capacitor 4 v- -5.5v generated by the charge pump 10 reset reset output. reset remains low while v cc is below the reset threshold, and for 280ms (max) after v cc rises above the reset threshold. 9 invalid output of the valid signal detector. asserts when no valid rs-232 levels are present on any of the receiver inputs for 90 s. 7, 8 r_out ttl/cmos receiver outputs (r1out and r2out) 5, 6 t_in ttl/cmos transmitter inputs (t1in and t2in) 17 gnd ground 15, 16 t_out rs-232 transmitter outputs (t2out and t1out) 13, 14 r_in rs-232 receiver inputs (r2in and r1in) 12 forceon force-on input. drive forceon high to override autoshutdown plus, keeping transmitters on ( forceoff must be high) (table 1). 11 forceoff force-off input. drive forceoff low to shut down transmitters and on-board power supply. this overrides autoshutdown plus and forceon (table 1).
max3320a/b/l/t 6 _______________________________________________________________________________________ ______________ detailed description dual charge-pump voltage converter the max3320 s internal power supply consists of a reg - ulated dual charge pump that provides output voltages of +5.5v (doubling charge pump) and -5.5v (inverting charge pump) while v cc remains in the 3v to 5.5v range. the charge pumps operate in discontinuous mode; they are enabled if the output voltages are less than 5.5v, and disabled if output voltages exceed 5.5v. each charge pump requires a flying capacitor (c1, c2) and a reservoir capacitor (c3, c4) to generate the v+ and v- supplies. rs-232 transmitters the transmitters are inverting level translators that con - vert cmos-logic levels to 5v eia/tia-232 levels. the max3320 transmitters guarantee a 250kbps data rate with worst-case loads of 3k w in parallel with 1000pf, providing compatibility with pc-to-pc communication software (such as laplink). transmitters can be par - alleled to drive multiple receivers. figure 1 shows a complete system connection. when forceoff is driven to ground, the transmitter s outputs become high impedance. when the autoshutdown plus circuitry senses that all receiver and transmitter inputs are inactive for more than 30sec, the transmitters turn off and the outputs go into a high- impedance state, but the receivers remain active. when the power is off or the max3320 is shut down, outputs may be driven up to 12v. the transmitter inputs do not have pull-up resistors. connect unused inputs to gnd or v cc . laplink is a trademark of traveling software. rs-232 receivers the receivers convert rs-232 signals to cmos-logic out - put levels. all receivers have inverting outputs and are active in shutdown forceoff (table 1). autoshutdown plus mode maxim? autoshutdown plus feature, which operates when forceoff is high and forceon is low, achieves a 4 a supply current. when the max3320 senses no valid signal levels on all receiver and transmitter inputs for 30sec, the on-board power supply and drivers shut off, max3320 i/o chip with uart cpu rs-232 power- management unit or keyboard controller forceoff forceon invalid t1 t2 r1 r2 figure 1. interface under control of pmu table 1. max3320 output control truth table forceoff 0 high-z t_out active r_out 1 active active normal operation (forced on) x 1 1 active active normal operation (autoshutdown plus) <30sec* 0 1 high-z active shutdown (autoshutdown plus) >30sec* 0 forceon shutdown (forced off) x x operation status autoshutdown plus* x = don? care * time since last receiver or transmitter input activity 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset _______________________________________________________________________________________ 7 reducing supply current to 4 a. this occurs if the rs-232 cable is disconnected or the connected peripheral trans - mitters turn off. the system turns on again when a valid transition occurs at any rs-232 receiver or transmitter input. as a result, the system saves power without changes to the existing bios or operating system. the invalid output is high when the receivers are active. since invalid indicates the receiver inputs?condition, it can be used in any mode (figure 2). tables 1 and 2 and figure 2 summarize the max3320 s operating modes. forceon and forceoff override the automatic circuitry and force the transceiver into its normal operating state or into its low-power standby state. when neither control is asserted, the ic enters autoshutdown plus mode and selects between these states automatically, based on the last receiver or transmitter input edge received. when shut down, the device? charge pumps turn off, v+ decays to v cc , v- decays to ground, and the trans - mitter outputs turn off (high impedance). the time required to exit shutdown is typically 25 s (figure 3a). software-controlled shutdown if direct software control is desired, use invalid to indi - cate dtr or ring indicator signal. connect forceoff and forceon together to bypass the autoshutdown plus feature so the line acts like a shdn input. power-on reset in addition to issuing a reset to the microprocessor ( p) during power-up, power-down, and brownout condi - tions, the max3320 is relatively immune to short- duration, negative-going v cc transitions (glitches). typically, a v cc transient that goes 100mv below the reset threshold and lasts 20 s or less does not cause a reset pulse (see typical operating characteristics ). additional bypass capacitance mounted as close as possible to the v cc pin provides additional transient immunity. table 2. invalid truth table max3320 +0.3v -0.3v invalid r_in invalid asserted if both receiver inputs are between +0.3v and -0.3v for at least 90 m s. 90? timer r figure 2a. invalid functional diagram, invalid low +2.7v -2.7v r_in invalid deasserted if either receiver input has been between +2.7v and -2.7v for less than 90 m s. invalid 90? timer r figure 2b. invalid functional diagram, invalid high autoshdn r_in t_in r s 30sec timer edge detect edge detect forceoff forceon figure 2c. autoshutdown plus logic powerdown* autoshdn forceoff forceon * powerdown is only an internal signal. it controls the operational status of the transmitters and the power supplies. figure 2d. power-down logic yes rs-232 signal present at receiver input no l h invalid output
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset 8 _______________________________________________________________________________________ __________applications infor mation ensuring a valid reset output down to v cc = 0v when v cc falls below 1v, reset no longer sinks cur - rent: it becomes an open circuit. therefore, high- impedance cmos logic inputs connected to reset can drift to undefined voltages. this presents no prob - lem in most applications, since most ps and other cir - cuitry is inoperative with v cc below 1v. however, in applications where reset must be valid down to 0v, add a pull-down resistor to ground, holding reset low (figure 4). r1? value is not critical; 100k w is large enough not to load reset, and small enough to pull it to ground. capacitor selection the capacitor type used for c1?4 is not critical for proper operation; use either polarized or nonpolarized capacitors. the charge pump requires 0.1 f capaci - tors for 3.3v operation. for other supply voltages, refer to table 3 for required capacitor values. do not use val - ues smaller than those listed in table 3. increasing the capacitor values (e.g., by a factor of 2) reduces ripple on the transmitter outputs and slightly reduces power consumption. c2, c3, and c4 can be increased without changing c1's value. however, do not increase c1 without also increasing the values of c2, c3, c4, and c bypass , to maintain the proper ratios (c1 to the other capacitors). receiver input levels -2.7v -0.3v 2.7v 0.3v 0v indeterminate invalid high invalid low invalid high indeterminate figure 3b. receiver positive/negative thresholds for invalid figure 3a. autoshutdown plus and invalid timing diagram v cc 0 v+ v- v cc 0 invalid output * all receiver/transmitter inputs inactive ** any one receiver/transmitter input becomes active forceon = gnd, forceoff = v cc transmitter inputs voltage receiver inputs voltage transmitter outputs voltage t autoshdn invalid region * ** t wu t wu i nvl t autoshdn
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset _______________________________________________________________________________________ 9 when using the minimum required capacitor values, make sure the capacitor value does not degrade excessively with temperatures outside the 0 c to +70 c range. if in doubt, use capacitors with a larger nominal value. the capacitor's equivalent series resistance (esr), which usually rises at low temperatures, influ - ences the amount of ripple on v+ and v-. transmitter outputs when exiting shutdown figure 5 shows two transmitter outputs when exiting shutdown mode. as they become active, the two trans - mitter outputs go to opposite rs-232 levels (one trans - mitter input is high; the other is low). each transmitter is loaded with 3k w in parallel with 2500pf. the transmitter outputs display no ringing or undesirable transients as they exit shutdown. note that the transmitters are enabled only when the magnitude of v- exceeds approximately 3v. high data rates the max3320 maintains the rs-232 5v minimum transmitter output voltage even at high data rates. figure 6 shows a transmitter loop-back test circuit. figure 7 shows a loop-back test result at 120kbps, and figure 8 shows the same test at 250kbps. for figure 7, both transmitters were driven simultaneously at 120kbps into rs-232 loads in parallel with 1000pf. for figure 8, a single transmitter was driven at 250kbps, and both transmitters were loaded with an rs-232 receiver in parallel with 1000pf. interconnection with 3v and 5v logic the max3320 can directly interface with various 5v logic families, including act and hct cmos. see table 4 for more information on possible combinations of interconnections. v cc = 3.3v c1 - c4 = 0.1 m f 5 m s/div 2v/div 2v/div t2out t1out forceon = forceoff figure 5. transmitter outputs when exiting shutdown or powering up max3320 5k r_ in r_ out c2- c2+ c1- c1+ v- v+ v cc c4 c3* c1 c2 v cc forceoff t_ out t_ in gnd v cc *c3 can be returned to v cc or gnd. forceon 1000pf figure 6. loop-back test circuit max3320 gnd 100k v cc v cc reset figure 4. ensuring reset valid to v cc = 0v 0.1 0.47 3 to 5.5 0.047 0.33 4.5 to 5.5 c1 ( f) 0.1 c2, c3, c4, c bypass ( f) 0.1 v cc (v) 3 to 3.6 table 3. required minimum capacitance values
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset 10 ______________________________________________________________________________________ ___________________ chip infor mation transistor count: 1577 3.3 system power-supply voltage (v) 5 compatible with all ttl and cmos families compatible with all cmos families compatibility 3.3 v cc supply voltage (v) 5 5 compatible with act and hct cmos, and with ac, hc, or cd4000 cmos 3.3 table 4. logic-family compatibility with various supply voltages t1out r1in r1out t1in 5v 0v -5v 0v 5v 5v 0v 2 m s/div v cc = 3.3v c1 - c4 = 0.1 m f c load = 1000pf figure 7. loop-back test result at 120kbps t1out r1in r1out t1in 5v 0v -5v 0v 5v 5v 0v 2 m s/div v cc = 3.3v c1 - c4 = 0.1 m f c load = 1000pf figure 8. loop-back test result at 250kbps
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset ______________________________________________________________________________________ 11 t1 t2 t1in c2- c2+ c1- c1+ v+ v- t1out t2out t2in forceon r1 r1out r2out c1 0.1 m f autoshutdown plus r2 gnd r2in 5k 5k r1in v cc v cc v cc *c3 may be returned to either v cc or gnd. rs-232 inputs rs-232 outputs c2 0.1 m f max3320 c3* 0.1 m f c4 0.1 m f 0.1 m f +3.3v m p system forceoff reset reset input invalid ___________________________________________________ t ypical operating cir cuit
max3320a/b/l/t 3v to 5.5v , up to 250kbps t r ue rs-232 t ransceiver with 4 a autoshutdown plus and power -on reset ________________________________________________________ package infor mation ssop.eps maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 12 ____________________ maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 1997 maxim integrated products printed usa is a registered trademark of maxim integrated products.

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