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_______________general description the max3238 true rs-232 transceiver achieves a 1? supply current with maxim? revolutionary autoshutdown plus feature. when the device does not sense a valid signal transition on either the receiver or transmitter inputs within 30sec, the on-board power supply and drivers shut down. this occurs if the rs-232 cable is disconnected or if the transmitters of the con- nected peripheral are inactive. the system turns on again when a valid transition is applied to any rs-232 receiver or transmitter input, saving power without changes to the existing bios or operating system. the max3238 5-driver/3-receiver complete serial port is a 3v-powered eia/tia-232 and v.28/v.24 communica- tions interface intended for notebook or subnotebook computer applications. a proprietary, high-efficiency, dual charge-pump power supply and a low-dropout transmitter combine to deliver true rs-232 performance from a single +3.0v to +5.5v supply. a guaranteed data rate of 250kbps provides compatibility with popu- lar software for communicating with personal comput- ers. the max3238 requires only 0.1? capacitors in 3.3v operation. it is ideal for 3.3v-only systems, mixed 3.3v and 5.0v systems, or 5v-only systems that require true rs-232 performance. receiver r1 has an extra, always-active output (in addi- tion to its standard output), which allows external devices, such as a modem, to be monitored without for- ward biasing the protection diodes in circuitry that may have v cc completely removed. the max3238 is available in a space-saving ssop package. ________________________applications notebook, subnotebook, and palmtop computers high-speed modems battery-powered equipment hand-held equipment peripherals printers autoshutdown plus i s a trademark of maxim integrated products. * p ____________________________features 1a supply current achieved with autoshutdown plus guaranteed data rate: 250kbps 1a low-power shutdown receivers active in autoshutdown plus mode flow-through pinout meets eia/tia-232 specifications down to 3.0v guaranteed 6v/s slew rate max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus ________________________________________________________________ maxim integrated products 1 28 27 26 25 24 23 22 21 20 19 18 17 16 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 c1+ v+ v cc c1- t1in t2in invalid t3in r1out r2out t4in r3out t5in r1outb forceoff forceon t5out r3in t4out r2in r1in t3out t2out t1out v- c2- gnd c2+ ssop top view max3238 __________________pin configuration 19-1144; rev 1; 10/02 part max3238cai max3238eai -40? to +85? 0? to +70? temp range pin-package 28 ssop 28 ssop ______________ordering information typical operating circuit appears at end of data sheet. for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com.
max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +3.0v to +5.5v; c1?4 = 0.1? (tested at 3.3v ?%), c1?4 = 0.22? (tested at 3.3v ?0%), c1 = 0.047? and c2?4 = 0.33? (tested at 5.0v ?0%); t a = t min to t max ; unless otherwise noted. typical values are at t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications 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 .................................................................................?5v output voltages t_out...........................................................................?3.2v r_out, invalid ....................................-0.3v to (v cc + 0.3v) short-circuit duration t_out (one at a time) ............................................continuous continuous power dissipation (t a = +70?) ssop (derate 9.52mw/? above +70?) ....................762mw operating temperature ranges max3238cai ......................................................0? to +70? max3238eai....................................................-40? to +85? storage temperature range ............................-65? to +160? lead temperature (soldering, 10s) ................................+300? forceoff = gnd, t a = +25? v cc = 3.3v or 5.0v, t a = +25?, receivers idle, transmitters idle, forceon = gnd, forceoff = v cc i out = -1.0ma i out = 1.6ma receivers disabled t_in, forceon, forceoff forceon = forceoff = v cc , no load t_in, forceon, forceoff v cc = 3.3v conditions ? 1.0 10 supply current, shutdown ? 1.0 10 supply current, autoshutdown plus v v cc -v cc - 0.6 0.1 output voltage high v 0.4 output voltage low ? ?.05 ?0 output leakage current ? ?.01 ?.0 input leakage current ma 0.5 2.0 supply current, autoshutdown plus disabled v 0.8 input logic threshold low v 2.0 input logic threshold high units min typ max parameter note 1: v+ and v- can have a maximum magnitude of +7v, but their absolute difference can not exceed +13v. v cc = 5.0v 2.4 v -25 25 input voltage range v cc = 3.3v 0.6 1.2 v cc = 5.0v v 0.8 1.5 input threshold low v cc = 3.3v 1.5 2.4 v cc = 5.0v v 1.8 2.4 input threshold high v 0.3 input hysteresis t a = +25? k? 357 input resistance dc characteristics logic inputs and receiver outputs receiver inputs
max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = +3.0v to +5.5v; c1?4 = 0.1? (tested at 3.3v ?%), c1?4 = 0.22? (tested at 3.3v ?0%), c1 = 0.047? and c2?4 = 0.33? (tested at 5.0v ?0%); t a = t min to t max ; unless otherwise noted. typical values are at t a = +25?.) figure 4a figure 7a figure 4b (note 2) v cc = 5v, figure 4b (note 2) v cc = 5v, figure 4b i out = 1.6ma i out = -1.0ma v cc = 5v, figure 4b conditions v -0.3 0.3 receiver input threshold to invalid output low v 2.7 receiver input threshold to invalid output high sec 15 30 60 receiver or transmitter edge to shutdown (t autoshdn ) ? 25 receiver or transmitter edge to transmitters enabled (t wu ) ? 50 receiver positive or negative threshold to invalid low (t invl ) v 0.4 invalid output voltage low v v cc - 0.6 invalid output voltage high ? 0.1 receiver positive or negative threshold to invalid high (t invh ) units min typ max parameter positive threshold negative threshold -2.7 output voltage swing all transmitter outputs loaded with 3k? to ground ?.0 ?.4 v output resistance v cc = v+ = v- = gnd, t out = 2v 300 10m ? v cc 3.6v ?5 ?0 output leakage current v out = ?2v, v cc = 0v to 5.5v, transmitters disabled ?5 ? | t phl - t plh | 43 0 t phl r_in to r_out, c l = 150pf t plh c l = 150pf to 1000pf r l = 3k?, c l = 1000pf, one transmitter switching c l = 150pf to 2500pf 0.15 v cc = 3.3v, t a = +25?, r l = 3? to 7k?, measured from +3v to -3v or -3v to +3v normal operation normal operation | t phl - t plh | ? 0.15 receiver propagation delay kbps 250 maximum data rate v/? 63 0 transition-region slew rate ns 200 receiver output enable time ns 200 receiver output disable time ns 100 transmitter skew ns 50 receiver skew timing characteristics output short-circuit current v cc > 3.6v ?0 ?00 autoshutdown (forceon = gnd, forceoff = v cc ) transmitter outputs note 2: a transmitter/receiver edge is defined as a transition through the transmitter/receiver input logic thresholds. ma
______________________________________________________________pin description 7.5 -5.0 -7.5 0 1000 3000 5000 transmitter output voltage vs. load capacitance -2.5 5.0 max3238 toc-01 load capacitance (pf) transmitter output voltage (v) 2000 4000 2.5 0 v out + v out for data rates up to 250kbps 1 transmitter 250kbps 4 transmitters 15.6kbps loaded 3k? + c l 14 4 2 0 0 1000 3000 5000 slew rate vs. load capacitance 6 12 max3238-02 slew rate (v/s) load capacitance (pf) 2000 4000 10 8 +slew slew 1 transmitter 250kbps 4 transmitters 15.6kbps loaded 3k? + c l 70 20 10 0 0 1000 3000 5000 supply current vs. load capacitance when transmitting data 30 60 max3238 toc-03 supply current (ma) load capacitance (pf) 2000 4000 50 40 250kbps 120kbps 20kbps __________________________________________typical operating characteristics (v cc = +3.3v, 250kbps data rate, 0.1? capacitors, all transmitters loaded with 3k ?, t a = +25?, unless otherwise noted.) max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus 4 _______________________________________________________________________________________ positive terminal of voltage-doubler charge-pump capacitor c1+ 28 +5.5v generated by the charge pump v+ 27 +3.0v to +5.5v supply voltage v cc 26 name function 1 c2+ positive terminal of inverting charge-pump capacitor 2 gnd ground pin 3 c2- negative terminal of inverting charge-pump capacitor 4 v- -5.5v generated by the charge pump 14 forceoff force-off input. drive low to shut down transmitters, receivers (except r1outb), and on- board supply. this overrides autoshutdown plus and forceon (table 1). 13 forceon force-off input. drive high to override autoshutdown plus, keeping transmitters and receivers on (forceoff must be high) (table 1). 8, 9, 11 r_in rs-232 receiver inputs (r1in?3in) 5, 6, 7, 10, 12 t_out rs-232 transmitter outputs (t1out?5out) 25 c1- negative terminal of voltage-doubler charge-pump capacitor 18, 20, 21 r_out ttl/cmos receiver outputs (r3out?1out) 17, 19, 22, 23, 24 t_in ttl/cmos transmitter inputs (t5in?1in) 16 r1outb noninverting complementary receiver output. always active. 15 invalid output of the valid signal detector. a logic ??indicates if a valid rs-232 level is present on receiver inputs.
max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus _______________________________________________________________________________________ 5 _______________detailed description dual charge-pump voltage converter the max3238? 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), regardless of the input voltage (v cc ) over the 3.0v to 5.5v range. the charge pumps operate in a discontinuous mode: if the output voltages are less than 5.5v, the charge pumps are enabled; if the output voltages exceed 5.5v, the charge pumps are disabled. 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 5.0v eia/tia-232 levels. the max3238 transmitters guarantee a 250kbps data rate with worst-case loads of 3k ? 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. laplink is a trademark of traveling software. when forceoff is driven to ground, the transmitters and receivers are disabled and the outputs go high impedance, except for r1outb. when the auto- shutdown plus circuitry senses that all receiver and transmitter inputs are inactive for more than 30sec, the transmitters are disabled and the outputs go into a high-impedance state, but the receivers remain active. when the power is off, the max3238 permits the out- puts to be driven up to ?2v. the transmitter inputs do not have pull-up resistors. connect unused inputs to gnd or v cc . rs-232 receivers the receivers convert rs-232 signals to cmos-logic output levels. all receivers have inverting three-state outputs and are inactive in shutdown ( forceoff) (table 1). the max3238 also features an extra, always- active noninverting output, r1outb. this extra output monitors receiver activity while the other receivers are high impedance, allowing ring indicator to be moni- tored without forward biasing other devices connected to the receiver outputs. this is ideal for systems where v cc is set to 0v in shutdown to accommodate peripher- als, such as uarts (figure 2). table 1. output control truth table forceon f f o o r r c c e e o o f f f f autoshutdown plus* operation status t_out r_out r1outb x 0 x shutdown (forced off) high-z high-z active 1 1 x normal operation (forced on) active active active 0 1 <30sec* normal operation (autoshutdown plus) active active active 0 1 >30sec* shutdown (autoshutdown plus) high-z active active x = don? care * time since last receiver or transmitter input transition.
max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus 6 _______________________________________________________________________________________ autoshutdown plus mode 1? supply current is achieved with maxim? autoshutdown plus feature, which operates when forceoff is high and forceon is low. when the max3238 senses no valid signal transitions on all receiver and transmitter inputs for 30sec, the on-board power supply and drivers are shut off, reducing supply current to 1?. this occurs if the rs-232 cable is dis- connected or if the connected peripheral transmitters are turned off. the system turns on again when a valid transition is applied to any rs-232 receiver or transmit- ter 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 3). max3238 i/o chip with uart cpu rs-232 power management unit or keyboard controller forceoff forceon invalid t1 t2 t3 t4 t5 r1 r2 r3 figure 1. interface under control of pmu max3238 t1out r1outb tx 5k? uart v cc t1in three-stated logic transition detector r1in protection diode r1out forceoff = gnd v cc to p rx previous rs-232 tx uart shdn = gnd v cc v cc gnd rx 5k? (a) older rs-232: powered-down uart draws current from active receiver output in shutdown. (b) new max3238: in shutdown, r1outb is used to monitor external devices and r1out is three stated, eliminating a current path through the uart's protection diode. gnd protection diode i i figure 2. the max3238 detects rs-232 activity when the uart and interface are shut down.
max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus _______________________________________________________________________________________ 7 tables 1 and 2 and figure 3 summarize the max3238? 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 are disabled (high impedance). the time required to exit shutdown is typically 25s (figure 4b). software-controlled shutdown if direct software control is desired, use invalid to indicate dtr or ring indicator signal. tie forceoff and forceon together to bypass the autoshutdown feature so the line acts like a shdn input. __________applications information capacitor selection the capacitor type used for c1?4 is not critical for proper operation; polarized or nonpolarized capacitors can be used. the charge pump requires 0.1? capaci- tors for 3.3v operation. for other supply voltages, see 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? 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). table 2. i i n n v v a a l l i i d d truth table +0.3v -0.3v invalid r_in invalid asserted if all receiver inputs are between +0.3v and -0.3v for at least 30s. 30s timer r +2.7v -2.7v invalid r_in invalid deasserted if any receiver input has been between +2.7v and -2.7v for less than 30s. 30s timer r autoshdn r_in t_in r s 30sec timer edge detect edge detect forceoff forceon figure 3a. invalid functional diagram, invalid low figure 3b. invalid functional diagram, invalid high figure 3c. 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 3d. power-down logic l no h yes i i n n v v a a l l i i d d output rs-232 signal present at any receiver input
when using the minimum required capacitor values, make sure the capacitor value does not degrade excessively with temperature. if in doubt, use capaci- tors with a larger nominal value. the capacitor? equiv- alent series resistance (esr), which usually rises at low temperatures, influences the amount of ripple on v+ and v-. max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus 8 _______________________________________________________________________________________ table 3. required minimum capacitance values receiver input levels -2.7v -0.3v +2.7v +0.3v 0v indeterminate invalid high invalid low invalid high indeterminate figure 4a. receiver positive/negative thresholds for invalid v cc 0 v+ v- v cc 0 invalid output * all receivers/transmitters inactive ** any one receiver/transmitter 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 figure 4b. autoshutdown plus and invalid timing diagram 1 0.22 3.0 to 5.5 0.33 0.047 4.5 to 5.5 c2, c3, c4, c bypass (f) 0.22 0.1 0.1 3.15 to 3.6 0.22 3.0 to 3.6 c1 (f) v cc (v)
power-supply decoupling in applications that are sensitive to power-supply noise, decouple v cc to ground with a capacitor of the same value as capacitors c2, c3, and c4. connect the bypass capacitor as close to the ic as possible. transmitter outputs when exiting shutdown figure 5 shows two transmitter outputs when exiting shutdown mode. as they become active, the outputs are shown going to opposite rs-232 levels (one trans- mitter input is high, the other is low). each transmitter is loaded with 3k? in parallel with 2500pf. the transmitter outputs display no ringing or undesirable transients as they come out of shutdown. note that the transmitters are enabled only when the magnitude of v- exceeds approximately 3v. high data rates the max3238 maintains the rs-232 ?.0v minimum transmitter output voltage even at high data rates. figure 6 shows a transmitter loopback test circuit. figure 7 shows a loopback test result at 120kbps, and figure 8 shows the same test at 250kbps. for figure 7, all 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 all transmitters were loaded with an rs-232 receiver in parallel with 1000pf. interconnection with 3v and 5v logic the max3238 can directly interface with various 5v- logic families, including act and hct cmos. see table 4 for more information on possible combinations of interconnections. max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus _______________________________________________________________________________________ 9 v cc = 3.3v c1 - c4 = 0.1f 5s/div 2v/div 2v/div t2out t1out forceon = forceoff figure 5. transmitter outputs when exiting shutdown or powering up table 4. logic family compatibility with various supply voltages system power- supply voltage (v) v cc supply voltage (v) compatibility 3.3 3.3 compatible with all cmos families. 5 5 compatible with all ttl and cmos families. 5 3.3 compatible with act and hct cmos, and with ac, hc, or cd4000 cmos. max3238 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. loopback test circuit
max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus 10 ______________________________________________________________________________________ v cc = 3.3v c1 - c4 = 0.1f c load = 1000pf 2s/div t1in t1out r1out 5v 0v 0v 0v +5v 5v -5v figure 8. loopback test result at 250kbps v cc = 3.3v c1 - c4 = 0.1f c load = 1000pf 2s/div t1in t1out r1out 0v 0v 0v 5v +5v 5v -5v figure 7. loopback test result at 120kbps ___________________chip information transistor count: 1404
max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus ______________________________________________________________________________________ 11 max3238 rs-232 outputs logic inputs rs-232 inputs logic outputs *c3 may be returned to either v cc or gnd. forceoff invalid autoshutdown plus forceon t1in t1out t2in t2out t3in t3out t4in t4out t5in 5 6 7 10 12t5out 15 24 23 22 19 c1+ v cc v+ c1- c2+ v- c2- 27 * 26 4 28 0.1f 0.1f 0.1f 0.1f 25 1 3 17 r1outb16 r1out 8r1in 21 r2out 9r2in 20 r3out 11 5k? 5k? 5k? gnd 2 r3in 18 14 13 t1 t2 t3 t4 t5 r1 r2 r3 0.1f __________typical operating circuit
maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit 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 2002 maxim integrated products printed usa is a registered trademark of maxim integrated products. max3238 +3.0v to +5.5v, 1a, up to 250kbps, true rs-232 transceiver with autoshutdown plus l dim a a1 b c d e e h l dim d d d d d min 0.068 0.002 0.010 0.004 0.205 0.301 0.025 0? min 0.239 0.239 0.278 0.317 0.397 max 0.078 0.008 0.015 0.008 0.209 0.311 0.037 8? max 0.249 0.249 0.289 0.328 0.407 min 1.73 0.05 0.25 0.09 5.20 7.65 0.63 0? min 6.07 6.07 7.07 8.07 10.07 max 1.99 0.21 0.38 0.20 5.38 7.90 0.95 8? pins 14 16 20 24 28 max 6.33 6.33 7.33 8.33 10.33 inches inches millimeters millimeters ssop shrink small-outline package h e d a a1 c b 0.65 bsc 0.0256 bsc 21-0056a e see variations package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .)

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