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general description the max3387e 3v powered tia/eia-232 and v.28/v.24is a communications interface with low power require- ments, high data-rate capabilities, and enhanced elec- trostatic discharge (esd) protection. the max3387e has three receivers and three transmitters. all rs-232 inputs and outputs are protected to ?5kv using the iec 1000-4-2 air-gap discharge method, ?kv usingthe iec 1000-4-2 contact discharge method, and ?5kv using the human body model.a proprietary low-dropout transmitter output stage enables true rs-232 performance from a +3.0v to +5.5v supply with a dual charge pump. the charge pump requires only four small 0.1? capacitors for operation from a +3.3v supply. the max3387e is capa- ble of running at data rates up to 250kbps while main- taining rs-232 compliant output levels. the max3387e has a unique v l pin that allows interop- eration in mixed-logic voltage systems. both input andoutput logic levels are pin programmable through the v l pin. the max3387e is available in a space-saving tssop package. applications subnotebook/palmtop computerspdas and pda cradles cell phone data cables battery-powered equipment hand-held equipment peripherals features ? v l pin for compatibility with mixed-voltage systems ? ?5kv esd protection on rx inputs and tx outputs ? low 300? supply current ? guaranteed 250kbps data rate ? 1? autoshutdown plus with receivers active ? meets tia/eia-232 specifications down to 3.0v max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones _______________________________________________________________ maxim integrated products 1 c1 0.1 f c2 0.1 f max3387e r2out 13 r1out 14 r2in 17 gnd 22 rs-232outputs ttl/cmos inputs t2in 8 t1in 7 c2- 5 c2+ 4 c1- 3 c1+ 1 r1in 18 t2out 20 t1out 21 v- 6 v+ 2 v cc v l c40.1 f 23 15 c bypass +3.3v t3in 10 t3out 19 rs-232inputs ttl/cmos outputs c30.1 f 5k 5k v l v l r3out 12 r3in 16 5k v l forceoff 24 invalid 9 11 forceon typical operating circuit 19-1561; rev 3; 6/10 ordering information autoshutdown plus is a trademark of maxim integrated products, inc. part MAX3387ECUG+ max3387eeug+ temp. range 0? to +70? -40? to +85? pin-package 24 tssop 24 tssop for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. + denotes a lead(pb)-free/rohs-compliant package. downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones 2 _______________________________________________________________________________________ absolute maximum ratings dc electrical characteristics(v cc = v l = +3.0v to +5.5v; c1?4 = 0.1?, tested at +3.3v ?0%; c1 = 0.047?, c2?4 = 0.33?, tested at +5.0v ?0%; t a = t min to t max , unless otherwise noted. typical values are at v cc = v l = +3.3v, 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. note 1: v+ and v- can have maximum magnitudes of 7v, but their absolute difference cannot exceed 13v. v cc to gnd ..............................................................-0.3v to +6v v l to gnd...................................................-0.3v to (v cc + 0.3v) v+ to gnd ................................................................-0.3v to +7v v- to gnd .................................................................+0.3v to -7v v+ + ? v- ? (note 1) .............................................................. +13v input voltages t_in, forceon, forceoff to gnd ..................-0.3v to +6v r_in to gnd .....................................................................?5v output voltages t_out to gnd...............................................................?3.2v r_out........................................................-0.3v to (v l + 0.3v) short-circuit duration t_out to gnd........................continuous continuous power dissipation (t a = +70?) 24-pin tssop (derate 12.2mw/? above +70?) ........976mw operating temperature ranges MAX3387ECUG ...................................................0? to +70? max3387eeug ................................................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? soldering temperature (reflow) .......................................+260? i out = 1.6ma all r_in idle, forceon = gnd, forceoff = v cc , all t_in idle t_in, forceon, forceoff t_in, forceon,forceoff forceoff = forceon = v cc , no load conditions v 0.4 output voltage low ? ?.01 ? input leakage current v 0.5 transmitter input hysteresis v 0.9 input logic threshold high 1.4 2.0 ? 1.0 10 supply current, autoshutdownplus 2.4 v 0.8 0.3 1 ma supply current units min typ max symbol parameter v l = +5.0v v l = +3.3v v l = +2.5v v l = +1.8v i out = -1ma v v l - v l - 0.6 0.1 output voltage high v l = +3.3v or +5.0v t_in, forceon,forceoff 0.6 input logic threshold low v l = +2.5v v -25 +25 input voltage range t a = +25? v 0.8 1.5 input threshold low v l = +5.0v v l = +3.3v 0.6 1.2 t a = +25? v 1.8 2.4 input threshold high v l = +5.0v v l = +3.3v 1.5 2.4 dc characteristics (v cc = +3.3v or +5v, t a = +25?) logic inputs receiver outputs receiver inputs downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones _______________________________________________________________________________________ 3 dc electrical characteristics (continued)(v cc = v l = +3.0v to +5.5v; c1?4 = 0.1?, tested at +3.3v ?0%; c1 = 0.047?, c2?4 = 0.33?, tested at +5.0v ?0%; t a = t min to t max , unless otherwise noted. typical values are at v cc = v l = +3.3v, t a = +25?.) autoshutdown plus (forceon = gnd, forceoff = v cc ) esd protection transmitter outputs -2.7 negative threshold figure 3a positive threshold receiver or transmitter edge totransmitters shutdown t autoshdn 15 30 60 s receiver positive or negativethreshold to invalid low t invl 30 v cc = +5v, figure 3b receiver or transmitter edge totransmitters enabled t wu 100 ? v cc = +5v, figure 3b ? v cc = +5v, figure 3b receiver positive or negativethreshold to invalid high t invh 1 ? invalid output voltage low 0.4 v cc = +5v, figure 3b invalid output voltage high v l - 0.6 v i out = -1.6ma v i out = -1.0ma receiver input threshold toinvalid output low -0.3 0.3 v receiver input threshold toinvalid output high 2.7 v figure 3a r_in, t_out esd protection ? kv iec 1000-4-2 contact discharge method parameter symbol min typ max units input hysteresis 0.5 v input resistance 357 k output voltage swing ? ?.4 v output resistance 300 10m output short-circuit current ?0 ma output leakage current ?5 ? ?5 ?5 conditions t a = +25? all transmitter outputs loaded with 3k to ground v cc = v+ = v- = 0v, transmitter output = ?v v t _ out = 0v v t _ out = ?2v, transmitters disabled; v cc = 0v or +3.0v to +5.5v human body model iec 1000-4-2 air-gap discharge method transmitter outputs esd protection autoshutdown plus (forceon = gnd, forceoff = v cc ) downloaded from: http:///
-7.5 -5.0 -2.5 0 2.5 5.0 7.5 0 1000 2000 3000 4000 5000 transmitter output voltage vs. load capacitance max3387e-01 load capacitance (pf) output voltage (v) data rate = 250kbpsload = 3k in parallel with c l 0 2 4 6 8 10 12 14 16 0 1000 2000 3000 4000 5000 slew rate vs. load capacitance max3387e-02 load capacitance (pf) slew rate (v/?) slew rate + slew rate - typical operating characteristics (v cc = v l = +3.3v, t a = +25?, unless otherwise noted.) c l = 150pf to 1000pf c l = 150pf to 2500pf v cc = +3.3v, t a = +25?, r l = 3k to 7k , measured from +3v to -3v or -3v to +3v r l = 3k , c l = 1000pf, one transmitter switching (note 2) v/? 43 0 ? v t_out ? > +3.7v transition-region slew rate receiver input to receiver output, c l = 150pf conditions 63 0 ns 50 ? t phl - t plh ? receiver skew ns 100 ? t phl - t plh ? transmitter skew ? 100 time to exit shutdown ? 0.15 t plh receiver propagation delay kbps 250 maximum data rate 0.15 t phl units min typ max symbol parameter timing characteristics (v cc = v l = +3v to +5.5v; c1?4 = 0.1?, tested at +3.3v ?0%; c1 = 0.047?, c2?4 = 0.33?, tested at +5.0v ?0%; t a = t min to t max , unless otherwise noted. typical values are at v cc = v l = +3.3v, t a = +25?.) max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones 4 _______________________________________________________________________________________ note 2: transmitter skew is measured at the transmitter zero crosspoints. downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones _______________________________________________________________________________________ 5 -7.5 -5.0 -2.5 0 2.5 5.0 7.5 0 50 100 150 200 250 transmitter output voltage vs. data rate max3387e-03 data rate (kbps) output voltage (v) load = 3k , 1000pf one transmitterswitching at data rate, other transmitters at 1/8 data rate 0 10 20 30 40 50 60 0 1000 2000 3000 4000 5000 supply current vs. load capacitance max3387e-04 load capacitance (pf) supply current (ma) 250kbps 120kbps 20kbps load = 3k , one transmitterswitching at data rate, other transmitters at 1/8 data rate typical operating characteristics (continued) (v cc = v l = +3.3v, t a = +25?, unless otherwise noted.) 2423 22 21 20 19 18 17 12 3 4 5 6 7 8 forceoffv cc gndt1out c2+ c1- v+ c1+ top view t2outt3out r1in r2in t2in t1in v- c2- 1615 14 13 9 1011 12 r3inv l r1outr2out r3out forceon t3in invalid tssop max3387e + pin configuration downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones 6 _______________________________________________________________________________________ c1+ positive terminal of the voltage-doubler charge-pump capacitor pin description v+ +5.5v supply generated by the charge pump c1- negative terminal of the voltage-doubler charge-pump capacitor c2+ positive terminal of the inverting charge-pump capacitor c2- negative terminal of the inverting charge-pump capacitor v- -5.5v generated by the charge pump t1in ttl/cmos transmitter inputs r3out ttl/cmos receiver outputs. swing between 0v and v l . r2out r1out v l logic-level supply. all cmos inputs and outputs are referenced to this supply. r3in r2in r1in rs-232 receiver inputs t3out t2out t1out rs-232 transmitter outputs gnd ground v cc +3.0v to +5.5v supply voltage name function forceoff force-off input. drive forceoff low to shut down transmitters and on-board power sup- ply. this overrides all automatic circuitry and forceon (table 1). 1 2 3 4 5 6 7 12 13 14 15 16 17 18 19 20 21 22 23 pin 24 forceon force-on input. drive forceon high to override automatic circuitry keeping transmitterson ( forceoff must be high) (table 1). 11 invalid output of the valid signal detector. invalid is high if a valid rs-232 signal is present on the receiver inputs. 9 t3in ttl/cmos transmitter inputs 10 8 t2in downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones _______________________________________________________________________________________ 7 detailed description dual charge-pump voltage converter the max3387e? internal power supply consists of aregulated dual charge pump that provides output volt- ages of +5.5v (doubling charge pump) and -5.5v (inverting charge pump), regardless of the input volt- age (v cc ) over a +3.0v to +5.5v range. the charge pumps operate in a discontinuous mode: if the outputvoltages 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 fly- ing 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 max3387e transmitters guarantee a 250kbps data rate with worst-case loads of 3k in parallel with 1000pf, providing compatibility with pc-to-pc commu-nication software (such as laplink ). transmitters can be paralleled to drive multiple receivers or mice. figure 1 shows a complete system connection. these rs-232 output stages are turned off (high imped-ance) when the device is in shutdown mode. when the power is off, the max3387e permits the outputs to be driven up to ?2v. the transmitter inputs do not have pull-up resistors. connect unused inputs to gnd or v l . rs-232 receivers the receivers convert rs-232 signals to cmos-logicoutput levels. the max3387e? receivers are always active, even when the device is in shutdown. the max3387e features an invalid output that indi- cates when no signal is present on any rs-232 receiverinputs. invalid is independent of other control logic functions; it indicates the receiver input conditions only(figures 2 and 3). max3387e i/o chip with uart cpu rs-232 power- management unit or keyboard controller v l v cc i/o chip power supply forceoff forceoninvalid figure 1. interface under control of pmu laplink is a registered trademark of laplink software, inc. +0.3v -0.3v invalid r_in transmitters are disabled, reducing supply current to 1 a if all receiver inputs are between +0.3v and -0.3v for at least 30 s. 30 s counter r +2.7v -2.7v invalid r_in transmitters are enabled if:any receiver input is greater than +2.7v or less than -2.7v; any receiver input has been between +0.3v and -0.3v for less than 30 s. 30 s counter r figure 2a. invalid function diagram, invalid = low figure 2b. invalid function diagram, invalid = high downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones 8 _______________________________________________________________________________________ autoshutdown plus mode the max3387e achieves a1? supply current with maxim? autoshutdown plus feature, which operates when forceoff is high and a forceon is low. when these devices do not sense a valid signal transition onany receiver and transmitter input for 30sec, the on- board charge pumps are shut down, reducing supply current to 1?. this occurs if the rs-232 cable is dis- connected or if the connected peripheral transmitters are turned off, and if the uart driving the transmitter inputs is inactive. the system turns on again when a valid transition is applied to any rs-232 receiver or transmitter input. as a result, the system saves power without changes to the existing bios or operating sys- tem. figure 3a shows valid and invalid rs-232 receiver volt- age levels. invalid indicates the receiver input? con- dition, and is independent of forceon and forceoff states. figure 2 and table 1 summarize the max3387e? operating modes. forceon and force- off override autoshutdown plus circuitry. when nei- ther control is asserted, the ic selects between thesestates automatically based on the last receiver or trans- mitter input edge received. by connecting forceon to invalid , the max3387e shuts down when no valid receiver level and no receiver or transmitter edge is detected for 30sec, and wakes upwhen a valid receiver level or receiver or transmitter edge is detected. by connecting forceon and forceoff to invalid , the max3387e shuts down when no valid receiver levelis detected. a mouse or other system with autoshutdown plus may need time to wake up. figure 4 shows a circuit that forces the transmitters on for 100ms, allowing enough time for the other system to realize that the max3387e is awake. if the other system outputs valid rs-232 sig- nal transitions within that time, the rs-232 ports on both systems remain enabled. v l logic supply input unlike other rs-232 interface devices where the receiv-er outputs swing between 0v and v cc , the max3387e features a separate logic supply input (v l ) that sets v oh for the receiver outputs and sets thresholds for the receiver inputs. this feature allows a great deal of flexi-bility in interfacing to many different types of systems with different logic levels. connect this input to the host logic supply (1.8v v l v cc ). also, see the typical pda/cell-phone application section. powerdown autoshdn forceoff forceon powerdown is only an internal signal. it controls the operational status of the transmitters and the power supplies. figure 2c. autoshutdown plus logic receiver input levels -2.7v -0.3v +2.7v+0.3v 0v indeterminate transmitters enabled, invalid high autoshutdown, transmitters disabled, 1 a supply current, invalid low transmitters enabled, invalid high indeterminate figure 3a. receiver thresholds for invalid autoshdn r_in t_in r s 30s timer edge detect edge detect forceoff forceon figure 2d. power-down logic downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones _______________________________________________________________________________________ 9 v cc 0 v+ v- v cc 0 invalid output transmitter inputs receiver inputs } invalidregion transmitter outputs t autoshdn t wu t wu t invl t invh t autoshdn figure 3b. autoshutdown plus/ invalid timing diagram software-controlled shutdown if direct software control is desired, invalid can be used to indicate a dtr or ring indicator signal. connectforceoff and forceon together to bypass autoshutdown so the line acts like a shdn input. 15kv esd protection as with all maxim devices, esd-protection structuresare incorporated on all pins to protect against electro- static discharges (esds) encountered during handling and assembly. the max3387e driver outputs and receiver inputs have extra protection against static electricity. maxim has developed state-of-the-art struc- tures to protect these pins against esd of ?5kv with- out damage. the esd structures withstand high esd in all states: normal operation, shutdown, and powered down. after an esd event, maxim? ??version devices keep working without latchup, whereas competing rs- 232 products can latch and must be powered down to remove latchup. esd protection can be tested in vari- ous ways. the transmitter outputs and receiver inputs of this product family are characterized for protection to the following limits: 1) ?5kv using the human body model 2) ?kv using the contact-discharge method specified in iec 1000-4-2 3) ?5kv using iec 1000-4-2? air-gap method forceon master shdn line 0.1 f1 m forceoff max3387e power- management unit figure 4. autoshutdown with initial turn-on to wake up a system downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones 10 ______________________________________________________________________________________ esd test conditions esd performance depends on a variety of conditions.contact maxim for a reliability report that documents test setup, methodology, and results. human body model figure 5a shows the human body model, and figure5b shows the current waveform it generates when dis- charged into a low impedance. this model consists of a 100pf capacitor charged to the esd voltage of interest, which is then discharged into the test device through a 1.5k resistor. table 1. output control truth table operation status forceon forceoff valid receiver level receiver or transmitter edge within 30 t_out r_out shutdown (forced off) x 0 x x high-z active normal operation (forced on) 1 1 x x active active normal operation (autoshutdown plus) 0 1 x yes active active shutdown (autoshutdown plus) 0 1 x no high-z active normal operation invalid 1 yes x active active normal operation invalid 1 x yes active active shutdown invalid 1 no no high-z active normal operation (autoshutdown) invalid invalid yes x active active shutdown(autoshutdown) invalid invalid no x high-z active charge-current limit resistor discharge resistance storagecapacitor c s 100pf r c 1m r d 1500 high- voltage dc source device under test figure 5a. human body esd test model i p 100% 90% 36.8% t rl time t dl current waveform peak-to-peak ringing(not drawn to scale) i r 10% 0 0 amperes figure 5b. human body current waveform x = don? care downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones ______________________________________________________________________________________ 11 iec 1000-4-2 the iec 1000-4-2 standard covers esd testing andperformance of finished equipment; it does not specifi- cally refer to ics. the max3387e helps you design equipment that meets level 4 (the highest level) of iec 1000-4-2, without the need for additional esd-protec- tion components. the major difference between tests done using the human body model and iec 1000-4-2 is higher peak current in iec 1000-4-2 because series resistance is lower in the iec 1000-4-2 model. hence, the esd with- stand voltage measured to iec 1000-4-2 is generally lower than that measured using the human body model. figure 6a shows the iec 1000-4-2 model, and figure 6b shows the current waveform for the ?kv iec 1000-4-2 level 4 esd contact discharge test. the air-gap test involves approaching the device with a charged probe. the contact-discharge method connects the probe to the device before the probe is energized. machine model the machine model for esd tests all pins using a 200pf storage capacitor and zero discharge resis- tance. its objective is to emulate the stress caused by contact that occurs with handling and assembly during manufacturing. all pins require this protection during manufacturing, not just rs-232 inputs and outputs. therefore, after pc board assembly, the machine model is less relevant to i/o ports. applications information capacitor selection the capacitor type used for c1?4 is not critical forproper operation; polarized or nonpolarized capacitors can be used. the charge pump requires 0.1? capaci- tors for 3.3v operation. for other supply voltages, seetable 2 for required capacitor values. do not use val- ues smaller than those listed in table 2. 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, and c4 to maintain the proper ratios (c1 to the other capacitors). 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? equiva- lent series resistance (esr), which usually rises at low temperatures, influences the amount of ripple on v+ and v-. charge-current limit resistor discharge resistance storagecapacitor c s 150pf r c 50m to 100m r d 330 high- voltage dc source device under test figure 6a. iec 1000-4-2 esd test model t r = 0.7ns to 1ns 30ns 60ns t 100% 90%10% i peak i figure 6b. iec 1000-4-2 esd generator current waveform table 2. minimum required capacitorvalues v cc (v) 0.1 0.1 c2, c3, c4 (?) 3.0 to 3.6 0.33 0.047 1 0.22 3.0 to 5.5 4.5 to 5.5 c1 (?) downloaded from: http:///
max3387e power-supply decoupling in most circumstances, a 0.1? bypass capacitor is ade-quate. in applications that are sensitive to power-supply noise, decouple v cc to ground with a capacitor of the same value as charge-pump capacitor c1. connectbypass capacitors as close to the ic as possible. operation down to 2.7v transmitter outputs will meet tia/eia-562 levels of?.7v with supply voltages as low as +2.7v. transmitter outputs when exiting shutdown figure 7 shows two transmitter outputs when exitingshutdown mode. as they become active, the two trans- mitter outputs are shown going to opposite rs-232 lev- els (one transmitter input is high; the other is low). each transmitter is loaded with 3k in parallel with 2500pf. the transmitter outputs display no ringing or undesir-able 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 max3387e maintains the rs-232 ?.0v minimumtransmitter output voltage even at high data rates. figure 8 shows a transmitter loopback test circuit. figure 9 shows a loopback test result at 120kbps, and figure 10 shows the same test at 250kbps. for figure 9, all transmitters were driven simultaneously at 120kbps into rs-232 loads in parallel with 1000pf. for figure 10, a single transmitter was driven at 250kbps, and all transmitters were loaded with an rs-232 receiv- er in parallel with 1000pf. interconnection with 3v and 5v logic the max3387e can directly interface with various 5vlogic families, including act and hct cmos. the logic voltage power-supply pin (v l ) sets the output voltage level of the receivers and the input thresholds of thetransmitters. 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones 12 ______________________________________________________________________________________ max3387e 5k r_ in r_ out c2- c2+ c1- c1+ v- v+ v cc c4 c3 c1 c2 0.1 f v cc forceon forceoff t_ out t_ in gnd v cc 1000pf figure 8. loopback test circuit 2 s/div t1in t1out r1out 5v/div5v/div 5v/div v cc = 3.3v figure 9. loopback test results at 120kbps 50 s/div t2 t1 5v/div2v/div v cc = 3.3v c1?4 = 0.1 f figure 7. transmitter outputs when exiting shutdown downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones ______________________________________________________________________________________ 13 typical pda/cell-phone application the max3387e is designed with pda applications inmind. two transmitters and two receivers handle stan- dard full-duplex communication protocol, while an extra transmitter allows a ring indicator signal to alert the uart on the pc. without the ring indicator transmitter, solutions for these applications would require software- intensive polling of the cradle inputs. the ring indicate (ri) signal is generated when a pda, phone, or other ?radled?device is plugged into its cradle. this generates a logic-low signal to the ri transmitter input, creating +6v at the ring indicate pin. the pc? uart ri input is the only pin that can generate an inter- rupt from signals arriving through the rs-232 port. the interrupt routine for this uart will then service the rs- 232 full-duplex communication between the pda and the pc. as cell phone design becomes more like that of pdas,cell phones will require similar docking ability and com- munication protocol. cell phones operate on a single lithium-ion (li+) battery and work with a power-supply voltage of +2.7v to +4v. the baseband logic coming from the phone connector can be as low as 1.8v at the transceivers. to prevent forward biasing of a device internal to the cell phone, the max3387e comes with a logic power-supply pin (v l ) that limits the logic levels presented to the phone. the receiver outputs will sinkto zero for low outputs, but will not exceed v l for logic highs. the input logic levels for the transmitters are alsoaltered, scaled by the magnitude of the v l input. the device will work with v l as low as 1.8v before the charge-pump noise will begin to cause the transmitteroutputs to oscillate. this is useful with cell phones and other power-efficient devices with core logic voltage levels that go as low as 1.8v. chip information process: bicmos package information for the latest package outline information and land patterns,go to www.maxim-ic.com/packages . note that a ?? ?? or ??in the package code indicates rohs status only. packagedrawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. 2 s/div t1in t1out r1out 5v/div5v/div 5v/div v cc = 3.3v figure 10. loopback test results at 250kbps package type package code document no. 24 tssop u24+1 21-0066 downloaded from: http:///
max3387e 3v, 15kv esd-protected, autoshutdown plus rs-232 transceiver for pdas and cell phones 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. 14 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2010 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history reision number reision date description pages changed added note 2 to the elecrical characerisics table 4 3 6/10 changed the chip informaion section to say process: bicmos 13 downloaded from: http:///

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