general description the MAX9940 signal-line overvoltage protector for low- voltage digital communication ports provides protection against high-voltage faults and esd strikes. the MAX9940 is especially useful for sensitive communica- tion protocols such as maxim 1-wire that cannot afford standard means of fault protection, such as large series resistors or large line capacitances. the MAX9940 operates from a single supply voltage of +2.2v to +5.5v and consumes only 13? of quiescent supply current. the ext port is protected up to 28v. the device features a reaction time of 60ns for fast action during fault conditions and operates over the -40? to +125? automotive temperature range. applications notebook computers portable devices industrial equipment features ? 28v protection on ext ? extended esd protection ?kv iec 61000-4 contact on ext ? +2.2v to +5.5v supply voltage range ? 13? quiescent supply current ? 60ns fault reaction time ? small, 5-pin sc70 ? -40? to +125? temperature range MAX9940 signal-line overvoltage protector for low-voltage devices ________________________________________________________________ maxim integrated products 1 19-4168; rev 0; 2/09 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. notebook adapter microcontroller ext gnd int 1-wire device 2k 20v + - n protection circuit enable v cc data p notebook battery charger load v dd = 3.3v MAX9940 rx tx rx tx block diagram/typical application circuit ordering information part temp range pin- package top mark MAX9940axk+ -40? to +125? 5 sc70 atc + denotes a lead(pb)-free/rohs-compliant package. 1-wire is a registered trademark of maxim integrated products, inc.
MAX9940 signal-line overvoltage protector for low-voltage devices 2 _______________________________________________________________________________________ absolute maximum ratings 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. (all voltages with respect to gnd.) v cc ...........................................................................-0.3v to +6v int ............................................................................-0.3v to +6v ext .........................................................................-0.3v to +30v continuous input current into any terminal.....................?0ma continuous power dissipation (t a = +70?) 5-pin sc70 (derate 3.1mw/? above +70?) ..............245mw operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? parameter symbol conditions min typ max units power supply power-supply voltage v cc 2.2 5.5 v quiescent supply current i cc v int = 0 13 21 a dc characteristics int voltage range v int 0 5.5 v ext voltage range v ext (note 2) -0.7 +28 v ext rising threshold v thr v cc + 0.19 v cc + 0.26 v cc + 0.30 v ext falling threshold v thf v cc + 0.09 v cc + 0.13 v cc + 0.16 v switch characteristics on-resistance r on 0 < v ext < v cc , i ext = ?0ma 43.5 77.5 on-capacitance c on capacitance to gnd 38 pf int off-capacitance c off capacitance to gnd 27 pf int normal operation leakage current (to gnd) 0 < v int < v cc , v cc = 5.5v 3 4.2 ? ext normal operation leakage current (to gnd) 0 < v ext < v cc , v cc = 5.5v 3 5 ? int fault leakage current v int = 3.3v, v ext = 28v 2 10 na ext fault leakage current v int = 3.3v, v ext = 28v 341 510 ? v cc = v dd = 0, 2.2v < v dd < 5.5v, r int_pullup = 2k to v dd 38 70 ? int shutdown leakage current (to gnd) v cc = v dd = 0 1 na ac characteristics power-up delay time t pup 500 ? fault, v ext = 10v, r int_pullup = 200 98 200 fault reaction time t off fault, v ext = 16v, r int_pullup = 200 60 ns fault recovery time t on fault removed, v ext < v cc - 0.8v 271 375 ns note 1: all devices are 100% production tested at t a = +25?. specifications over temperature limits are guaranteed by design. note 2: minimum ext voltage of -0.7v is allowed only with a maximum drawn current of 20ma. electrical characteristics (v cc = +3.3v, r int_pullup = 2k to v dd , v dd = 3.3v, t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1)
MAX9940 signal-line overvoltage protector for low-voltage devices _______________________________________________________________________________________ 3 0 20 10 40 30 50 60 023 1456 on-resistance vs. v cm MAX9940 toc01 v cm (v) on-resistance ( ) v cc = 2.5v v cc = 3.3v v cc = 5.5v 0 10 20 30 40 50 60 01.0 0.5 1.5 2.0 2.5 3.0 3.5 4.0 on-resistance vs. v cm MAX9940 toc02 v cm (v) on-resistance ( ) t a = +125 c t a = +85 c t a = +25 c t a = -40 c 0 50 100 150 200 250 300 -50 0 -25 25 50 75 100 125 150 turn-on/turn-off time vs. temperature MAX9940 toc03 temperature ( c) turn-on/turn-off time (ns) turn-on turn-off ext = 0 to 10v square wave r pullup = 200 0 50 100 150 200 250 300 -50 0 -25 25 50 75 100 125 150 turn-on/turn-off time vs. temperature MAX9940 toc04 temperature ( c) turn-on/turn-off time (ns) turn-on turn-off ext = 0 to 16v square wave r pullup = 200 12.0 13.0 12.5 14.0 13.5 14.5 15.0 15.5 16.0 2.0 3.0 3.5 2.5 4.0 4.5 5.0 5.5 6.0 supply current vs. supply voltage MAX9940 toc05 supply voltage (v) supply current ( a) t a = +125 c t a = +85 c t a = +25 c t a = -40 c insertion loss vs. frequency MAX9940 toc06 frequency (hz) insertion loss (db) 10m 1m 100k 10k -6 -5 -4 -3 -2 -1 0 1 2 3 -7 1k 100m off-isolation vs. frequency MAX9940 toc07 frequency (hz) off-isolation (db) 10m 1m 100k 10k -100 -80 -60 -40 -20 0 -120 1k 100m int 500mv/div ext 1v/div time (40 fault turn-on and recovery time MAX9940 toc08 v dd = v cc = 3.3v 0 0 typical operating characteristics (v cc = +3.3v, r int_pullup = 2k to v dd , v dd = 3.3v, t a = t min to t max , unless otherwise noted.)
MAX9940 signal-line overvoltage protector for low-voltage devices 4 _______________________________________________________________________________________ typical operating characteristics (continued) (v cc = +3.3v, r int_pullup = 2k to v dd , v dd = 3.3v, t a = t min to t max , unless otherwise noted.) fault recovery time MAX9940 toc10 time (100ns/div) int 500mv/div ext 5v/div r pullup = 2k 0 0 fault turn-on and recovery time (schottky diode from int to v cc ) MAX9940 toc11 time (40 s/div) int 1v/div ext 5v/div r pullup = 2 0 0 fault turn-on time (schottky diode from int to v cc ) MAX9940 toc12 time (100ns/div) int 1v/div ext 5v/div 0 0 0 50 100 150 200 250 300 2.0 3.0 2.5 3.5 4.0 4.5 5.0 5.5 6.0 v thr and v thf vs. supply voltage MAX9940 toc13 supply voltage (v) voltage threshod (mv) v thr v thf 0 100 50 200 150 250 300 -50 25 50 -25 0 75 100 125 v thr and v thf vs. temperature MAX9940 toc14 temperature ( c) voltage threshold (mv) v thr v thf fault turn-on time MAX9940 toc09 time (100ns/div) int 2v/div ext 5v/div r pullup = 200 0 0
detailed description the MAX9940 is a signal-line overvoltage protector for low-voltage devices that provides circuit protection from high-voltage faults and esd strikes. the device provides protection in digital communication lines such as 1-wire and i 2 c protocols where large series resis- tance and capacitances cannot be used to provide protection due to their impact on v il /v ih levels and communication timing. the MAX9940 includes a series switch that connects int to ext. when a high-voltage fault condition occurs on ext, the MAX9940 quickly shuts off the series switch and isolates the low-voltage device from the fault condition. in addition to providing dc fault isolation, the MAX9940 also provides up to ?kv iec 61000-4 contact esd protection on ext. the MAX9940 is ideal for circuits that require low-voltage devices that communicate to the outside world over connector ports that can expose them to hazardous high-voltage dc faults and esd strikes. series switch the MAX9940 features a series switch to connect a low-voltage device such as a microcontroller to an external communication device such as a 1-wire or i 2 c slave. the internal switch is turned off when disabled or if a fault condition exists, isolating the microcontroller from any possible damage. the nominal switch resis- tance is 38 (typ). the series switch is composed of parallel dmos and hv-pmos devices as shown in the block diagram/typical application circuit . the series switch cell contains circuitry that ensures the pmos device turns off properly when the voltage at ext exceeds the supply voltage. the switch can withstand a maximum voltage of 28v at ext. comparator the MAX9940 features a low-power, high-speed com- parator that is used to turn off the series switch if a high-voltage condition is detected on ext. the nominal hysteresis of the comparator is 128mv (typical). fault voltages on ext that are slightly above v cc trigger the comparator to quickly isolate int and ext channels from each other. in this mode, the MAX9940 is able to withstand 28v on ext. negative voltages on ext are allowed as long as they are current-limited to less than 20ma. typical application circuits the innovative design of the MAX9940 allows it to with- stand large dc voltages up to 28v at int and ext even when v cc is 0. this allows application-specific power- saving and fault-protection schemes to be implemented. figures 1 and 2 show two methods of powering the MAX9940 from an enable digital output port of the microcontroller. figure 3 shows the conventional method of operating the MAX9940 with both pullup resistor for digital communication on data (rp) and v cc being connected directly to v dd of the microcontroller. MAX9940 signal-line overvoltage protector for low-voltage devices _______________________________________________________________________________________ 5 _______________________________________________________________________________________ 5 pin description pin name function 1v cc power supply. can be connected to a microcontroller enable input. 2 gnd ground 3 n.c. no connection. not internally connected. 4 int microcontroller i/o port. connection to a microcontroller data port. 5 ext external connector port. connection to a 1-wire device.
MAX9940 in all three schemes, the MAX9940 protects the micro- controller from both dc fault voltages above v cc and esd strikes on ext. the difference in the three schemes lies in the impact on power consumption in battery-operated devices during normal and short to gnd fault conditions. figure 1 shows a recommended configuration for battery- operated devices that need to conserve power both on a continuous basis as well as during short to gnd fault conditions. in this scheme, the enable port of a micro- controller supplies the quiescent current for the MAX9940 as well as that required for digital communi- cation (i.e., r p pullup resistor). by forcing a 0 on the enable digital output port of the microcontroller, the MAX9940 is in a zero-power shutdown mode, while also preventing any power drain to occur in the event of a short to gnd fault on ext. as stated earlier, ext main- tains the ability to withstand dc voltages up to 28v even when v cc = 0. in figure 2, the enable port of a microcontroller pow- ers the MAX9940. the low 13? operating current allows standard digital i/o ports to easily supply the operating current of the MAX9940 without any substan- tial voltage drop (v oh v dd ). by forcing a 0 on the enable port of the microcontroller, the MAX9940 can be put into a zero-power mode, thus conserving battery power. it should be noted that there is no internal esd diode from int to v cc . this allows the voltage at int to stay at v dd even though v cc = 0, thus drawing no cur- rent from r p or the battery. however, an internal diode does exist from int to ext, and therefore, in the event of a short to gnd fault on ext, current is drawn through r p , causing a power drain from v dd , and can potential- ly reduce battery life. in figure 3, v dd powers the MAX9940 directly, and consumes quiescent current on a continuous basis. in this mode, the internal fet between int and ext is kept on as long as the voltage on ext is below v cc . as a result, in the event of a short to gnd fault on ext, current is drawn through rp, causing a power drain from v dd and potentially reducing battery life. signal-line overvoltage protector for low-voltage devices 6 _______________________________________________________________________________________ microcontroller ext gnd int enable v cc r p 2k v dd = 3.3v MAX9940 data rx tx 1-wire device rx tx figure 1. recommended scheme for battery-operated devices that need to shut down the MAX9940 and prevent power draw during short to gnd faults
MAX9940 signal-line overvoltage protector for low-voltage devices _______________________________________________________________________________________ 7 microcontroller ext gnd int v cc r p 2k v dd = 3.3v MAX9940 data rx tx 1-wire device rx tx figure 3. recommended operating circuit for nonbattery-operated applications microcontroller ext gnd int enable v cc r p 2k v dd = 3.3v MAX9940 1-wire device rx tx data rx tx figure 2. recommended scheme for applications that require the MAX9940 to be put into shutdown
MAX9940 signal-line overvoltage protector for low-voltage devices 8 _______________________________________________________________________________________ gnd int n.c. 1 5 ext v cc MAX9940 sc70 + top view 2 34 pin configuration chip information process: bicmos
MAX9940 signal-line overvoltage protector for low-voltage devices 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. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 _____________________ 9 2009 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. package type package code document no. 5 sc70 x5-1 21-0076 package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . sc70, 5l.eps package outline, 5l sc70 21-0076 1 1 e
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