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general description the max6643/max6644/max6645 monitor temperatureand automatically adjust fan speed to ensure optimum cooling while minimizing acoustic noise from the fan. each device measures two temperature locations. the max6643/max6644/max6645 generate a pwm waveform that drives an external power transistor, which in turn modulates the fan? power supply. the max6643/max6644/max6645 monitor temperature and adjust the duty cycle of the pwm output waveform to con- trol the fan? speed according to the cooling needs of the system. the max6643 monitors its own die temperature and an optional external transistor? temperature, while the max6644 and max6645 each monitor the temperatures of one or two external diode-connected transistors. the max6643 and max6644 have nine selectable trip temperatures (in 5 c increments). the max6645 is fac- tory programmed and is not pin selectable. all versions include an overtemperature output ( ot ). ot can be used for warning or system shutdown. the max6643 also features a fullspd input that forces thepwm duty cycle to 100%. the max6643/max6644/ max6645 also feature a fanfail output that indicates a failed fan. see the selector guide for a complete list of each device? functions.the max6643 and max6644 are available in a small 16-pin qsop package and the max6645 is available in a 10-pin ?ax package. all versions operate from 3.0v to 5.5v supply voltages and consume 500? (typ)supply current. applications networking equipmentstorage equipment servers desktop computers workstations features ? simple, automatic fan-speed control ? internal and external temperature sensing ? detect fan failure through locked-rotor output,tachometer output, or fan-supply current sensing ? multiple, 1.6% output duty-cycle steps for lowaudibility of fan-speed changes ? pin-selectable or factory-selectable low-temperature fan threshold ? pin-selectable or factory-selectable high-temperature fan threshold ? spin-up time ensures fan start ? fan-start delay minimizes power-supply load atpower-up ? 32hz pwm output ? controlled duty-cycle rate-of-change ensuresgood acoustic performance ? 2 c temperature-measurement accuracy ? fullspd/ fullspd input sets pwm to 100% ? pin-selectable ot output threshold ? 16-pin qsop and 10-pin max packages max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output ________________________________________________________________ maxim integrated products 1 ordering information 19-3305; rev 2; 3/07for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available pin configurations, typical operating circuit, and selectorguide appear at end of data sheet. part temp range pin-package pkg code max6643 lbfaee -40 c to +125 c 16 qsop e16-1 max6643lbbaee -40 c to +125 c 16 qsop e16-1 max6644 lbaaee -40 c to +125 c 16 qsop e16-1 max6645 abfaub -40 c to +125 c 10 ?ax u10-2 ?ax is a registered trademark of maxim integrated products, inc. downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics(v dd = +3.0v to +5.5v, t a = -40 c to +125 c, unless otherwise noted. typical values are at v dd = +3.3v, t a = +25?.) (note 1) 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 dd to gnd ..............................................................-0.3v to +6v pwm_out, ot , and fanfail to gnd.....................-0.3v to +6v fan_in1 and fan_in2 to gnd...........................-0.3v to +13.2v dxp_ to gnd.........................................................-0.3v to +0.8v fullspd, fullspd , th_, tl_, tachset, and ot_ to gnd ..................................-0.3v to +(v dd + 0.3v) fanfail , ot current ..........................................-1ma to +50ma continuous power dissipation (t a = +70?) 16-pin qsop (derate 8.3mw/? above +70?).......... 667mw 10-pin ?ax (derate 5.6mw/? above +70?) ...........444mw operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range ............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units operating supply voltage range v dd +3.0 +5.5 v t a = +20? to +60? ? remote temperature error v dd = +3.3v, +20 c t rj +100 c t a = 0? to +125? ? c t a = +10? to +70? ?.5 local temperature error v cc = +3.3v t a = 0? to +125? ?.5 c temperature error from supplysensitivity ?.2 c/v power-on-reset (por) threshold v dd falling edge 1.5 2.0 2.5 v por threshold hysteresis 90 mv operating current i s during a conversion 0.5 1 ma average operating current duty cycle = 50%, no load 0.5 ma remote-diode sourcing current high level 80 100 120 ? conversion time 125 ms spin-up time max664_ _b_ _ _ _ 8 s startup delay max664_ _b_ _ _ _ 0.5 s minimum fan-fail tachometerfrequency 16 hz pwm_out frequency f pwm_out 32 hz digital outputs ( ot , fanfail , pwm_out) output low voltage ( ot )v ol i sink = 1ma 0.4 v i sink = 6ma 0.5 output low voltage( fanfail , pwm_out) v ol i sink = 1ma 0.4 v output-high leakage current i oh v oh = 3.3v 1 a downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output _______________________________________________________________________________________ 3 operating supply current vs. supply voltage max6643 toc01 supply voltage (v) supply current ( a) 5.0 4.5 4.0 3.5 240 280 320 360 400200 3.0 5.5 pwmout frequency vs. die temperature max6643 toc02 temperature ( c) pwmout frequency (hz) 100 85 60 35 10 -15 31.2 31.4 31.6 31.8 32.031.0 -40 trip-threshold error vs. trip temperature max6643 toc04 trip temperature ( c) trip-threshold error ( c) 80 60 40 -0.6 -0.2 0.2 0.6 1.0 -1.0 20 100 max664_l versions pwmout frequency vs. supply voltage max6643 toc03 supply voltage (v) pwmout frequency (hz) 5.0 4.5 4.0 3.5 31 32 33 34 3530 3.0 5.5 typical operating characteristics (t a = +25?, unless otherwise noted.) electrical characteristics (continued)(v dd = +3.0v to +5.5v, t a = -40 c to +125 c, unless otherwise noted. typical values are at v dd = +3.3v, t a = +25?.) (note 1) parameter symbol conditions min typ max units digital inputs ( fullspd , fullspd, tachset) v dd = 5.5v 3.65 logic-input high v ih v dd = 3.0v 2.2 v logic-input low v il v dd = 3.0v 0.8 v input leakage current v in = gnd or v dd -1 +1 ? note 1: all parameters tested at t a = +25?. specifications over temperature are guaranteed by design. downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output 4 _______________________________________________________________________________________ pin description pin max6643 max6644 max6645 name function 1, 15 1, 15 th1, th2 high-temperature threshold inputs. connect to v dd , gnd, or leave unconnected to select the upper fan-control triptemperature (t high ), in 5? increments. see table 1. 2, 3 2, 3 tl2, tl1 low-temperature threshold inputs. connect to v dd , gnd, or leave unconnected to select the lower fan-control triptemperature (t low ), in 5? increments. see table 2. 441 fanfail fan-fail alarm output. fanfail is an active-low, open-drain output. if the fan_in_ detects a fan failure, the fanfail output asserts low. 5 5 2 tachset fan_in_ control input. tachset controls what type of fan-failcondition is being detected. connect tachset to v dd , gnd, or leave floating to set locked rotor, current sense, ortachometer configurations (see table 3). 6 fullspd active-high logic input. when pulled high, the fan runs at100% duty cycle. fullspd active-low logic input. when pulled low, the fan runs at 100%duty cycle. 7 7 4 gnd ground 8 dxp 6, 8 3, 5 dxp2, dxp1 c om b i ned c ur r ent s our ce and a/d p osi ti ve inp ut for rem ote d i od e. c onnect to anod e of r em ote d i od e- connected tem p er atur e- sensi ng tr ansi stor . c onnect to g n d i f no r em ote d i od e i s used . p l ace a 2200p f cap aci tor b etw een d x p _ and g n d for noi se fi l ter i ng . 996 ot active-low, open-drain overtemperature output. when ot threshold is exceeded, ot pulls low. 10, 11 10, 11 7, 8 fan_in2, fan_in1 fan- s ense inp ut. fan _in _ can b e confi g ur ed to m oni tor ei ther a fan s l og i c- l evel l ocked - r otor outp ut, tachom eter outp ut, or sense- r esi stor w avefor m to d etect fan fai l ur e. the m ax 6643 s fan _in _ i np ut can m oni tor onl y tachom eter si g nal s. the m ax 6644 and the m ax 6645 can m oni tor any one of the thr ee si g nal typ es as confi g ur ed usi ng the tac h s e t i np ut. downloaded from: http:///
detailed description the max6643/max6644/max6645 measure temperatureand automatically adjust fan speed to ensure optimum cooling while minimizing acoustic noise from the fan. the max6643/max6644/max6645 generate a pwm waveform that drives an external power transistor, which in turn modulates the fan? power supply. the max6643/max6644/max6645 monitor temperature and adjust the duty cycle of the pwm output waveform to control the fan? speed according to the cooling needs of the system. the max6643 monitors its own die tem- perature and an optional external transistor? tempera- ture, while the max6644 and max6645 each monitor the temperatures of one or two external diode-connect- ed transistors. temperature sensor the pn junction-based temperature sensor can mea-sure temperatures up to two pn junctions. the max6643 measures the temperature of an external diode-connected transistor, as well as its internal tem- perature. the max6644 and max6645 measure the temperature of two external diode-connected transis- tors. the temperature is measured at a rate of 1hz. if an external ?iode?pin is shorted to ground or left unconnected, the temperature is read as 0?. since the larger of the two temperatures prevails, a faulty or unconnected diode is not used for calculating fan speed or determining overtemperature faults. pwm output the larger of the two measured temperatures is alwaysused for fan control. the temperature is compared to three thresholds: the high-temperature threshold (t high ), the low-temperature threshold (t low ), and the overtem- perature threshold, ot . the ot comparison is done once per second, whereas the comparisons with fan-controlthresholds t high and t low are done once every 4s. the duty-cycle variation of pwm_out from 0% to 100%is divided into 64 steps. if the temperature measured exceeds the threshold t high , the pwm_out duty cycle is incremented by one step, i.e., approximately 1.5%(100/64). similarly, if the temperature measured is below the threshold t low , the duty cycle is decremented by one step (1.5%). since the t high and t low compar- isons are done only once every 4s, the maximum rate ofchange of duty cycle is 0.4% per second. tables 1 and 2 show the ? value assigned to the th_ and tl_ input combinations. max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output _______________________________________________________________________________________ 5 pin description (continued) pin max6643 max6644 max6645 name function 12 12 9 pwm_out pwm output for driving external power transistor. connect tothe gate of an n-channel mosfet or to the base of an npn. pwm_out requires a pullup resistor. the pullup resistor can be connected to a supply voltage as high as 5.5v, regardless of the supply voltage. 13, 14 13, 14 ot2, ot1 overtemperature threshold inputs. connect to v dd , gnd, or leave unconnected to select the upper-limit ot fault output trip temperature, in 5? increments. see table 4. 16 16 10 v dd power-supply input. 3.3v nominal. bypass v dd to gnd with a 0.1? capacitor. th2 th1 t high (?) l suffix t high (?) h suffix 0 0 20 40 0 high-z 25 45 0 1 30 50 high-z 0 35 55 high-z high-z 40 60 high-z 1 45 65 1 0 50 70 1 high-z 55 75 1 1 60 80 table 1. setting t high (max6643 and max6644) high-z = high impedance. downloaded from: http:///
max6643/max6644/max6645 there are two options for the behavior of the pwm out-puts at power-up. option 1 (minimum duty cycle = 0): at power-up, the pwm duty cycle is zero. option 2 (minimum duty cycle = the start duty cycle): at power- up, there is a startup delay, after which the duty cycle goes to 100% for the spin-up period. after the startup delay and spin-up, the duty cycle drops to its minimum value. the minimum duty cycle is in the 0% to 50% range (see the selector guide ). to control fan speed based on temperature, t high is set to the temperature beyond which the fan should spinat 100%. t low is set to the temperature below which the duty cycle can be reduced to its minimum value.after power-up and spin-up (if applicable), the duty cycle reduces to its minimum value (either 0% or the start duty cycle). for option 1 (minimum duty cycle = 0), if the measured temperature remains below t high , the duty cycle remains at zero (see figure 1). if the temper-ature increases above t high , the duty cycle goes to 100% for the spin-up period, and then goes to the startduty cycle (for example, 40%). if the measured temper- ature remains above t high when temperature is next measured (4s later), the duty cycle begins to increase,incrementing by 1.5% every 4s until the fan is spinning fast enough to reduce the temperature below t high . for option 2 (minimum duty cycle = start duty cycle), ifthe measured temperature remains below t high , the duty cycle does not increase and the fan continues torun at a slow speed. if the temperature increases above t high , the duty cycle begins to increase, incre- menting by 1.5% every 4s until the fan is spinning fastenough to reduce the temperature below t high (see figure 2). in both cases, if only a small amount of extracooling is necessary to reduce the temperature below automatic pwm fan-speed controllers with overtemperature output 6 _______________________________________________________________________________________ table 2. setting t low (max6643 and max6644) startup duty cycle temperature time time t high spin-up t low figure 1. temperature-controlled duty-cycle change withminimum duty cycle 30% startup max664_b has 30% pwm_out duty cycle during startup. duty cycle temperature timetime t high t low spin-up figure 2. temperature-controlled duty-cycle change withminimum duty cycle 30% tl2 tl1 t low (?) l suffix 001 5 0 high-z 20 012 5 high-z 0 30 high-z high-z 35 high-z 1 40 104 5 1 high-z 50 115 5 high-z = high impedance. downloaded from: http:///
t high , the duty cycle may increase just a few percent above the minimum duty cycle. if the power dissipation orambient temperature increases to a high-enough value, the duty cycle may eventually need to increase to 100%. if the ambient temperature or the power dissipation reduces to the point that the measured temperature is less than t low , the duty cycle begins slowly decre- menting until either the duty cycle reaches its minimumvalue or the temperature rises above t low . the small duty-cycle increments and slow rate-of-change of duty cycle (1.5% maximum per 4s) reduce the likelihood that the process of fan-speed control is acoustically objectionable. the ?ead band?between t low and t high keeps the fan speed constant when the temperature is undergoing small changes, thusmaking the fan-control process even less audible. fan-fail sensing the max6643/max6644/max6645 feature a fanfail output. the fanfail output is an active-low, open- drain alarm. the max6643/max6644/max6645 detectfan failure either by measuring the fan? speed and rec- ognizing when it is too low, or by detecting a locked- rotor logic signal from the fan. fan-failure detection is enabled only when the duty cycle of the pwm drive sig- nal is equal to 100%. this happens during the spin-up period when the fan first turns on and whenever the temperature is above t high long enough that the duty cycle reaches 100%. many fans have open-drain tachometer outputs that produce periodic pulses (usually two pulses per revolu- tion) as the fan spins. these tachometer pulses are monitored by the fan_in_ inputs to detect fan failures. if a 2-wire fan with no tachometer output is used, the fan? speed can be monitored by using an external sense resistor at the source of the driving fet (see figure 3). in this manner, the variation in the current flowing through the fan develops a periodic voltage waveform across the sense resistor. this periodic waveform is then highpass filtered and ac-coupled to the fan_in_ input. any variations in the waveform that have an amplitude of more than ?50mv are converted to digital pulses. the frequency of these digital pulses is directly related to the speed of the rotation of the fan and can be used to detect fan failure. note that the value of the sense resistor must be matched to the characteristics of the fan? current waveform. choose a resistor that produces voltage variations of at least ?00mv to ensure that the fan? operation can be reliably detected. note that while most fans have current waveforms that can be used with this detection method, there may be some that do not produce reliable tachometer signals. if a 2-wire fanis to be used with fault detection, be sure that the fan is compatible with this technique. to detect fan failure, the analog sense-conditioned pulses or the tachometer pulses are deglitched and counted for 2s while the duty cycle is 100% (either dur- ing spin-up or when the duty cycle rises to 100% due to measured temperature). if more than 32 pulses are counted (corresponding to 480rpm for a fan that pro- duces two pulses per revolution), the fan is assumed to be functioning normally. if fewer than 32 pulses are received, the fanfail output is enabled and the pwm duty cycle to the fet transistor is either shut down incase of a single-fan (max6643) configuration or contin- ues normal operation in case of a dual-fan configuration (max6644/max6645). some fans have a locked-rotor logic output instead of a tachometer output. if a locked-rotor signal is to be used to detect fan failure, that signal is monitored for 2s while the duty cycle is 100%. if a locked-rotor signal remains active (low) for more than 2s, the fan is assumed to have failed. the max6643/max6644/max6645 have two channels for monitoring fan-failure signals, fan_in1 and fan_in2. for the max6643, the fan_in_ channels monitor a tachometer. the max6643? fault sensing can also be turned off by floating the tachset input. for the max6644 and max6645, the fan_in1 and fan_in2 channels can be configured to monitor either a logic-level tachometer signal, the voltage waveform on a current-sense resistor, or a locked-rotor logic sig- nal. the tachset input selects which type of signal is to be monitored (see table 3). to disable fan-fault sensing, tachset should be unconnected and fan_in1 and fan_in2 should be connected to v dd . ot output the max6643/max6644/max6645 include an over-temperature output that can be used as an alarm or a system-shutdown signal. whenever the measured tem- perature exceeds the value selected using the ot pro- gramming inputs ot1 and ot2 (see table 4), ot is asserted. ot deasserts only after the temperature drops below the threshold. fullspd input the max6643 features a fullspd input. pulling full-spd high forces pwm_out to 100% duty cycle. the fullspd input allows a microcontroller to force the fan to full speed when necessary. by connecting fanfail to an inverter, the max6643 can force other fans to100% in multifan systems, or for an over-temperature condition (by connecting ot inverter to fullspd). max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output _______________________________________________________________________________________ 7 downloaded from: http:///
max6643/max6644/max6645 applications information figures 3? show various configurations. remote-diode considerations when using an external thermal diode, temperatureaccuracy depends upon having a good-quality, diode- connected, small-signal transistor. accuracy has been experimentally verified for a variety of discrete small- signal transistors, some of which are listed in table 5. the max6643/max6644/max6645 can also directly measure the die temperature of cpus and other ics with on-board temperature-sensing diodes. the transistor must be a small-signal type with a rela- tively high forward voltage. this ensures that the input voltage is within the adc input voltage range. the for- ward voltage must be greater than 0.25v at 10? at the highest expected temperature. the forward voltage must be less than 0.95v at 100? at the lowest expect- ed temperature. the base resistance has to be less than 100 . tight specification of forward-current gain (+50 to +150, for example) indicates that the manufac-turer has good process control and that the devices have consistent characteristics. effect of ideality factor the accuracy of the remote temperature measurementsdepends on the ideality factor (n) of the remote diode (actually a transistor). the max6643/max6644/max6645 are optimized for n = 1.01, which is typical of many dis- crete 2n3904 and 2n3906 transistors. it is also near the ideality factors of many widely available cpus, gpus, and fpgas. however, any time a sense transistor with a differ- ent ideality factor is used, the output data is different. fortunately, the difference is predictable. assume a remote-diode sensor designed for a nominal ideality fac- tor n nominal is used to measure the temperature of a diode with a different ideality factor, n 1 . the measured temperature t m can be corrected using: where temperature is measured in kelvin.as mentioned above, the nominal ideality factor of the max6643/max6644/max6645 is 1.01. as an example, assume the max6643/max6644/max6645 are config- ured with a cpu that has an ideality factor of 1.008. if the diode has no series resistance, the measured data is related to the real temperature as follows: for a real temperature of +60? (333.15k), the mea- sured temperature is 59.33? (332.49k), which is an error of -0.66?. tt n n t 1.01 1.008 t actual m nominal 1 mm = ?? ? ?? ? = ?? ? ?? ? = () . 1 00198 tt n n m actual 1 nominal = ?? ? ?? ? automatic pwm fan-speed controllers with overtemperature output 8 _______________________________________________________________________________________ manufacturer model no. central semiconductor (usa) cmpt3906 rohm semiconductor (usa) sst3906 samsung (korea) kst3906-tf siemens (germany) smbt3906 table 5. remote-sensor transistormanufacturers ot2 ot1 t overt (?) l suffix 006 0 0 high-z 65 017 0 high-z 0 75 high-z high-z 80 high-z 1 85 109 0 1 high-z 95 1 1 100 table 4. setting the overtemperaturethresholds (t overt ) (max6643 and max6644) table 3. configuring the fan_in_ inputs with tachset vdd gnd unconnected tachset fan_in1 fan_in2 fan_in1 fan_in2 fan_in1 fan_in2 max6643 tachometer tachometer do not connect to gnd do not connect to gnd disables fan- failure detection disables fan- failure detection max6644 tachometer tachometer current sense current sense locked rotor locked rotor max6645 tachometer tachometer current sense current sense locked rotor locked rotor high-z = high impedance downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output _______________________________________________________________________________________ 9 max6644 1 2 34 th1 tl2tl1 fanfail tachset dxp2 gnd dxp1 v dd th2ot1 ot2 pwm_out fan_in1 fan_in2 ot 56 7 8 16 15 4.7k 4.7k +v fan (5v or 12v) v dd (+3.0v to +5.5v) +v fan (5v or 12v) 2.0 2.0 4.7k to fanfail alarm 0.1 f 0.1 f 1413 current-sense mode current-sense mode to overtemperaturealarm 1211 10 9 n n max6645 1 fanfail tachset dxp2 gnd dxp1 v dd pwm_out fan_in1 fan_in2 ot 23 4 5 4.7k 4.7k +v fan (5v or 12v) v dd (+3.0v to +5.5v) +v fan (5v or 12v) 4.7k to fanfail alarm 10 tachometer modetachometer mode to overtemperaturealarm 98 7 6 n figure 3. max6644 using two external transistors to measure remote temperatures and control two 2-wire fans. the fan? power-supply current is monitored to detect failure of either fan. connect pin 10 to pin 11 if only one fan is used. figure 4. max6645 using two external transistors to measure remote temperatures and control two 2-wire cooling fans. thefan? power-supply current is monitored to detect failure of either fan. connect fan_in1 to fan_in2 if only one fan is used. downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output 10 ______________________________________________________________________________________ to fanfailalarm max6645 10 n 98 tachometermode tachometer mode to overtemperature alarm 76 fanfailtachset dxp2 gnd dxp1 v dd v dd (+3.0v to +5.5v) +v fan (5v or 12v) 12 3 4 5 pwm_out fan_in1fan_in2 ot 4.7k 4.7k 4.7k figure 5. using the max6645 to monitor two fans downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output ______________________________________________________________________________________ 11 max6643 th1 1615 14 13 12 11 (tachometer mode) (tachometer mode) to overtemperature alarm 109 tl2tl1 fanfail to fanfailalarm to fanfailalarm tachsetfullspd gnd dxp v dd v dd (+3.0v to +5.5v) +v fan (5v or 12v) 12 3 4 5 6 7 8 th2ot1 ot2 pwm_out fan_in1fan_in2 ot 4.7k 4.7k 4.7k nn max6643 th1 1615 14 13 12 11 (tachometer mode)(tachometer mode) to overtemperature alarm 109 tl2tl1 fanfail tachset fullspd gnd dxp v dd v dd (+3.0v to +5.5v) +v fan (5v or 12v) 12 3 4 5 6 7 8 th2ot1 ot2 pwm_out fan_in1fan_in2 ot 4.7k 4.7k 4.7k figure 6. using two max6643s, each controlling a separate fan downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output 12 ______________________________________________________________________________________ effect of series resistance series resistance in a sense diode contributes addition-al errors. for nominal diode currents of 10? and 100?, change in the measured voltage is: since 1? corresponds to 198.6?, series resistance contributes a temperature offset of: assume that the diode being measured has a series resistance of 3 . the series resistance contributes an offset of:the effects of the ideality factor and series resistance are additive. if the diode has an ideality factor of 1.008 and series resistance of 3 , the total offset can be cal- culated by adding error due to series resistance witherror due to ideality factor: 1.36? - 0.66? = 0.7? for a diode temperature of +60.7?.in this example, the effect of the series resistance and the ideality factor partially cancel each other. for best accuracy, the discrete transistor should be a small-signal device with its collector connected to base, and emitter connected to gnd. table 5 lists examples of discrete transistors that are appropriate for use with the max6643/max6644/max6645. the transistor must have a relatively high forward volt- age; otherwise, the adc input voltage range can be vio- lated. the forward voltage at the highest expected temperature must be greater than 0.25v at 10?, and at the lowest expected temperature, the forward voltage must be less than 0.95v at 100?. large power transis- tors must not be used. also, ensure that the base resis- tance is less than 100 . tight specifications for forward current gain (50 < ?<150, for example) indicate that themanufacturer has good process controls and that the devices have consistent v be characteristics. adc noise filtering the integrating adc has inherently good noise rejec-tion, especially of low-frequency signals such as 60hz/120hz power-supply hum. micropower operation places constraints on high-frequency noise rejection. lay out the pcb carefully with proper external noise fil- tering for high-accuracy remote measurements in elec- trically noisy environments. filter high-frequency electromagnetic interference (emi) at the dxp pins with an external 2200pf capaci- tor connected between dxp, dxp1, or dxp2 and ground. this capacitor can be increased to about 3300pf (max), including cable capacitance. a capaci- tance higher than 3300pf introduces errors due to the rise time of the switched-current source. twisted pairs and shielded cables for remote-sensor distances longer than 8in, or in par-ticularly noisy environments, a twisted pair is recom- mended. its practical length is 6ft to 12ft (typ) before noise becomes a problem, as tested in a noisy electron- ics laboratory. for longer distances, the best solution is a shielded twisted pair like that used for audio micro- phones. for example, belden 8451 works well for dis- tances up to 100ft in a noisy environment. connect the twisted pair to dxp and gnd and the shield to ground, and leave the shield? remote end unterminated. excess capacitance at dxp limits practical remote-sensor dis- tances (see the typical operating characteristics ). for very long cable runs, the cable? parasitic capaci-tance often provides noise filtering, so the recommend- ed 2200pf capacitor can often be removed or reduced in value. cable resistance also affects remote-sensor accuracy. a 1 series resistance introduces about +1/2? error. pcb layout checklist 1) place the max6643/max6644/max6645 as close as practical to the remote diode. in a noisy environment,such as a computer motherboard, this distance can be 4in to 8in or more, as long as the worst noise sources (such as crts, clock generators, memory buses, and isa/pci buses) are avoided. 2) do not route the dxp lines next to the deflection coils of a crt. also, do not route the traces across a fastmemory bus, which can easily introduce +30? error, even with good filtering. otherwise, most noise sources are fairly benign. 3 c c = . . 0 453 1 36 90 198 6 0 453 = v v c c . . v m = () = raa a r ss 100 10 90 downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output ______________________________________________________________________________________ 13 3) route the dxp and gnd traces parallel and close to each other, away from any high-voltage traces suchas +12vdc. avoid leakage currents from pcb conta- mination. a 20m leakage path from dxp to ground causes approximately +1? error. 4) route as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 5) when introducing a thermocouple, make sure that both the dxp and the gnd paths have matchingthermocouples. in general, pcb-induced thermocou- ples are not a serious problem. a copper solder ther- mocouple exhibits 3?/?, and it takes approximately 200? of voltage error at dxp/gnd to cause a +1? measurement error, so most parasitic thermocouple errors are swamped out. 6) use wide traces. narrow traces are more inductive and tend to pick up radiated noise. the 10-mil widthsand spacings are recommended, but are not absolutely necessary (as they offer only a minor improvement in leakage and noise), but use them where practical. 7) placing an electrically clean copper ground plane between the dxp traces and traces carrying high-frequency noise signals helps reduce emi. chip information transistor count: 12,518process: bicmos downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output 14 ______________________________________________________________________________________ part package-pins startup delay (s) spin-up time (s) start duty cycle (%) minimum duty cycle (%) channels tl ( c) th ( c) ot ( c) fullspd polarity fan_in1fan_in2 max6643lbfaee qsop-16 0.5 8 40 40 remote, local 15 to 55 20 to 60 60 to 100 fullspd tach/off tach/off max6643lbbaee qsop-16 0.5 8 30 30 remote, local 15 to 55 20 to 60 60 to 100 fullspd tach/off tach/off MAX6644LBAAEE qsop-16 0.5 8 30 0 remote, remote 15 to 55 20 to 60 60 to 100 locked r otor /tach/ cur r ent sense locked r otor /tach/ cur r ent sense m ax 6645 abfau b ?ax-10 0.5 8 40 40 remote, remote 45 50 75 locked r otor /tach/ cur r ent sense locked r otor /tach/ cur r ent sense selector guide pin configurations 1615 14 13 12 11 10 9 12 34 5 6 7 8 th1 v dd th2ot1 ot2 pwm_out fan_in1 fan_in2 ot top view max6643 qsop tl2tl1 fullspd (fullspd) fanfail tachset gnd dxp 1615 14 13 12 11 10 9 12 34 5 6 7 8 th1 v dd th2ot1 ot2 pwm_out fan_in1 fan_in2 ot max6644 qsop tl2tl1 dxp2 fanfail tachset gnd dxp1 1 23 4 5 10 98 7 6 v dd pwm_outfan_in1 fan_in2 gnd dxp2 tachset fanfail max6645 max ot dxp1 () are for max6643_a only. downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output ______________________________________________________________________________________ 15 max6643max6644 max6645 dxp1/(dxp) dxp2 temperature sensor temperature logic pwm generator fan-fail detection duty cycle analog sense tachometer locked rotor in analog sense tachometer locked rotor in ot th tl threshold selection fullspd/(fullspd) pwm_outfan_in1 fan_in2 fanfail tachset ot1 ot2 th1 th2 tl1 tl2 () are for max6643 only. block diagram to fanfailalarm max6643 th1 1615 14 13 12 11 (tachometer mode)(tachometer mode) to overtemperature alarm 109 tl2tl1 fanfail tachset fullspd gnd dxp v dd v dd (+3.0v to +5.5v) +v fan (5v or 12v) 12 3 4 5 6 7 8 th2ot1 ot2 pwm_out fan_in1fan_in2 ot 4.7k 4.7k 4.7k n typical operating circuit downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output 16 ______________________________________________________________________________________ package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) qsop.eps f 1 1 21-0055 package outline, qsop .150", .025" lead pitch downloaded from: http:///
max6643/max6644/max6645 automatic pwm fan-speed controllers with overtemperature output 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. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 17 2007 maxim integrated products is a registered trademark of maxim integrated products, inc. package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) 10lumax.eps package outline, 10l umax/usop 1 1 21-0061 rev. document control no. approval proprietary information title: top view front view 1 0.498 ref 0.0196 ref s 6 side view bottom view 0 0 6 0.037 ref 0.0078 max 0.006 0.043 0.118 0.120 0.199 0.0275 0.118 0.0106 0.120 0.0197 bsc inches 1 10 l1 0.0035 0.007 e c b 0.187 0.0157 0.114 h l e2 dim 0.116 0.114 0.116 0.002 d2 e1 a1 d1 min - a 0.940 ref 0.500 bsc 0.090 0.177 4.75 2.89 0.40 0.200 0.270 5.05 0.70 3.00 millimeters 0.05 2.89 2.95 2.95 - min 3.00 3.05 0.15 3.05 max 1.10 10 0.60.1 0.60.1 0.500.1 h 4x s e d2 d1 b a2 a e2 e1 l l1 c gage plane a2 0.030 0.037 0.75 0.95 a1 revision history pages changed at rev 2: 1, 2, 4?, 11?5, 17 downloaded from: http:///

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