View MIC502YM_3120499.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

mic502 fan management ic micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.micrel.com november 2006 1 m9999-112206 general description the mic502 is a thermal and fan management ic which supports the features for nlx/atx power supplies and other control applications. fan speed is determined by an external temperature sensor, typically a thermistor-resistor divider, and (option- ally) a second signal, such as the nlx ?fanc? signal. the mic502 produces a low-frequency pulse-width modulated output for driving an external motor drive transistor. low- frequency pwm speed control allows operation of standard brushless dc fans at low duty cycle for reduced acoustic noise and permits th e use of a very small power transistor. the pwm time base is determined by an external capacitor. an open-collector overtemperat ure fault output is asserted if the primary control inpu t is driven above the normal control range. the mic502 features a low-power sleep mode with a user- determined threshold. sleep mode completely turns off the fan and occurs when the system is asleep or off (both control inputs very low). a complete shutdown or reset can also be initiated by extern al circuitry as desired. the mic502 is available as 8-pin plastic dip and soic packages in the ?40c to +8 5c industrial temperature range. data sheets and support doc umentation can be found on micrel?s web site at www.micrel.com. features ? temperature-proportional fan speed control ? low-cost, efficient pwm fan drive ? 4.5v to 13.2v ic supply range ? controls any voltage fan ? overtemperature detection with fault output ? integrated fan startup timer ? automatic user-specified sleep mode ? supports low-cost ntc/ptc thermistors ? 8-pin dip and soic packages applications ? nlx and atx power supplies ? personal computers ? file servers ? telecom and networking hardware ? printers, copiers, and office equipment ? instrumentation ? uninterruptible power supplies ? power amplifiers ___________________________________________________________________________________________________________ typical application vt1 cf vslp gnd vdd out otf vt2 1 2 3 4 8 7 6 5 r1 t1 r3 r4 c f r2 12v r base overtemperature fault output mic502 secondary fan-contro l input fan q1
micrel, inc. mic502 november 2006 2 m9999-112206 ordering information part number temperature range package lead finish mic502bn ?40 to +85c 8-pin plastic dip standard mic502yn ?40 to +85c 8-pin plastic dip pb-free mic502bm ?40 to +85c 8-pin soic standard MIC502YM ?40 to +85c 8-pin soic pb-free pin configuration 1 2 3 4 8 7 6 5 vdd out otf vt2 vt1 cf vslp gnd 8-pin soic (m) 8-pin dip (n) pin description pin number pin name pin function 1 vt1 thermistor 1 (input): analog input of approximately 30% to 70% of v dd produces active duty cycle of 0% to 100% at driver output (out). connect to external thermistor network (or other tem perature sensor). pull low for shutdown. 2 cf pwm timing capacitor (external component): positive terminal for the pwm triangle-wave generator timing capacitor. the recommended c f is 0.1f for 30hz pwm operation. 3 vslp sleep threshold (input): the voltage on this pin is compared to vt1 and vt2. when v t1 < v slp and v t2 < v slp the mic502 enters sleep mode until v t1 orv t2 rises above v wake . (v wake = v slp + v hyst ). grounding v slp disables the sleep- mode function. 4 gnd ground. 5 vt2 thermistor 2 (input): analog input of approximately 30% to 70% of v dd produces active duty cycle of 0% to 100% at driver output (out). connect to motherboard fan control signal or second temperature sensor. 6 /otf overtemperature fault (output): open -collector output (active low).indicates overtemperature fault condition (v t1 > v ot ) when active. 7 out driver output: asymmetrical-drive active-high complimentary pwm output. typically connect to base of external npn motor control transistor. 8 vdd power supply (input): ic supply input; may be independent of fan power supply.
micrel, inc. mic502 november 2006 3 m9999-112206 absolute maximum ratings (1) supply voltage (v dd )....................................................+14v output sink current (i out(sink) ) .....................................10ma output source current (i out(source) ) ..............................25ma input voltage (any pin) .......................... ?0.3v to v dd +0.3v junction temperature (t j ) ....................................... +125c lead temperature (solde ring, 5 se c.) ........................ 260c storage temperature (t a ).........................?65c to +150c esd rating (3) operating ratings (2) supply voltage (v dd )....................................... +4v to 13.2v sleep voltage (v slp ).......................................... gnd to v dd temperature range (t a )............................. ?40c to +85c power dissipation at 25c soic ..................................................................800m w dip .....................................................................740m w derating factors soic ..............................................................8.3mw/c plastic dip .....................................................7.7mw/c electrical characteristics 4.5v v dd 13.2v, note 4 ; t a = 25c, bold values indicate ?40c t a < +85c, unless noted. symbol parameter condition min typ max units i dd supply current, operating v slp = gnd, otf, out = open, c f = 0.1f, v t1 = v t2 = 0.7 v dd 1.5 ma i dd(slp) supply current, sleep v t1 = gnd, v slp , otf, out = open, c f = 0.1f 500 a driver output t r output rise time, note 5 i oh = 10ma 50 s t f output fall time, note 5 i ol = 1ma 50 s i ol output sink current v ol = 0.5v 0.9 ma 4.5v v dd 5.5v, v oh = 2.4v 10 ma i oh output source current 10.8v v dd 13.2v, v oh = 3.2v 10 ma i os sleep-mode output leakage v out = 0v 1 a thermistor and sleep inputs v pwm(max) 100% pwm duty cycle input voltage 67 70 73 %v dd v pwm(span) v pwm(max) ? v pwm(min) 37 40 43 %v dd v hyst sleep comparator hysteresis 8 11 14 %v dd v il vt1 shutdown threshold 0.7 v v ih vt1 startup threshold 1.1 v v ot vt1 overtemperature fault threshold note 6 74 77 80 %v dd i vt , i vslp vt1, vt2, vslp input current ?2.5 1 a t reset reset setup time minimum time v t1 < v il , to guarantee reset, note 5 30 s oscillator 4.5v v dd 5.5v, c f = 0.1f 24 27 30 hz f oscillator frequency, note 7 10.8v v dd 13.2v, c f = 0.1f 27 30 33 hz f min , f max oscillator frequency range note 7 15 90 hz t startup startup interval 64/f s
micrel, inc. mic502 november 2006 4 m9999-112206 symbol parameter condition min typ max units overtemperature fault output v ol active (low) output voltage i ol = 2ma 0.3 v i oh off-state leakage v /otf = v dd 1 a notes: 1. exceeding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. devices are esd sensitive. handling precautions recommended. 4. part is functional over this v dd range; however, it is charac terized for operation at 4.5v v dd 5.5v and 10.8v v dd 13.2v ranges. these ranges correspond to nominal v dd of 5v and 12v, respectively. 5. guaranteed by design. 6. v ot is guaranteed by design to always be higher than v pwm(max) . 7. logic time base and pwm frequency. for other values of c f , f(hz) = 30hz c f 0.1 , where c is in f. timing diagrams v oh v ol 50% 80% 40% 0% 100% 40% 70% t startup t pwm output duty cycl e abcde f g 0.7v dd 0.3v dd 0.3v dd v t1 v t2 v slp 100% 0% 30% 70% 80% 50% 40% 40% input signal range v ot v ih v il 0v v oh v ol v out v otf 0v 0v figure 1. typical system behavior note a. output duty-cycle is initially determined by v t1 , as it is greater than v t2 . note b. pwm duty-cycle follows v t1 as it increases. note c. v t1 drops below v t2 . v t2 now determines the output duty-cycle. note d. the pwm duty-cycle follows v t2 as it increases. note e. both v t1 and v t2 decrease below v slp but above vil. the device enters sleep mode. note f. the pwm ?wakes up? because one of the control inputs (v t1 in this case) has risen above v wake . the startup timer is triggered, forcing out high for 64 clock periods. (v wake = v slp + v hyst . see ?electrical characteristics?). note g. following the startup interval, the pwm duty-cycle is the higher of v t1 and v t2 .
micrel, inc. mic502 november 2006 5 m9999-112206 v oh v ol 40% 60% 30% 0% 100% t startup t pwm output duty cycl e hi jk m n l 0.7v dd 0.3v dd 0.3v dd v t1 v t2 v slp 100% 0% 20% 60% 40% 30% pwm range v ot v ih v il 0v v oh v ol v out v otf o 100% v dd 0v v dd 0v 0v figure 2. mic502 typical power-up system behavior note h. at power-on, the startup timer forces out on fo r 64 pwm cycles of the internal timebase (t pwm ). this insures that the fan will start from a dead stop. note i. the pwm duty-cycle follows the higher of v t1 and v t2 , in the case, v t1 . note j. the pwm duty-cycle follows v t1 as it increases. note k. pwm duty-cycle is 100% (out constantly on) anytime v t1 > v pwm(max) . note l. /otf is asserted anytime v t1 > v ot . (the fan continues to run at 100% duty-cycle). note m. /otf is deasserted when v t1 falls below v ot ; duty-cycle once again follows v t1 . note n. duty-cycle follows v t1 until v t1 < v t2 , at which time v t2 becomes the controlling input signal. note that v t1 is below v slp but above v ih ; so normal operation continues. (both v t1 and v t2 must be below v slp to active sleep mode). note o. all functions cease when v t1 < v il ; this occurs regardless of the state of v t2 .
micrel, inc. mic502 november 2006 6 m9999-112206 typical characteristics 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 2 4 6 8 101214 i d d ) a m ( v dd (v) supply current vs. supply voltage 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 02468101214 v l o ) v ( v dd (v) v ol vs. supply voltage i ol = 0.9ma 0 5 10 15 20 25 30 35 02468101214 v l o ) v m ( v dd (v) v ol vs. supply voltage i ol = 100a 0 0.05 0.10 0.15 0.20 0.25 -40-20 0 20406080100 v l o ) v ( temperature ( c) v ol vs. temperature v dd =12v v dd = 5v 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -40-20 0 20406080100 i d d ) a m ( temperature ( c) supply current vs. temperature v dd = 12v v dd = 5v 0 0.05 0.1 0.15 0.2 0.25 0.3 -40-20 0 2040608010 0 d d i p e e l s ) a m ( temperature ( c) idd sleep vs . temperature v dd = 12v v dd = 5v 0 0.5 1 1.5 2 2.5 3 3.5 4 02468101214 v h o ) v ( v dd (v) v oh vs. supply voltage i oh = 10ma 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 02468101214 v h o ) v ( v dd (v) v oh vs. supply voltage i oh = 100a 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 -40-20 0 2040608010 0 v h o ) v ( temperature ( c) v oh vs. temperature v dd = 12v v dd = 5v
micrel, inc. mic502 november 2006 7 m9999-112206 typical characteristics (cont.) 0 1 2 3 4 5 6 7 8 9 -40 -20 0 20 40 60 80 100 v ) x a m ( m w p ) v ( temperature ( c) v pwm(max) vs. temperature v dd =12v v dd = 5v 0 1 2 3 4 5 6 7 8 9 10 0 2 4 6 8 101214 v t o ) v ( v dd (v) v ot vs. supply voltage 1 10 100 1000 3000 0.001 0.01 0.1 1 ) z h ( y c n e u q e r f capacitance ( f) pwm frequency vs . timing capacitor value 0 0.2 0.4 0.6 0.8 1 1.2 -40 -20 0 20 40 60 80 100 f m w p ) d e z i l a m r o n ( temperature ( c) pwm frequency (normalized) vs. temperature v dd = 12v v dd = 5v 0 1 2 3 4 5 6 7 8 9 10 -40 -20 0 20 40 60 80 100 v t o ) v ( temperature ( c) v ot vs. temperature v dd = 12v v dd = 5v
micrel, inc. mic502 november 2006 8 m9999-112206 functional diagram oscillator start-up timer clk reset out vt2 vt1 cf otf out driver gnd vslp power-on reset enable sleep control vdd overtemperature reset sleep bias v il pwm 8 3 5 6 7 4 2 1
micrel, inc. mic502 november 2006 9 m9999-112206 functional description oscillator a capacitor connected to cf determines the frequency of the internal time base wh ich drives the state-machine logic and determines the pwm frequency. this operating frequency will be typically 30hz to 60hz. (c f = 0.1f for 30hz.) pulse-width modulator a triangle-wave generator and threshold detector comprise the internal pulse-width modulator (pwm). the pwm?s output duty-cycle is determined by the higher of v t1 or v t2 . a typical voltage range of 30% to 70% of v dd applied to the v t1 and v t2 pins corresponds to 0% to 100% duty-cycle. since at least one of the control voltage inputs is generally from a thermistor-resistor divider connected to v dd , the pwm out-put duty cycle will not be affected by cha nges in the supply voltage. driver output out is a complementary push-pull digital output with asymmetric drive (approximately 10ma source, 1ma sink, see ?electrical characteristics?). it is optimized for directly driving an npn transistor switch in the fan?s ground-return. see ?applications information? for circuit details. shutdown/reset internal circuitry automatically performs a reset of the mic502 when power is applied. the mic502 may be shut down at anytime by forcing v t1 below its v il threshold. this is typically accomplished by connecting the v t1 pin to open-drain or open-collector logic and results in an immediate and asynchronous shutdown of the mic502. the out and /o tf pins will float while v t1 is below v il . if v t1 then rises above v ih , a device reset occurs. reset is equivalent to a power-up co ndition: the state of /otf is cleared, a startup interval is triggered, and normal fan operation begins. startup interval any time the fan is started from the off state (power-on or coming out of sleep mode or shutdown mode), the pwm output is automatically forced high for a startup interval of 64 t pwm . once the startup interval is complete, pwm operation will commence and the duty- cycle of the output will be determined by the higher of v t1 or v t2 . overtemperature fault output /otf is an active-low, open-collector logic output. an over-temperature condition will ca use /otf to be asserted. an overtemperature condition is determined by v t1 exceeding the normal operating range of 30% to 70% of v dd by > 7% of v dd . note that v ot is guaranteed by design to always be higher than v pwm(max) . sleep mode when v t1 and v t2 fall below v slp , the system is deemed capable of operating without fan cooling and the mic502 enters sleep mode and discont inues fan operation. the threshold where the mic502 enters sleep mode is deter- mined by v slp . connecting the v slp pin to ground disables sleep mode. once in sleep mode, all device functions cease (/otf in- active, pwm output off) unless v t1 or v t2 rise above v wake . (v wake = v slp + v hyst ). v hyst is a fixed amount of hysteresis added to the sleep comparator which prevents erratic operation around the v slp operating point. the result is stable and predictable thermostatic action: whenever possible the fan is shut down to reduce energy consumption and acoustic noise, but will always be activated if the syst em temperature rises. if the device powers-up or exits its reset state, the fan will not start unless v t1 or v t2 rises above v wake . system operation power up ? a complete reset occurs when power is applied. ? out is off (low) and /otf is inactive (high/floating). ? if v t1 < v il , the mic502 remains in shutdown. ? the startup interval begins. out will be on (high) for 64 clock cycles (64 t pwm ). ? following the startup interval, normal operation begins. reset startup timer; deassert /otf; out off (low) . v t1 >v ot ? power on v t1 v ot normal operation yes yes figure 3. power-up behavior
micrel, inc. mic502 november 2006 10 m9999-112206 normal operation normal operation consists of the pwm operating to control the speed of the fan according to v t1 and v t2 . exceptions to this otherwise indefinite behavior can be caused by any of three conditions: v t1 exceeding v ot , an overtemperature condition; v t1 being pulled below v il initiating a device shutdown and reset; or both v t1 and v t2 falling below v slp , activating sleep mode. each of these exceptions is treated as follows: overtemp? v t1 >v ot ? normal operation v t1 and v t2 v ot reset? v t1 v ot ) overtemperature detection is essentially independent of other operations ? the pwm continues its normal behavior; with v t1 > v pwm(max) , the output duty-cycle will be 100%. if v t1 falls below v ot , the overtemperature condition is cleared and /otf is no longer asserted. it is assum ed that in most systems, the /otf output will initiate power supply shutdown. ? shutdown/reset: if v t1 is driven below v il an immediate, asynchronous shutdown occurs. while in shutdown mode, out is off (low), and /otf is unconditionally inactive (high/floating). if v t1 subsequently rises above v ih , a device reset will occur. reset is indistinguishable from a power-up condition. the state of /o tf is cleared, a startup interval is triggered, and normal fan operation begins. ? sleep: if v t1 and v t2 fall below v slp , the device enters sleep mode. all internal functions cease unless v t1 or v t2 rise above v wake . (v wake = v slp + v hyst ). the /otf output is unconditionally inactive (high/floating) and the pwm is disabled during sleep (out will float). sleep mode during normal operation, if v t1 and v t2 fall below v slp , the device will go into sleep mode and fan operation will stop. the mic502 will exit sleep mode when v t1 or v t2 rise above v slp by the hysteresis voltage, v hyst . when this occurs, normal operation will resume. the resumption of normal operation upon exiting sleep is indistinguishable from a power-on reset. (see ?sleep: normal operation,? above.) disable pwm reset released v t1 >v ih ? sleep reset initiate d v t1 v slp +v hyst ? power on no no no yes figure 5. sleep-mode behavior
micrel, inc. mic502 november 2006 11 m9999-112206 application information the typical application draw ing on page 1 illustrates a typical application circuit for the mic502. interfacing the mic502 with a system consists of the following steps: 1. selecting a temperature sensor 2. interfacing the temperature sensor to the v t1 input 3. selecting a fan-drive transistor, and base-drive current limit resistor 4. deciding what to do with the secondary fan- control input 5. making use of the overtemperature fault output temperature sensor selection temperature sensor t1 is a negative temperature coefficient (ntc) thermi stor. the mic502 can be interfaced with either a negative or positive tempco thermistor; however, a negat ive temperature coefficient thermistor typically costs less than its equivalent positive tempco counterpart. while a variety of thermistors can be used in this application, the following paragraphs reveal that those with an r25 rating (resistance at 25c) of from about 50k ? to 100k ? lend themselves nicely to an interface network that requires only a modest current drain. keeping the thermistor bias current low not only indicates prudent design; it al so prevents self-heating of the sensor from becoming an additional design consideration. it is assumed that the thermistor will be located within the system power supply, which most likely also houses the speed-controlled fan. temperature sensor interface as shown by the electrical characteristics table, the working voltage for input v t1 is specified as a percentage of v dd . this conveniently frees the designer from having to be concerned with interactions resulting from variations in the supply voltage. by design, the operating range of v t1 is from about 30%of v dd to about 70% of v dd . v pwm(min) = v pwm(min) ? v pwm(span) when v t1 = v pwm(max) 0.7v dd , a 100% duty-cycle motor-drive signal is gene rated. conversely, when v t1 = v pwm(min) 0.3v dd , the motor-drive signal has a 0% duty cycle. resistor voltage divider r1 || t1, r2 in the typical application diagram is designed to preset v t1 to a value of v pwm that corresponds to the slowest desired fan speed when the resistance of thermistor t1 is at its highest (cold) value. as tem perature rises the resistance of t1 decreases and v t1 increases because of the parallel connection of r1 and t1. since v t1 = v pwm(min) represents a stopped fan (0% duty- cycle drive), and since it is foreseen that at least some cooling will almost always be required, the lowest voltage applied to the v t1 input will normally be somewhat higher than 0.3v dd (or >v pwm(min) ). it is assumed that the system w ill be in sleep mode rather than operate the fan at a ve ry low duty cycle (<25%). operation at very low duty cycl e results in relatively little airflow. sleep mode should be used to reduce acoustic noise when the system is cool. for a given minimum desired fan speed, a corresponding v t1(min) can be determined via the following observation: since v pwm(max) = 70% of v dd 100% rpm and v pwm(min) = 30% of v dd 0% rpm then v pwm(span) = 40% of v dd 100% rpm range . figure 6 shows the following linear relationship between the voltage applied to the v t1 input, motor drive duty cycle, and approximate motor speed. since v t1 = 0.7v dd 100% pwm then v t1 = 0.6v dd 75% pwm and v t1 = 0.5v dd 50% pwm and v t1 = 0.4v dd 25% pwm in addition to the r25 thermistor rating, sometimes a datasheet will provide the rati o of r25/r50 (resistance at 25c divided by resistance at 50c) is given. sometimes this is given as an r0/r50 ratio. other datasheet contents either specify or help the user determine device resistance at arbitrary te mperatures. the thermistor interface to the mic502 usually consists of the thermistor and two resistors. 0 20 40 60 80 100 0 20406080100 duty cycle (%) v t1 /supply voltage (%) figure 6. control voltage vs. fan speed
micrel, inc. mic502 november 2006 12 m9999-112206 design example the thermistor-resistor interface network is shown in the typical application drawing. the following example describes the design proce ss: a thermistor datasheet specifies a thermistor that is a candidate for this design as having an r25 resistance of 100k ? . the datasheet also supports calculation of resistance at arbitrary tem- peratures, and it was discovered the candidate thermistor has a resistance of 13.6k at 70c (r70). accuracy is more important at the higher temperature end of the operating range (70c) than the lower end because we wish the overtemperature fault output (/otf) to be reasonably accurate ? it may be critical to operating a power supply crow bar or other shutdown mechanism, for example. the lower temperature end of the range is less important because it simply establishes minimum fan speed, which is when less cooling is required. referring to the ?typical application,? the following approach can be used to design the required thermistor interface network: let r1 = r t1 = 13.6k (at 70c) and v t = 0.7v dd (70% of vdd) since () r2 r1 || r r2 v v t1 dd t + = () r2 r r2 0.7 t1 + = 0.7r t1 + 0.7r2 = r2 0.7r t1 = 0.3r2 and r2 = 2.33r t1 = 2.33 13.6k = 31.7k 33k let?s continue by determi ning what the temperature- proportional voltage is at 25c. let r1 = and r t1 = 100k (at 25c). from () r2 r r2 v v t1 dd t + = () 33k 100k 33k v v dd t + = v t = 0.248v dd recalling from above discussion that the desired v t for 25c should be about 40% of v dd , the above value of 24.8% is far too low. this would produce a voltage that would stop the fan (recall from the above that this occurs when v t is about 30% of v dd . to choose an appropriate value for r1 we need to learn what the parallel combination of r t1 and r1 should beat 25c: again () r2 r1 || r r2 v v t1 dd t + = () r2 r1 || r r2 0.4 t1 + = 0.4(r t1 || r1) + 0.4r2 = r2 0.4(r t1 || r1) = 0.6r2 and r t1 || r1 = 1.5r2 = 1.5 33k = 49.5k since r t1 = 100k and r t1 || r1 = 49.5k 50k let r1 = 100k while that solves the low te mperature end of the range, there is a small effect on t he other end of the scale. the new value of v t for 70c is 0.734, or about 73% of v dd . this represents only a 3% shift from the design goal of 70% of v dd . in summary, r1 = 100k, and r2 = 33k. the candidate thermistor used in this design example is the rl2010-54.1k-138-d1, manufactured by keystone thermometrics. the r25 resistance (100k ? ) of the chosen thermistor is probably on the high side of the range of potential thermistor resistances. the result is a moderately high- impedance network for connecting to the v t1 and/or v t2 input(s). because these input s can have up to 1a of leakage current, care must be taken if the input network impedance becomes higher t han the example. leakage current and resistor accuracy could require consideration in such designs. note that the v slp input has this same leakage current specification. secondary fan-control input the above discussions also apply to the secondary fan- control input, v t2 , pin 5. it is possible that a second thermistor, mounted at another temperature-critical location outside the power supply, may be appropriate. there is also the possibilit y of accommodat ing the nlx ?fanc? signal via this input. if a second thermistor is the desired solution, the v t2 input may be treated exactly like the v t1 input. the above discussions then apply directly. if, however, the nlx fanc signal is to be
micrel, inc. mic502 november 2006 13 m9999-112206 incorporated into the des ign then the operating voltage (v dd = 5v vs. v dd = 12v) becomes a concern. the fanc signal is derived from a 12v supply and is specified to swing at least to 10.5v. a minimum implementation of the fanc signal would provi de the capability of asserting full-speed operation of the f an; this is the case when 10.5v fanc 12v. this fanc signal can be applied directly to the v t2 input of the mic502, but only when its v dd is 12v. if this signal is required when the mic502 v dd = 5v a resistor divider is necessary to reduce this input voltage so it doe s not exceed the mic502 v dd voltage. a good number is 4v (80%v dd ). because of input leakage considerations, the impedance of the resistive divider should be kept at 100k ? . a series resistor of 120k ? driven by the fanc signal and a 100k ? shunt resistor to ground make a good divider for driving the v t2 input. transistor and base-drive resistor selection the out motor-drive output, pin 7, is intended for driving a medium-power device, such as an npn transistor. a rather ubiquitous transistor, the 2n2222a, is capable of switching up to about 400ma. it is also available as the pn2222a in a plastic to-92 package. since 400ma is about the maximum current for most popular computer power supply fans (with many drawing substantially less current) and since the mic502 provides a minimum of 10ma output current, the pn2222a, with its minimum of 40, is the chosen motor- drive transistor. the design consists solely of choosing the value r base in figures 7 and 8. to minimize on-chip power dissipation in the mic502, the value of r base should be determined by the power supply voltage. the electrical characteristics table specif ies a minimum output current of 10ma. however, differe nt output voltage drops (v dd ? v out ) exist for 5v vs.12v operation. the value r base should be as high as possible for a given required transistor base-drive current in order to reduce on-chip power dissipation. referring to the ?typical application? and to the ?electrical characteristics? table, the value for r base is calculated as follows. for v dd = 5v systems, i oh of out (pin 7) is guaranteed to be a minimum of 10ma with a v oh of 2.4v. r base then equals (2.4v ? v be ) 10ma = 170 ? . for v dd = 12v systems, r base = (3.4 ? 0.7) 0.01 = 250 ? . overtemperature fault output the /otf output, pin 6, is an open-collector npn output. it is compatible with cmos and ttl logic and is intended for alerting a system about an overtemperature condition or triggering a power supply crowbar circuit. if v dd for the mic502 is 5v the output should not be pulled to a higher voltage. this output can sink up to 2ma and remain compatible with the ttl logic-low level. timing capacitors vs. pwm frequency the recommended c f (see first page) is 0.1f for operation at a pwm frequency of 30hz. this frequency is factory trimmed within 3hz using a 0.1% accurate capacitor. if it is desired to operate at a different frequency, the new value for c f is calculated as follows: f 3 c = , where c is in f and f is in hz the composition, voltage rati ng, esr, etc., parameters of the capacitor are not critic al. however, if tight control of frequency vs. temperature is an issue, the temperature coefficient may become a consideration. vt1 cf vslp gnd vdd out otf vt2 1 2 3 4 8 7 6 5 r1 100k t1 r3 56k r4 56k c f r2 33k 5v r base overtemperature fault output mic502 nlx fanc signal input yate loon yd80sm-12 or similar fan q1 0.1f 180 100k 47k keystone thermonics rl2010-54.1k-138-d1 or similar 120k 12v figure 7. typical 5v v dd application circuit vt1 cf vslp gnd vdd out otf vt2 1 2 3 4 8 7 6 5 r1 100k t1 r3 56k r4 56k c f r2 33k 12v r base overtemperature fault output mic502 nlx fanc signal input yate loon yd80sm-12 or similar fan q1 0.1f 280 5v 4.7k 47k keystone thermonics rl2010-54.1k-138-d1 or similar figure 8. typical 12v v dd application circuit
micrel, inc. mic502 november 2006 14 m9999-112206 package information 4 5 0?8 0.244 (6.20) 0.228 (5.79) 0.197 (5.0) 0.189 (4.8) se ating plane 0.026 (0.65) max ) 0.010 (0.25) 0.007 (0.18) 0.064 (1.63) 0.045 (1.14) 0.0098 (0.249) 0.0040 (0.102) 0.020 (0.51) 0.013 (0.33) 0.157 (3.99) 0.150 (3.81) 0.050 (1.27) typ pin 1 dimensions: inches (mm) 0.050 (1.27) 0.016 (0.40) 8-pin soic (m) 0.380 (9.65) 0.370 (9.40) 0.135 (3.43) 0.125 (3.18) pin 1 dimensions: inch (mm) 0.018 (0.57) 0.100 (2.54) 0.013 (0.330) 0.010 (0.254) 0.300 (7.62) 0.255 (6.48) 0.245 (6.22) 0.380 (9.65) 0.320 (8.13) 0.0375 (0.952) 0.130 (3.30) 8-pin plastic dip (n)
micrel, inc. mic502 november 2006 15 m9999-112206 micrel, inc. 2180 fortune drive san jose, ca 95131 usa tel +1 (408) 944-0800 fax +1 (408) 474-1000 web http://www.micrel.com the information furnished by micrel in this data sheet is believ ed to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change ci rcuitry and specifications at any time without notification to the customer. micrel products are not designed or authoriz ed for use as components in life support appl iances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. life suppo rt devices or systems are devices or systems that (a) are in tended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significan t injury to the user. a purchaser?s use or sale of micrel products for use in life support appl iances, devices or systems is a purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2003 micrel, incorporated.

▲Up To Search▲

Price & Availability of MIC502YM

	To Download MIC502YM Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .