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general description the MAX6660 is a remote temperature sensor and fan- speed regulator that provides a complete fan-control solution. the remote temperature sensor is typically a common-collector pnp, such as a substrate pnp of a microprocessor, or a diode-connected transistor, typi- cally a low-cost, easily mounted 2n3904 npn type or 2n3906 pnp type. the device also incorporates a closed-loop fan con- troller that regulates fan speed with tachometer feed- back. the MAX6660 compares temperature data to a fan threshold temperature and gain setting, both pro- grammed over the smbus by the user. the result is automatic fan control that is proportional to the remote- junction temperature. the temperature feedback loop can be broken at any time for system control over the speed of the fan. fan speed is voltage controlled as opposed to pwm controlled, greatly reducing acoustic noise and maxi- mizing fan reliability. an on-chip power device drives fans rated up to 250ma. temperature data is updated every 0.25s and is read- able at any time over the smbus interface. the MAX6660 is accurate to 1? (max) when the remote junction is between +60? to +100?. data is formatted as a 10-bit + sign word with 0.125? resolution. the MAX6660 is specified for -40? to +125? and is available in a 16-pin qsop package. applications pc notebooks telecom systems industrial control systems servers workstations features integrated thermal sensing and fan-regulation solution programmable fan threshold temperature programmable temperature range for full-scale fan speed accurate closed-loop fan-speed regulation on-chip power device drives fans rated up to 250ma programmable under/overtemperature alarms smbus 2-wire serial interface with timeout (cannot ?ock up?the smbus) supports smbus alert response acpi compatible, including overt system shutdown function ?? (+60? to +100?) thermal-sensing accuracy MAX6660evkit available MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface ________________________________________________________________ maxim integrated products 1 part temp. range pin-package MAX6660aee -40 c to +125 c 16 qsop 19-2225; rev 0; 10/01 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ordering information pin configuration appears at end of data sheet. smbus is a trademark of intel corp. 1 f 5k ? fan +12v 2200pf pentium smbclk smbdata alert overt clock data interupt to p to system shutdown vfan add1 add0 pgnd 0.1 f +3v to +5.5v 50 ? v cc stby tach in fan dxp dxn agnd 10k ? each MAX6660 typical operating circuit
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +3v to +5.5v, v vfan = +12v, t a = -40 c to +125 c, unless otherwise specified. typical values are at v cc = +3.3v and t a = +25 c.) (note 1) 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 referenced to gnd v cc , add0, add1, smbdata, smbclk, alert , overt ...................................-0.3v to +6v v fan , tach in, fan .............................................-0.3v to +16v dxp, gain..................................................-0.3v to (v cc + 0.3v) dxn.............................................................................-0.3v to 1v smbdata, alert , overt current ...................-1ma to +50ma dxn current ......................................................................1ma fan out current ..............................................................500ma esd protection (human body model)................................2000v continuous power dissipation (t a = +70 c) 16-pin qsop (derate 8.3mw/ c above +70 c)..........667mw operating temperature range ........................ -40 c to +125 c junction temperature .....................................................+150 c storage temperature range .............................-65 c to +150 c lead temperature (soldering, 10s) .................................+300 c parameter sym b o l conditions min typ max units adc and power supply v cc supply voltage v cc 3.0 5.5 v v fan supply voltage v vfan 4.5 13.5 v operating supply current i cc fan off 250 500 a shutdown supply current i shdn shutdown 3 10 a 0.125 c temperature resolution 11 bits t rj = +60 c to +100 c-1 +1 t rj = +25 c to +125 c-3 +3 temperature error (note 2) t e t a = +85 c, v cc = +3.3v t rj = -40 c to +125 c-5 +5 c internal reference frequency accuracy +25 -25 % temperature conversion time 0.25 s conversion rate timing error -25 +25 % undervoltage lockout threshold v uvlo v cc falling 2.50 2.80 3.00 v undervoltage lockout threshold hysteresis v hyst 90 mv power-on-reset (por) threshold (v cc ) v cc rising 1.4 2.0 2.5 v por threshold hysteresis 90 mv high level 80 100 120 remote-junction source current i rj low level 8 10 12 a dxn source voltage v dxn 0.7 v
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface _______________________________________________________________________________________ 3 note 1: junction temperature = t a . this implies zero dissipation in pass transistor (no load, or fan turned off). note 2: t rj , remote temperature accuracy is guaranteed by design, not production tested. note 3: guaranteed by design. not production tested. note 4: the MAX6660 includes an smbus timeout, which resets the interface whenever smbclk or smbdata has been low for greater than 25ms. this feature can be disabled by setting bit 2 of the fan gain register at 16h/1bh to a 1. when the timeout is disabled, the minimum clock frequency is dc. note 5: note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of smbclk s falling edge. electrical characteristics (continued) (v cc = +3v to +5.5v, v vfan = +12v, t a = -40 c to +125 c, unless otherwise specified. typical values are at v cc = +3.3v and t a = +25 c.) (note 1) parameter sym b o l conditions min typ max units tach input transition level v vfan = 12v 10.5 v tach input hysteresis v fan = 12v 190 mv current-sense tach threshold 20 ma current-sense tach hysteresis 0.3 ma fan output current 250 ma fan output current limit (note 3) 320 410 ma fan output on-resistance r onf 250ma load 4 ? smbus interface: smbdata, alert , stby , overt logic input low voltage v il v cc = +3.0v to +5.5v 0.8 v v cc = +3.0v 2.2 logic input high voltage v ih v cc = +5.5v 2.6 v input leakage current i_leak v in = gnd or v cc -2 +2 a output low sink current i ol v ol = 0.4v 6 ma input capacitance c in 5pf output high leakage current v oh = 5.5v 1 a serial clock frequency f scl (note 4) 0 100 khz bus free time between stop and start conditions t buf 4.7 s start condition setup time 4.7 s repeat start condition setup time t su:sta 90% to 90% 50 s start condition hold time t hd:sta 10% of smbdata to 90% of smbclk 4 s stop condition setup time t su:sto 90% of smbclk to 10% of smbdata 4 s clock low time t low 10% to 10% 4.7 s clock high time t high 90% to 90% 4 s data setup time t su:dat 90% of smbdata to 10% of smbclk 250 ns data hold time t hd:dat (note 5) 0 s receive smbclk/smbdata rise time t r 1s receive smbclk/smbdata fall time t f 300 ns smbus timeout t timeout smbdata and smbclk time low for reset of serial interface 25 40 ms
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 4 _______________________________________________________________________________________ 1 10 100 temperature error vs. pc board resistance MAX6660 toc01 leakage resistance (m ?) temperature error ( c) 20 -30 -25 -20 -15 -10 -5 0 15 10 5 path = dxp to gnd path = dxp to v cc (+5v) -5 -2 -3 -4 -1 0 1 2 3 4 5 -50 0 50 100 150 MAX6660 toc02 temperature ( c) temperature error ( c) temperature error vs. remote-diode temperature 1 100 10k 1m 10 1k 100k 10m 100m temperature error vs. power-supply noise frequency MAX6660 toc03 frequency (hz) temperature error ( c) 20 -30 -25 -20 -15 -10 -5 0 15 10 5 v in = 100mvp-p v in = square wave applied to v cc with no 0.1 f v cc capacitor v in = 250mvp-p 4.0 -1.5 -1.0 MAX6660 toc04 frequency (hz) temperature error ( c) -0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 1 10 100m 1m 10m 100 1k 10k 100k temperature error vs. common-mode noise frequency v in = 50mvp-p v in = square wave ac-coupled to dxn v in = 100mvp-p v in = 25mvp-p -8 -6 -7 -4 -5 -3 -2 0 -1 1 0102030405060708090100 MAX6660 toc05 dxp-dxn capacitance (nf) temperature error ( c) temperature error vs. dxp-dxn capacitance 0 1 3 2 4 5 MAX6660 toc06 supply voltage (v) standby supply current ( a) 3.0 4.0 4.5 3.5 5.0 5.5 standby supply current vs. supply voltage 3.0 3.9 4.2 3.3 3.6 4.5 4.8 5.1 5.4 MAX6660 toc07 supply voltage (v) average supply current ( a) 100 200 300 400 average supply current vs. supply voltage typical operating characteristics (v cc = +3.3v, t a = +25 c, unless otherwise noted.)
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface _______________________________________________________________________________________ 5 pin name function 1 vfan fan drive power-supply input. 4.5v to 13.5v. 2v cc supply voltage input. +3v to +5.5v. bypass v cc to ground with a 0.1f capacitor. 3 dxp input: remote-junction anode. place a 2200pf capacitor between dxp and dxn for noise filtering. 4 dxn input: remote-junction cathode. dxn is internally biased to a diode voltage above ground. 5 fan open-drain output to fan low side. connect a minimum 1f capacitor between fan and vfan. 6 add1 smbus address select pin. add0 and add1 are sampled upon power-up. 7 pgnd power ground 8 agnd analog ground 9 overt overtemperature shutdown output. active-low output (programmable for active high if desired). open drain. 10 add0 smbus slave address select pin. add0 and add1 are sampled upon power-up. 11 alert smbus alert (interrupt) output. open-drain, active-low output. 12 smbdata smbus serial data input/output. open drain. 13 gain gain control. connect an external resistor from gain to v cc to reduce the gain of the current-sense mode. 14 smbclk smbus clock line from controller. this line tolerates inputs up to v cc even if MAX6660 is not powered. 15 stby hardware standby input. drive stby low to reduce supply current. temperature and comparison data are retained in standby mode. 16 tach in fan tachometer input. tolerates voltages up to vfan. detailed description the MAX6660 is a remote temperature sensor and fan controller with an smbus interface. the MAX6660 con- verts the temperature of a remote-junction temperature sensor to a 10-bit + sign digital word. the remote tem- perature sensor can be a diode-connected transistor, such as a 2n3906, or the type normally found on the substrate of many processors ics. the temperature information is provided to the fan-speed regulator and is read over the smbus interface. the temperature data, through the smbus, can be read as a 10-bit + sign two s complement word with a 0.125 c resolution (lsb) and is updated every 0.25s. the MAX6660 incorporates a closed-loop fan controller that re gulates fan speed with tachometer feedback. the temperature information is compared to a threshold and range setting, which enables the MAX6660 to automati- cally set fan speed proportional to temperature. full con- trol of these modes is available, including being able to open either the thermal control loop or the fan control loop. figure 1 shows a simplified block diagram. adc the adc is an averaging type that integrates over a 60ms period with excellent noise rejection. a bias cur- rent is steered through the remote diode, where the for- ward voltage is measured, and the temperature is com- puted. the dxn pin is the cathode of the remote diode and is biased at 0.65v above ground by an internal diode to set up the adc inputs for a differential mea- surement. the worst-case dxp-dxn differential input voltage range is 0.25v to 0.95v. excess resis tance in series with the remote diode causes about +1/2 c error per ohm. likewise, 200mv of offset voltage forced on dxp-dxn causes approximately 1 c error. a/d conversion sequence a conversion sequence is initiated every 250ms in the free-running autoconvert mode (bit 6 = 0 in the configuration register) or immediately by writing a one- shot command. the result of the new measurement is available after the end of conversion. the results of the previous conversion sequence are still available when the adc is converting. remote-diode selection temperature accuracy depends on having a good- quality, diode-connected small-signal transistor. accuracy has been experimentally verified for all devices listed in table 1. the MAX6660 can also direct- pin description
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 6 ________________________________________________________________________________________ n fan fan tach in vfan fan-speed regulator mux dxp dxn t high t low configuration fan count divisor (fc) fan speed limit (fs) fan gain (fg) t fan (ft) fan conversion rate (fcr) mode (m) fan limit (fl) fan-speed control (fsc) status t hyst comparat0r t max thermal open/ closed loop fan open/ closed loop fan control circuit remote data temperature registers smbclk smbdata add0 add1 adc central logic smbus interface address decoder overt alert figure 1. MAX6660 block diagram
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface _______________________________________________________________________________________ 7 ly measure the die temperature of cpus and other ics that have on-board temperature-sensing diodes. the transistor must be a small-signal type with a rela- tively high forward voltage. otherwise, the a/d input range could be violated. the forward voltage must be greater than 0.25v at 10a. check to ensure this is true at the highest expected temperature. the forward volt- age must be less than 0.95v at 100a. check to ensure that this is true at the lowest expected temperature. large power transistors, power diodes, or small-signal diodes must not be used. also, ensure that the base resistance is less than 100 ? . tight specifications for forward current gain (50 < <150, for example) indi- cate that the manufacturer has good process controls and that the devices have consistent vbe characteris- tics. bits 5 2 of the mode register can be used to adjust the adc gain to achieve accurate temperature measurements with diodes not included in the recom- mended list or to individually calibrate the MAX6660 for use in specific control systems. thermal mass and self-heating when measuring the temperature of a cpu or other ic with an on-chip sense junction, thermal mass has virtu- ally no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle. when measuring temperature with discrete remote sen- sors, smaller packages (e.g., a sot23) yield the best thermal response times. take care to account for ther- mal gradients between the heat source and the sensor, and ensure that stray air currents across the sensor package do not interfere with measurement accuracy. self-heating does not significantly affect measurement accuracy. remote-sensor self-heating due to the diode current source is negligible. adc noise filtering the adc is an integrating type with inherently good noise rejection, especially of low-frequency signals such as 60hz/120hz power-supply hum. micropower operation places constraints on high-frequency noise rejection; therefore, careful pc board layout and proper external noise filtering are required for high-accuracy remote mea- surements in electrically noisy environments. high-frequency emi is best filtered at dxp and dxn with an external 2200pf capacitor. this value can be increased to about 3300pf (max), including cable capacitance. capacitance higher than 3300pf intro- duces errors due to rise time of the switched current source. nearly all noise sources tested cause the adc measurements to be higher than the actual tempera- ture, typically by +1 c to +10 c, depending on the fre- quency and amplitude. pc board layout follow these guidelines to reduce the measurement error of the temperature sensors: 1) place the MAX6660 as close as is practical to the remote diode. in noisy environments, such as a computer motherboard, this distance can be 4in to 8in (typ). this length can be increased if the worst noise sources are avoided. noise sources include crts, clock generators, memory buses, and isa/pci buses. 2) do not route the dxp-dxn lines next to the deflec- tion coils of a crt. also, do not route the traces across fast digital signals, which can easily intro- duce +30 c error, even with good filtering. 3) route the dxp and dxn traces in parallel and in close proximity to each other, away from any high- er voltage traces, such as +12vdc. leakage cur- rents from pc board contamination must be dealt with carefully since a 20m ? leakage path from dxp to ground causes about +1 c error. if high- voltage traces are unavoidable, connect guard traces to gnd on either side of the dxp-dxn traces (figure 2). 4) route through as few vias and crossunders as pos- sible to minimize copper/solder thermocouple effects. 5) when introducing a thermocouple, make sure that both the dxp and the dxn paths have matching thermocouples. a copper-solder thermocouple exhibits 3v/ c, and it takes about 200v of voltage error at dxp-dxn to cause a +1 c measurement error. adding a few thermocouples causes a negligi- ble error. 6) use wide traces. narrow traces are more inductive and tend to pick up radiated noise. the 10mil widths and spacings that are recommended in figure 2 are not absolutely necessary, as they offer only a minor manufacturer model no. central semiconductor (usa) 2n3904, 2n3906 fairchild semiconductor (usa) 2n3904, 2n3906 rohm semiconductor (japan) sst3904 samsung (korea) kst3904-tf siemens (germany) smbt3904 zetex (england) fmmt3904ct-nd table 1. remote-sensor transistor note: transistors must be diode connected (base shorted to collector).
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 8 _______________________________________________________________________________________ improvement in leakage and noise over narrow traces. use wider traces when practical. 7) add a 50 ? resistor in series with v cc for best noise filtering (see typical operating circuit ). pc board layout checklist place the MAX6660 close to the remote-sense junc- tion. keep traces away from high voltages (+12v bus). keep traces away from fast data buses and crts. use recommended trace widths and spacings. place a ground plane under the traces. use guard traces flanking dxp and dxn and connect- ing to gnd. place the noise filter and the 0.1f v cc bypass capacitors close to the MAX6660. twisted-pair and shielded cables use a twisted-pair cable to connect the remote sensor for remote-sensor distances longer than 8in or in very noisy environments. twisted-pair cable lengths can be between 6ft and 12ft before noise introduces excessive errors. 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. at the device, connect the twisted pair to dxp and dxn and the shield to gnd. leave the shield unconnected at the remote sensor. for very long cable runs, the cable s parasitic capaci- tance often provides noise filtering, so the 2200pf capacitor can often be removed or reduced in value. cable resistance also affects remote-sensor accuracy. for every 1 ? of series resistance, the error is approxi- mately +1/2 c. low-power standby mode standby mode reduces the supply current to less than 10a by disabling the adc, the control loop, and the fan driver. enter hardware standby mode by forcing stby low, or enter software standby by setting the run/stop bit to 1 in the configuration byte register. hardware and software standbys are very similar; all data is retained in memory, and the smb interface is alive and listening for smbus commands. the only dif- ference is that in software standby mode, the one-shot command initiates a conversion. with hardware stand- by, the one-shot command is ignored. activity on the smbus causes the device to draw extra supply current. driving stby low overrides any software conversion command. if a hardware or software standby command is received while a conversion is in progress, the con- version cycle is interrupted, and the temperature regis- ters are not updated. the previous data is not changed and remains available. smbus digital interface from a software perspective, the MAX6660 appears as a set of byte-wide registers that contain temperature data, alarm threshold values, and control bits. the device responds to the same smbus slave address for access to all functions. the MAX6660 employs four standard smbus protocols: write byte, read byte, send byte, and receive byte (figures 3, 4, 5) to program the alarm thresholds, read the temperature data, and read and write to all fan con- trol loop registers. the shorter receive byte protocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruction. use caution with the shorter protocols in multimaster systems, since a second master could overwrite the command byte without informing the first master. figure 2. recommended dxp-dxn pc trace minimum 10mils 10mils 10mils 10mils gnd dxn dxp gnd temp. ( c) digital output +127 0111 1111 111 +125.00 0111 1101 000 +25 0001 1001 000 +0.125 0000 0000 001 0 0000 0000 000 -0.125 1111 1111 111 -25 1110 0111 111 -40 1101 1000111 table 2. temperature data format (two s complement)
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface _______________________________________________________________________________________ 9 figure 4. smbus write timing diagram figure 5. smbus read timing diagram ack 7 bits address ack wr 8 bits data ack 1 p 8 bits s command write byte format read byte format send byte format receive byte format slave address: equiva- lent to chip-select line of a 3-wire interface command byte: selects which register you are writing to data byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) ack 7 bits address ack wr s ack 8 bits data 7 bits address rd 8 bits /// p s command slave address: equiva- lent to chip-select line command byte: selects which register you are reading from slave address: repeated due to change in data- flow direction data byte: reads from the register set by the command byte ack 7 bits address wr 8 bits command ack p s ack 7 bits address rd 8 bits data /// p s command byte: sends com- mand with no data, usually used for one-shot command data byte: reads data from the register commanded by the last read byte or write byte transmission; also used for smbus alert response return address s = start condition shaded = slave transmission p = stop condition /// = not acknowledged smbclk a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave ab cd e fg h i j smbdata t su:sta t hd:sta t low t high t su:dat klm t su:sto t buf e = slave pulls smbdata line low f = acknowledge bit clocked into master g = msb of data clocked into master h = lsb of data clocked into master i = master pulls data line low j = acknowledge clocked into slave k = acknowledge clear pulse j = stop condition, data executed by slave k = new start condition smbclk ab cd e fg h i j k smbdata t su:sta t hd:sta t low t high t su:dat t hd:dat t su:sto t buf a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave e = slave pulls smbdata line low l m f = acknowledge bit clocked into master g = msb of data clocked into slave h = lsb of data clocked into slave i = slave pulls smbdata line low j = acknowledge clocked into master k = acknowledge clock pulse l = stop condition, data executed by slave m = new start condition figure 3. smbus protocols
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 10 ______________________________________________________________________________________ the smbus interface includes a timeout, which resets the interface any time the data or clock line is held low for more than 35ms, ensuring that the MAX6660 can never lock the bus. remote temperature data register two registers, at addresses 00h and 01h, store the measured temperature data from the remote diode. the data format for the remote-diode temperature is 10 bit + sign, with each bit corresponding to 0.125 c, in two s complement format (table 2). register 01h contains the sign bit and the first 7 bits. bits 7, 6, 5 of register 00h are the 3lsbs. if the two registers are not read at the same time, their contents may be the result of two dif- ferent temperature measurements leading to erroneous temperature data. for this reason, a parity bit has been added to the 00h register. bit 4 of this is zero if the data in 00h and 01h are from the same temperature conver- sion and are 1 if they are not. the remaining bits are don t cares. when reading temperature data, register 01h must be read first. alarm threshold registers the MAX6660 provides four alarm threshold registers that can be programmed with a two s complement tem- perature value with each bit corresponding to 1 c. the registers are t high , t low , t max , and t hyst . if the measured temperature equals or exceeds t high , or is less than t low , an alert interrupt is asserted. if the measured temperature equals or exceeds t max , the overt output is asserted (see over-temperature output ( overt) section). if alert and overt are acti- vated by the temperature exceeding t max , they can only be deasserted by the temperature dropping below t hyst . the por state for t high is +127 c, for t low is - 55 c, for t max is +100 c, and for t hyst is +95 c. over-temperature output ( overt ) the MAX6660 has an over-temperature output ( overt ) that is set when the remote-diode temperature crosses the limits set in the t max register. it is always active if the remote-diode temperature exceeds t max . the overt line clears when the temperature drops below t hyst . bit 1 of the configuration register can be used to mask the overt output. typically, the overt output is connected to a power-supply shutdown line to turn system power off. at power-up, overt defaults to active-low but the polarity can be reversed by setting bit 5 of the configuration register. the overt line can be taken active, either by the MAX6660 or driven by an external source. an external source can be masked by bit 2 of the configuration register. when overt is active, the fan loop forces the fan to full speed and bit 1 of the status register is set. diode fault alarm a continuity fault detector at dxp detects an open cir- cuit between dxp and dxn. if an open or short circuit exists, register 01h is loaded with 000 0000. additionally, if the fault is an open circuit, bit 2 of the status byte is set to 1 and the alert condition is acti- vated at the end of the conversion. immediately after por, the status register indicates that no fault is pre- sent until the end of the first conversion. alert interrupts the alert interrupt output signal is activated (unless it is masked by bit 7 in the configuration register) when- ever the remote-diode s temperature is below t low or exceeds t high . a disconnected remote diode (for con- tinuity detection), a shorted diode, or an active overt also activates the alert signal. the activation of the alert signal sets the corresponding bits in the status register. there are two ways to clear the alert : send- ing the alert response address or reading the status register. the interrupt does not halt automatic conversions. new temperature data continues to be available over the smbus interface after alert is asserted. alert is an active-low open-drain output so that devices can share a common interrupt line. the interrupt is updated at the end of each temperature conversion so, after being cleared, reappears after the next temperature conver- sion, if the cause of the fault has not been removed. by setting bit 0 in the configuration register to 1, the status register can only be cleared by sending the smbus alert response address (see alert response address section). prior to taking corrective action, always check to ensure that an interrupt is valid by reading the current temperature. to prevent recurring interrupts, the MAX6660 asserts alert only once per crossing of a given temperature threshold. to enable a new interrupt, the value in the limit register that trig- gered the interrupt must be rewritten. other interrupt conditions can be caused by crossing the opposite temperature threshold, or a diode fault can still cause an interrupt. example: the remote temperature reading crosses t high , activating alert . the host responds to the interrupt and reads the alert response address, clear- ing the interrupt. the system may also read the status byte at this time. if the condition persists, the interrupt reappears. finally, the host writes a new value to t high . this enables the device to generate a new t high interrupt if the alert condition still exists.
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface ______________________________________________________________________________________ 11 alert response address the smbus alert response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. upon receiving an alert interrupt signal, the host master can broadcast a receive byte transmission to the alert response slave address (see slave addresses section). then, any slave device that gener- ated an interrupt attempts to identify itself by putting its own address on the bus (table 3). the alert response can activate several different slave devices simultaneously, similar to the i 2 c general call. if more than one slave attempts to respond, bus arbitration rules apply, and the device with the lower address code wins. the losing device does not gener- ate an acknowledge and continues to hold the alert line low until cleared. (the conditions for clearing an alert vary depending on the type of slave device.) successful completion of the alert response protocol clears the interrupt latch, provided the condition that caused the alert no longer exists. if the condition still exists, the device reasserts the alert interrupt at the end of the next conversion. table 3. read format for alert response address command byte functions the 8-bit command byte register (table 4) is the mas- ter index that points to the other registers within the MAX6660. the register s por is 0000 0000, so that a receive byte transmission (a protocol that lacks the command byte) that occurs immediately after por returns the current remote temperature data. one-shot the one-shot command immediately forces a new conver- sion cycle to begin. in software standby mode (run/stop bit = high), a new conversion is begun, after which the device returns to standby mode. if a conversion is in progress when a one-shot command is received, the command is ignored. if a one-shot command is between conversions, in autoconvert mode (run/stop bit = low), a new conversion begins immediately. configuration byte functions the configuration byte register (table 5) is used to mask (disable) the alert signal to place the device in software standby mode, to change the polarity of overt , to set MAX6660 to thermal open/closed-loop mode, to inhibit the overt signal, to mask overt out- put, and to clear the alert signal. the MAX6660 has a write protection feature (bit 4) that prohibits write com- mands to bits 6 3 of the configuration register. it also prohibits writes to the t max , t hyst , and fan conversion rate registers. status byte functions the status byte (table 6) reports several fault condi- tions. it indicates when the fan driver transistor of the MAX6660 has overheated and/or is thermal shutdown, when the temperature thresholds, t low and t high , have been exceeded, and whether there is an open cir- cuit in the dxp-dxn path. the register also reports the state of the alert and overt lines and indicates when the fan driver is fully on. the final bit in the status register indicates when a fan failure has occurred. after por, the normal state of the flag bits is zero, assuming no alert or overtemperature conditions are present. bits 2 through 6 of the status register are cleared by any successful read of the status register, unless the fault persists. the alert output follows the status flag bit. both are cleared when successfully read, but if the condition still exists, the alert is reasserted at the end of the next conversion. the MAX6660 incorporates collision avoidance so that completely asynchronous operation is allowed between smbus operations and temperature conversions. when autoconverting, if the t high and t low limits are close together, it is possible for both high-temperature and low-temperature status bits to be set, depending on the amount of time between status read operations. in these circumstances, it is best not to rely on the sta- tus bits to indicate reversals in long-term temperature changes. instead, use a current temperature reading to establish the trend direction. manufacturer and device id codes two rom registers provide manufacturer and device id codes. reading the manufacturer id returns 4d, which is the ascii code m (for maxim). reading the device id returns 09h, indicating the MAX6660 device. if read word 16-bit smbus protocol is employed bit name function 7 (msb) add7 6 add6 5 add5 4 add4 3 add3 2 add2 1 add1 provide the current MAX6660 slave address 0 (lsb) 1 logic 1 i 2 c is a trademark of philips corp.
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 12 ______________________________________________________________________________________ (rather than the 8-bit read byte), the lsb contains the data and the msb contains 00h in both cases. slave addresses the MAX6660 can be programmed to have one of nine different addresses by pin strapping add0 and add1 so that up to nine MAX6660s can reside on the same bus without address conflicts. see table 7 for address information. the address pin state is checked at por only, and the address data stays latched to reduce quiescent supply current due to the bias current needed for high-z state detection. the MAX6660 also responds to the smbus alert response slave address (see the alert response address section). por and uvlo the MAX6660 has a volatile memory. to prevent unreli- able power-supply conditions from corrupting the data in memory and causing erratic behavior, a por voltage detector monitors v cc and clears the memory if v cc falls below 1.91v (typ, see electrical characteristics ). when power is first applied and v cc rises above 2.0v (typ), the logic blocks begin operating, although reads and writes at v cc levels below 3.0v are not recom- mended. a second v cc comparator, the adc under- voltage lockout (uvlo) comparator prevents the adc from converting until there is sufficient headroom (v cc = 2.8v typ). the spor software por command can force a power-on reset of the MAX6660 registers through the serial interface. use the send byte protocol with command = fch. registers command por state function rrl 00h 00000000 read remote temperature low byte (3msbs) rrh 01h 00000000 read remote temperature high byte (sign bit and first 7 bits) rsl 02h 00000000 read status byte rcl/wcl 03h/09h 00000000 read/write configuration byte rfcr/wfcr 04h/0ah 00000010 read/write fan-conversion rate byte rtmax/wtmax 10h/12h 01100100 at +100 c read/write remote t max rthyst/wthyst 11h/13h 01011111 at +95 c read/write remote t hyst rthigh/wthigh 07h/0dh 01111111 at +127 c read/write remote t high rtlow/wtlow 08h/0eh 11001001 at -55 c read/write remote t low spor fch n/a write software por osht 0fh n/a write one-shot temperature conversion rtfan/wtfan 14h/19h 00111100 at +60 c read/write fan-control threshold temperature t fan rfsc/wfsc 15h/1ah 00000000 read/write fan-speed control rfg/wfg 16h/1bh 10000000 read/write fan gain rftc 17h 00000000 read fan tachometer count rftcl/wftcl 18h/1ch 11111111 read/write fan tachometer count limit (fan failure limit) rfcd/wfcd 1dh/1eh 00000001 read/write fan count divisor rfs/wfs 1fh/20h 11111111 read/write full-scale register rm/wm fah/fbh 00000000 read/write mode register id code feh 01001101 read manufacturer id code id code 9dh 00001001 read device id code table 4. command-byte bit assignments
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface ______________________________________________________________________________________ 13 bit name por state description 7(msb) alert mask 0 when set to 1, alert is masked from internally generated errors. 6 run/stop 0 when set to 1, the MAX6660 enters low-power standby. 5 overt polarity 0 0 provides active low, 1 provides active high. 4 write protect 0 when set to 1, write protect is in effect for the following applicable registers: 1. configuration register bits 6, 5, 4, 3 2. t max register 3. t hyst register 4. fan conversion rate register 3 thermal closed/ open loop 0 when set to 1, the thermal loop is open. the fan speed control retains the last closed-loop value unless overwritten by a bus command (in closed loop, the fan speed control is read only). if fan mode is set to open loop by writing a 1 to bit 0 of the fan gain register, then this bit is automatically set. 2 overt input inhibit 0 when set to 1, an external signal on overt is masked from bit 1 of the status register. 1 mask overt output 0 mask the overt output from an internally generated overtemperature error. 0 alert clear mode 0 when 0, reading the status register clears or sending an alert response request clears alert (if the fault condition is no longer true). when set high, only an alert response request clears alert . bit name por state description 7 (msb) MAX6660 overheat 0 when high, indicates that the fan driver transistor of the MAX6660 has overheated (temp > +150 c) and is in thermal shutdown. the fan driver remains disabled until temperature falls below +140 c. 6 alert 0 when high, indicates alert has been activated (pulled low), regardless of cause (internal or external). 5 fan driver full scale 0 when high, indicates the fan driver is at full scale. only valid in fan closed-loop mode (register fg b170 = 0). set to high in fan open-loop mode (register fg b170 = 1). 4 remote high 0 when high, the remote-junction temperature exceeds the temperature in the remote high register. 3 remote low 0 when high, the remote-junction temperature is lower than the temperature in the remote low register. 2 diode open 0 when high, the remote-junction diode is open. 1 overt 0 when high, indicates that overt has been activated, regardless of cause (internal or external). 0 fan failure 0 when high, indicates the count in the fan tachometer count register is higher than the limit set in the fan tachometer count limit register. table 5. configuration-byte bit assignments table 6. status-byte bit assignments
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 14 ______________________________________________________________________________________ power-up defaults include: interrupt latch is cleared. adc begins autoconverting. command register is set to 00h to facilitate quick internal receive byte queries. t high and t low registers are set to +127 c and -55 c, respectively. t hyst and t max are set to +95 c and +100 c, respectively. fan control the fan-control function can be divided into the thermal loop, the fan-speed-regulation loop (fan loop), and the fan-failure sensor. the thermal loop sets the desired fan speed based on temperature while the fan-speed-regu- lation loop uses an internally divided down reference oscillator to synchronize to and regulate the fan speed. the fan-speed-regulation loop includes the fan driver and the tachometer sensor. the fan-failure sensor pro- vides a fan fail alarm that signals when the fan tachometer count is greater than the fan tachometer value, which corresponds to a fan going slower than the limit. the fan driver is an n-channel, 4 ? , 320ma mosfet with a 16v maximum v ds whose drain termi- nal connects to the low side of the fan. the tachometer sensor (tach in) of the MAX6660 is driven from the tachometer output of the fan and provides the feed- back signal to the fan-speed-regulation loop for control- ling the fan speed. for fans without tachometer outputs, the MAX6660 can generate its own tachometer pulses by monitoring the commutating current pulses (see commutating current pulses section). thermal loop thermal closed loop the MAX6660 can be operated in a complete closed- loop mode, with both the thermal and fan loops closed, where the remote-diode sensor temperature directly controls fan speed. setting bit 3 of the configuration register to zero places the MAX6660 in thermal closed loop (figure 6). the remote-diode temperature sensor is updated every 250ms. the value is stored in a tem- porary register (tempdata) and compared to the pro- grammed temperature values in the t high , t low , t hyst , t max , and t fan registers to produce the error outputs overt and alert . the fan conversion rate (fcr) register (table 8) can be programmed to update the tempdata every 0.25s add0 add1 address gnd gnd 0011 000 gnd high-z 0011 001 gnd v cc 0011 010 high-z gnd 0101 001 high-z high-z 0101 010 high-z v cc 0101 011 v cc gnd 1001 100 v cc high-z 1001 101 v cc v cc 1001 110 table 7. por slave address decoding (add0 and add1) update fcr 0.25s to 16s tempdata fsc t fan fg 4/5/6 bits fan control driver circuit figure 6. MAX6660 thermal loop
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface ______________________________________________________________________________________ 15 to 16s and stores the data in an update register (update). this enables control over timing of the ther- mal feedback loop to optimize stability. the fan threshold (t fan ) register value is subtracted from the update register value. if update exceeds t fan temperature, then the fan-speed control (fsc) register (table 9) stores the excess temperature in the form of a 7-bit word with an lsb of 0.5 c for bits 4 0, with bit 5 = 16 c. if the difference between the t fan and update registers is higher than 32 c, then bit 6 is set to 1, along with bits 5 1. in thermal closed loop, the fan speed control register is read only. the fan gain (fg) register (table 10) determines the number of bits used in the fan-speed control register. this gain can be set to 4, 5, or 6. if bits 6 and 5 are set to 10, all 6 bits of tempdata are used directly to pro- gram the speed of the fan so that the thermal loop has a control range of +32 c with 64 temperature steps from fan off to full fan speed. if bits 6 and 5 are set to 01, the thermal control loop has a control range of 16 c with 32 temperature steps from fan off to full fan speed. if bits 6 and 5 are set to 00, the thermal control loop has a control range of 8 c with 16 temperature steps from fan off to full fan speed. thermal open loop setting bit 3 of the configuration register (table 5) to 1 places the MAX6660 in thermal open loop. in thermal open-loop mode, the fsc register is read/write and con- tains the 7-bit result of update subtracted from t fan . in fan open loop, the fsc register programs fan voltage with acceptable values from 0 to 64 (40h). for example, in fan open-loop mode, 0 corresponds to zero output and 40h corresponds to full fan voltage, for example (11.3v, typ). proportional control is available over the 0 to 63 (3fh) range with 64 (40h) forcing unconditional full speed. in fan closed-loop mode, 0 corresponds to zero fan speed and 10h corresponds to 100% fan speed, when the fg register is set to 4 bits, 20h at 5 bits, and 3fh at 6 bits. fan loop the fan controller (figure 7) is based on an up/down counter where there is a reference clock representing the desired fan speed counting up, while tachometer pulses count down. the reference clock frequency is divided down from the MAX6660 internal clock to a fre- quency of 8415hz. this clock frequency is further divided by the fan full-scale (fs) register (table 11), which is limited to values between 127 to 255, for a data binary fan update rate (hz) seconds between updates 00h 00000000 0.0625 16 01h 00000001 0.125 8 02h 00000010 0.25 4 (por) 03h 00000011 0.5 2 04h 00000100 1 1 05h 00000101 2 0.5 06h 00000110 4 0.25 table 8. fan conversion update rate register/ address fsc (15h = read, 1ah = write) command read/write fan dac register bit 7 n/a 6 overflow bit 5 (msb) 4 data 3 data 2 data 1 data 0 data por state 0 0 000000 table 9. fan-speed control register (rfsc/w fsc) note: in thermal closed-loop mode, the fan dac is read only and contains the difference between the measured temperature and the fan threshold temperature. the lsb is 0.5 c and bit 5 is 16 c. if the difference is higher than 32 c, then bit 6 is set to 1, together with bits 5 0. bit 6 can be regarded as an overflow bit for differences higher than 32 c. bit 7 is always zero. the fsc register can be programmed directly in thermal open mode. in fan closed-loop mode, fsc programs fan speed with accept- able values from 0 to 10h, when fg is set to 4 bits or 20h when fg is set to 5 bits, or 3f when fg is set to 6 bits. in fan ope n- loop mode, fsc programs fan voltage with acceptable values from 0 to 64 (40h). for example, in fan closed-loop mode, zero corresponds to zero fan speed and 10h corresponds to 100% fan speed. in fan open-loop mode, zero corresponds to zero volts out and 40h corresponds to full fan voltage (11.3v typ).
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 16 ______________________________________________________________________________________ range of reference clock full-scale frequencies from 33hz to 66hz. a further division is performed to set the actual desired fan speed. this value appears in the fan- speed control register in thermal closed-loop mode. if the thermal loop is open, but the fan-speed control loop is closed, this value is programmable in the fan dac. when in fan open-loop mode (which forces the thermal loop to open), the fsc register becomes a true dac, programming the voltage across the fan from zero to nearly 12v to v vfan . the tachometer input (tach in) includes a program- mable (1/2/4/8) prescalar. the divider ratio for the (1/2/4/8) prescalar is stored in the fan count divisor (fcd) register (table 12). in general, the values in fc should be set such that the full-speed fan frequency divided by the prescalar fall in the 33hz to 66hz range. the (up/dn) counter has six stages that form the input of a 6-bit resistive ladder dac whose voltage is divided down from v vfan . this dac determines the voltage applied to the fan. internal coding is structured such that when in fan closed-loop mode (which includes thermal closed loop) that higher values in the 0 to 32 range correspond to higher fan speeds and greater voltage across the fan. in fan open-loop mode (which forces thermal open loop) acceptable values range from 0 to 63 (3fh) for proportional control; a value of 64 (40h) commands unconditional full speed. register/ address fg (16h = read, 1bh = write) command read/write fan gain register bit 7 reserved 6 fan gain 5 fan gain 43 2 smbus timeout 1 fan feedback mode 0 fan driver mode por state 1 0 0 x x x 0 0 table 10. fan gain register (rfg/wfg) notes: bit 7: reserved. always 1. if bit 7 is written to zero, then bits 7, 6, and 5 are set to 100. bits 6, 5: fan gain of the fan loop, where 00 = 8 c with resolution = 4 bits. this means that the fan reaches its full-scale (maximum) speed when there is an 8 c difference between the remote-diode temperature and the value stored in tfan , 01 = 16 c, with a 5-bit resolution and 10 = 32 c with a 6-bit resolution. bits 4, 3: reserved. bit 2: smbus timeout. when 1, the smbus timeout is disabled. this permits full i 2 c compatibility with minimum clock frequency to dc. bit 1: fan feedback mode. when bit 1 is set to 1, the fan loop uses driver current sense rather than tachometer feedback. bit 0: fan driver mode. when bit 0 is set to 1, the fan driver is in fan open-loop mode. in this mode, the fan dac programs the fan voltage rather than the fan speed. tachometer feedback is ignored, and the user must consider minimum fan drive and startup issues. thermal open loop is automatically set to 1 (see configuration register). fan fail (bit 0 of the status registe r) is set to 1 in this mode and should be ignored. register/ address fs (1fh = read, 20h = write) command read/write maximum temperature limit byte bit 7 (msb) 6 data bit 5 data bit 4 data bit 3 data bit 2 data bit 1 data bit 0 data bit por state 1 1 1 1 1 1 1 1 table 11. fan full-scale register (rfs/wfs) note: this register determines the maximum reference frequency at the input of the phase detector. it controls a programmable divider that can be set anywhere between 127 and 255. the value in this register must be set in accordance with the proce- dure described in the tach in section (equivalent to 8415/(fan frequency/fan count divisor)). programmed value below 127 defaults to 127. por value is 255.
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface ______________________________________________________________________________________ 17 register/ address fcd (1dh = read, 1eh = write) command read limit/failure register bit 7 6543210 por state 00000001 table 12. fan count divisor register (rfcd/wfcd) notes: this byte sets the prescalar division ratio for tachometer or current-sense feedback. (this register does not apply to the tach signal used in the fan-speed register). select this value such that the fan frequency (rpm/60 x number of poles) divided by the fcd falls in the 33hz to 66hz range. see tach in section. bits 1, 0: 00 = divide by 1, 01 = divide by 2, 10 = divide by 4, 11 = divide by 8. n tempdata fg 4/5/6 ref frequency 8415hz fs 127/255 1/64 counter ftc ftcl comparator fcd 1/2/4/8 fan open/closed loop up/down driver dac fan fail vfan fan tach in figure 7. MAX6660 fan loop functional diagram
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 18 ______________________________________________________________________________________ register/ address fl (18h = read, 1ch = write) command read limit/failure register bit 7 (msb) 6 5 4 3 2 1 0 por state 1 1 1 1 1 1 1 1 table13. fan tachometer count limit (rftcl/wftcl) fan conversion rate byte the fcr register (table 8) programs the fan s update time interval in free-running autonomous mode ( run / stop = 0). the conversion rate byte s por state is 02h (0.25hz). the MAX6660 uses only the 3lsbs of this register. the 4msbs are don t cares. the update rate tolerance is 25% (max) at any rate setting. fan closed loop in the thermal open loop but fan closed-loop mode, the feedback loop can be broken and the temperature data read directly. after performing external manipulations, the result can be injected back into the fan control loop by writing to the fsc register to control fan speed. fan closed-loop mode is selected by setting bit 0 of the fg to zero. fan open loop in fan control open-loop mode, selected by setting bit 0 of the fg register to 1, the gain block is bypassed and the fsc register is used to program the fan voltage rather than the fan speed. in the fan open-loop mode, both the temperature feedback loop and fan-speed control loop are broken, which results in the tach in input becoming disabled. a direct voltage can be applied after reading the temperature, using the fsc register, to the fan that provides more flexibility in exter- nal control algorithms. by selecting fan open-loop mode, the MAX6660 automatically invokes thermal open-loop mode. fan driver the fan driver consists of an amplifier and low-side nmos device whose drain is connected to fan and is the input from the low side of the fan. the fet has a typical 4 ? on-resistance with a typical 320ma maxi- mum current limit. the driver has a thermal shutdown sensor that senses the driver s temperature. it shuts down the driver if the temperature exceeds +150 c. the driver is reactivated once the temperature has dropped below +140 c. tach in the tach in input connects directly to the tachometer output of a fan. most commercially available fans have two tachometer pulses per revolution. the tachometer input is fully compatible with tachometer signals, which are pulled up to v vfan . commutating current pulses when a fan does not come equipped with a tachometer output, the MAX6660 uses commutating generated cur- rent pulses for speed detection. this mode is entered by setting the fg register s bit 1 to 1. an internal cur- rent pulse is generated whenever a step increase occurs in the fan current. connecting an external resis- tor between the gain pin and v cc can reduce the sen- sitivity of current pulses to changes in fan current. in general, the lower the resistor value, then the lower the sensitivity, and the fan is easier to turn on and can use a smaller external capacitor across its terminals. a suit- able resistor range is 1k ? to 5k ? . fan-failure detection the MAX6660 detects fan failure by comparing the value in the fan tachometer count (ftc) register, a read only register, with a limit stored in the fan tachometer count limit (ftcl) register (table 13). a counter counts the number of on-chip oscillator pulses between successive tachometer pulses and loads the ftc register every time a tachometer pulse arrives. if the value in ftc is greater than the value in ftcl, a failure is indicated. in fan closed loop, a flag is activat- ed when the fan is at full speed. set the fan tachometer limit byte to: f l = 8415/[n ? f] where n = fan fail ratio and f = frequency of fan tachometer. the factor n is less than 1 and produces a fan failure indication when the fan should be running at full speed but is only reaching a factor n of its expected frequen- cy. the factor n is typically set to 0.75 for all fan note: the fan limit register is programmed with the maximum speed that is compared against the value in the fs register (address 17) to produce an error output to the status register.
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface ______________________________________________________________________________________ 19 speeds except at very low speeds where a fan failure is indicated by an overflow of the fan speed counter rather than f l . the overflow flag cannot be viewed sep- arately in the status byte but is ored with bit 0, the fan fail bit. applications information mode register resistance in series with the remote-sensing junction causes conversion errors on the order of 0.5 c per ohm. the MAX6660 mode register gives the ability to elimi- nate the effects of external series resistance of up to several hundred ohms on the remote temperature mea- surement and to adjust the temperature measuring adc to suit different types of remote-diode sensor. for systems using external switches or long cables to con- nect to the remote sensor, a parasitic resistance can- cellation mode can be entered by setting mode register bit 7 = 1. this mode requires a longer conversion time and so can only be used for fan conversion rates of 1hz or slower. bits 6, 1, and 0 are reserved. use bits 5 2 to adjust the adc gain to achieve accurate temper- ature measurements with diodes not included in the recommended list or to individually calibrate the MAX6660 for use in specific control systems. these bits adjust gain to set the temperature reading at +25 c, using two s complement format reading. bit 5 is the sign (1 = increase, 0 = decrease), bit 4 = 2 c shift, bit 3 = 1 c shift, bit 2 = 1/2 c shift. general programming techniques the full-scale range of the fan regulation loop is designed to accommodate fans operating between the 1000rpm to 8000rpm range of different fans. an on- chip 8415hz oscillator is used to generate the 33hz to 66hz reference frequency. choose the prescalar such that the fan full-speed frequency divided by the prescalar falls in the 33hz to 66hz range. the full-scale reference frequency is further divided by the value in the fsc register to the desired fan frequency [read: speed]. 1) determine the fan s maximum tachometer frequency: where poles = number of tachometer poles (pulses per revolution). most fans are two poles; therefore, two pulses per revolution. 2) set the programmable fcd to a value p so that the above frequency falls in the 33hz to 66hz range. 3) determine the value required for the fan fs register: example: fan a has a 2500rpm rating: 2500rpm / 60s gives an output of 41.7hz 41.7hz x 2 pulses = 83.4hz the 83.4hz value is out of the 33hz to 66hz decre- ment/increment range. 4) set bits in the fc register to divide the signal down within the 33hz to 66hz range. bits 1, 0 = 10 (divide by 2: p = 2): 83.4 / 2 = 41.7hz 5) set the fs register to yield approximately 42hz: 42 = 8415 / fs (value) fs (value) = 200 fs register = 11001000 6) in current-sense feedback, a current pulse is gener- ated whenever there is a step increase in fan cur- rent. the frequency of pulses is then not only determined by the fan rpms and the number of poles, but also by the update rate at which the fan driver forces an increase in voltage across the fan. the maximum current pulse frequency is then given by: f c = f ? p / (p-1) where f = {rpm/60} ? poles and p is the value in fcd. the value required for the fan fs register is: fs = 8415 / {f / (p-1)} the fan speed limit in fctl should be set to: f l = 8415 / (n ? f c ) a value of p = 1 cannot be used in current-sense mode. fan selection for closed-loop operation and fan monitoring, the MAX6660 requires fans with tachometer outputs. a tachometer output is typically specified as an option on many fan models from a variety of manufacturers. verify fs f p = ? ? ? ? ? ? 8415 f rpm x poles = ? ? ? ? ? ? 60
MAX6660 remote-junction temperature-controlled fan-speed regulator with smbus interface 20 ______________________________________________________________________________________ the nature of the tachometer output (open collector, totem pole) and the resultant levels and configure the connection to the MAX6660. for a fan with an open drain/collector output, a pullup resistor of typically 5k ? must be connected between fan and vfan. note how many pulses per revolution are generated by the tachometer output (this varies from model to model and among manufacturers, though two pulses per revolu- tion is the most common). table 14 lists the representa- tive fan manufacturers and the model they make available with tachometer outputs. low-speed operation brushless dc fans increase reliability by replacing mechanical commutation with electronic commutation. by lowering the voltage across the fan to reduce its speed, the MAX6660 is also lowering the supply volt- age for the electronic commutation and tachometer electronics. if the voltage supplied to the fan is lowered too far, the internal electronics may no longer function properly. some of the following symptoms are possible: the fan may stop spinning. the tachometer output may stop generating a signal. the tachometer output may generate more than two pulses per revolution. the problems that occur and the supply voltages at which they occur depend on which fan is used. as a rule of thumb, 12v fans can be expected to expe- rience problems somewhere around 1/4 and 1/2 their rated speed. chip information transistor count: 22,142 process: bicmos table 14. fan manufacturers manufacturer fan model option comair roton all dc brushless models can be ordered with optional tachometer output. ebm-papst tachometer output optional on some models. nmb all dc brushless models can be ordered with optional tachometer output. panasonic panaflo and flat unidirectional miniature fans can be ordered with tachometer output. sunon tachometer output optional on some models. 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 vfan tach in stby smbclk gain smbdata alert addo overt top view MAX6660 qsop v cc dxp add1 dxn fan pgnd agnd pin configuration
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 ____________________ 21 ? 2001 maxim integrated products printed usa is a registered trademark of maxim integrated products. remote-junction temperature-controlled fan-speed regulator with smbus interface MAX6660 package information qsop.eps

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Price & Availability of MAX6660

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