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LTC2997 1 2997fa typical application features description remote/internal temperature sensor the ltc ? 2997 is a high-accuracy analog output temperature sensor. it converts the temperature of an external sensor or its own temperature to an analog voltage output. a built-in algorithm eliminates errors due to series resistance be- tween the LTC2997 and the sensor diode. the LTC2997 gives accurate results with low-cost diode- connected npn or pnp transistors or with integrated temperature transistors on microprocessors or fpgas. tying pin d + to v cc configures the LTC2997 to measure its internal temperature. the LTC2997 provides an additional 1.8v reference voltage output which can be used as an adc reference input or for generating temperature threshold voltages to compare against the v ptat output. the LTC2997 provides a precise and versatile micropower solution for accurate temperature sensing. single remote temperature sensor applications n converts remote sensor or internal diode temperature to analog voltage n 1c remote temperature accuracy n 1.5c internal temperature accuracy n built-in series resistance cancellation n 2.5v to 5.5v supply voltage n 1.8v reference voltage output n 3.5ms v ptat update time n 4mv/k output gain n 170a quiescent current n available in 6-pin 2mm 3mm dfn package n temperature measurement n remote temperature measurement n environmental monitoring n system thermal control n desktop and notebook computers n network servers l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. v ptat vs remote sensor temperature v ref 4mv/k 1.8v 2.5v to 5.5v 0.1f d + d C LTC2997 mmbt 3904 470pf 2997 ta01a v cc v ptat gnd remote sensor temperature (c) C50 0.8 v ptat (v) 1.0 1.2 1.4 050 100 150 2997 ta01b 1.6 1.8 C25 25 75 125
LTC2997 2 2997fa pin configuration terminal voltages v cc ........................................................... C0.3v to 6v d + , d C , v ptat , v ref ......................C0.3v to v cc + 0.3v top view v ref gnd v cc d + d C v ptat dcb package 6-lead (2mm w 3mm) plastic dfn 4 5 7 6 3 2 1 t jmax = 150c, ja = 64c/w exposed pad pcb ground connection optional order information operating ambient temperature range LTC2997c ................................................ 0c to 70c LTC2997i ............................................. C40c to 85c LTC2997h .......................................... C40c to 125c storage temperature range .................. C65c to 150c lead free finish tape and reel (mini) tape and reel part marking* package description temperature range LTC2997cdcb#trmpbf LTC2997cdcb#trpbf lfqz 6-lead (2mm 3mm) plastic dfn 0c to 70c LTC2997idcb#trmpbf LTC2997idcb#trpbf lfqz 6-lead (2mm 3mm) plastic dfn C40c to 85c LTC2997hdcb#trmpbf LTC2997hdcb#trpbf lfqz 6-lead (2mm 3mm) plastic dfn C40c to 125c trm = 500 pieces. *temperature grades are identified by a label on the shipping container. consult ltc marketing for parts specified with wider operating temperature ranges. consult ltc marketing for information on lead based finish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ absolute maximum ratings (notes 1, 2)
LTC2997 3 2997fa electrical characteristics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: all currents into pins are positive; all voltages are referenced to gnd unless otherwise noted. symbol parameter conditions min typ max units v cc supply voltage l 2.5 3.3 5.5 v uvlo supply undervoltage lockout threshold v cc falling l 1.7 1.9 2.1 v i cc average supply current l 120 170 250 a temperature monitoring v ref reference voltage LTC2997 LTC2997c LTC2997i LTC2997h l l l 1.797 1.793 1.790 1.787 1.8 1.8 1.8 1.8 1.803 1.804 1.807 1.808 v v v v v ref load regulation error i load = 200a; v cc = 3.3v l 1.5 mv remote sense current C8 C192 a diode select threshold (note 3) l v cc C 600 v cc C 300 v cc C 100 mv t update temperature update interval 3.5 5 ms k t v ptat slope = 1.004 (note 4) 4 mv/k v ptat load regulation i load = 200a; v cc = 3.3v (note 7) 1.5 mv t int internal temperature error LTC2997c, LTC2997i LTC2997h l l 0.5 1.5 2 c c t rmt remote temperature error, = 1.004 0c to 100c (notes 5, 7) C40c to 0c (notes 5, 7) 100c to 125c (notes 5, 7) 0.25 0.25 1 1.5 1.5 c c c t vcc temperature error vs supply 2.5v v cc 5.5v l 0 .1 1 c/v t rs series resistance cancellation error r series = 100 l 0.25 1 c temperature noise (note 6) 0.25 0.015 c rms c/ hz the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c, v cc = 3.3v, unless otherwise noted. note 3: if voltage on pin d + exceeds the diode select threshold the LTC2997 uses the internal diode sensor. note 4: = ideality factor of remote diode note 5: remote diode temperature. note 6: guaranteed by design and not subject to test. note 7: guaranteed by design and test correlation.
LTC2997 4 2997fa typical performance characteristics remote temperature error vs series resistance, t rs remote temperature error vs c decouple (between d + and d C ) temperature error with LTC2997 at same temperature as remote diode remote temperature error vs t a with remote diode at 25c internal temperature error vs t a , t int uvlo vs temperature v cc rising, falling buffered reference voltage vs temperature, v ref series resistor () 0 C1.5 error (c) C1.0 0 C0.5 800 600 2997 g05 0.5 1.5 1.0 200 400 1000 decouple capacitor (nf) 0 error (c) 0 C0.4 C0.8 4 3 2997 g06 0.4 0.8 12 5 averaging time (ms) 0.01 0 v ptat noise (c rms) 0.05 0.15 0.20 0.10 1 100 2997 g07 0.25 0.30 0.1 10 v cc (v) 1 C1.0 error (c) C0.8 C0.2 0 C0.4 C0.6 35 2997 g04 0.2 0.4 24 6 temperature error vs v cc - remote/internal, t vcc v ptat noise vs averaging time t a (c) C50 C3 t rmt error (c) C2 0 C1 75 150 100 2997 g01 3 1 2 C25 0 25 50 125 t a (c) C50 C3 t rmt error (c) C2 0 C1 75 150 100 2997 g02 3 1 2 C25 0 25 50 125 t a (c) C50 C3 t int error (c) C2 0 C1 75 150 100 2997 g03 3 1 2 C25 0 25 50 125 t a (c) C50 1.0 uvlo (v) 1.2 1.8 2.0 1.6 1.4 25 75 175 150 2997 g08 2.2 2.4 0 C25 50 100 125 v cc rising v cc falling t a (c) 1.790 v rfe (v) 1.795 2997 g09 1.800 1.810 1.805 C50 25 75 150 0 C25 50 100 125 t a = 25c, v cc = 3.3v unless otherwise noted.
LTC2997 5 2997fa LTC2997 internal sensor thermal step response typical performance characteristics load regulation of v ptat C voltage vs current supply current vs temperature load regulation of v ref C voltage vs current load current (ma) 1.780 v ref (v) 1.800 1.790 0 2997 g10 1.820 1.810 C4 C2 2 4 v cc = 2.5v v cc = 3.5v v cc = 4.5v v cc = 5.5v time (s) air 0 C50 C25 v ptat (c) 0 100 75 50 25 5 2997 g13 125 LTC2997 connected via 5 inch 30awg wrapping wires 12 3 4 ice water boiling water t a (c) C50 150 supply current (a) 160 190 180 170 50 100 2997 g12 200 C25 0 25 75 125 150 t a = 25c, v cc = 3.3v unless otherwise noted. load current (ma) C4 1.22 v ptat (v) 1.23 1.26 1.25 1.24 C2 0 4 2997 g11 1.27 1.28 2 v cc = 2.5v v cc = 3.5v v cc = 4.5v v cc = 5.5v i leakage (na) C200 C6 t rmt error (c) 4 2 0 C2 C4 0 100 2997 g14 6 C100 200 remote temperature error vs leakage current at d + with remote diode at 25c, t rmt single wire remote temperature error vs potential difference between remote and local ground (vac) frequency (khz) 0.1 0.01 absolute temperature error (c) 1 0.1 10 1000 2997 g15 10 1 100 vac = 50mv p-p
LTC2997 6 2997fa pin functions d + : diode sense current source. d + sources the remote diode sensing current. connect d + to the anode of the re- mote sensor device. it is recommended to connect a 470pf bypass capacitor between d + and d C . larger capacitors may cause settling time errors (see typical performance characteristics). if d + is tied to v cc , the LTC2997 measures the internal sensor temperature. tie d + to v cc if unused. d C : diode sense current sink. connect d C to the cathode of the remote sensor device. tie d C to gnd for single wire remote sensing (see typical applications) or internal temperature sensing. gnd: device ground. v cc : supply voltage. bypass this pin to gnd with a 0.1f (or greater) capacitor. v cc operating range is 2.5v to 5.5v. v ptat : v ptat voltage output. the voltage on this pin is proportional to the sensors absolute temperature. v ptat can drive a capacitive load of up to 1000pf. for larger load capacitance, insert 1k between v ptat and load to guarantee stability. v ptat can drive up to 200a of load current. v ptat is pulled low when the supply voltage goes below the under voltage lockout threshold. v ref : voltage reference output. v ref provides a 1.8v reference voltage. v ref can drive a capacitive load of up to 1000pf. for larger load capacitance, insert 1k between v ref and load to guarantee stability. v ref can drive up to 200a of load current. leave v ref open if unused. exposed pad: exposed pad may be left open or soldered to gnd for better thermal coupling.
LTC2997 7 2997fa block diagram temperature to voltage converter ext/int mux 1.2v v ref gnd v ptat v supply v cc d + d C 300mv 1.8v 600k 1200k 2997 bd C + C + uvlo mux + C internal sensor 3 6 5 2 1 4 external sensor
LTC2997 8 2997fa operation the block diagram shows the main components of the LTC2997. the LTC2997 measures temperature using either a remote or internal diode and provides a buffered voltage propor- tional to absolute temperature (v ptat ) and a buffered 1.8v reference voltage. remote temperature measurements usually use a diode connected transistor as a tempera- ture sensor, allowing the remote sensor to be a discrete npn (ex. mmbt3904) or an embedded pnp device in a microprocessor or fpga. temperature measurements are conducted by measur- ing the diode voltage at multiple test currents. the diode equation can be solved for t, where t is degrees kelvin, i s is a process dependent factor on the order of 10 C13 a, is the diode ideality factor, k is the boltzmann constant and q is the electron charge: t = q ?k ? v diode ln i d i s ? ? ? ? ? ? this equation has a relationship between temperature and voltage, dependent on the process-dependent variable i s . measuring the same diode (with the same value i s ) at two different currents yields an expression which is independent of i s . the value in the natural logarithm term becomes the ratio of the two currents, which is process independent. t = q ?k ? v diode2 Cv diode1 ln i d2 i d1 ? ? ? ? ? ? series resistance cancellation resistance in series with the remote diode causes a positive temperature error by increasing the measured voltage at each test current. the composite voltage equals: v diode + v error = kt q ?ln i d i s ? ? ? ? ? ? + r s ?i d where r s is the series resistance. the LTC2997 removes this error term from the sensor signal by subtracting a cancellation voltage (see figure 1). a resistance extraction circuit uses one additional current (i 3 ) to determine the series resistance in the measurement path. once the correct value of the resistor is determined v cancel equals v error . now the temperature to voltage converter's input signal is free from errors due to series resistance and the sensor temperature can be determined using currents i 1 and i 2 . figure 1. series resistance cancellation v be v be v error r series v ptat v cancel = v error i 3 i 1 , i 2 d + 2997 f01 + C resistance extraction circuit temperature to volt converter d C
LTC2997 9 2997fa power up and uvlo the basic LTC2997 application using an external npn transistor is shown in figure 2. applications information of up to 100 to an error smaller than 1c (see typical performance characteristics). the LTC2997 continuously measures the sensor diode at different test currents and updates v ptat every 3.5ms (typical). input noise filtering the change in sensor voltage per c is hundreds of mi- crovolts, so electrical noise must be kept to a minimum. bypass d+ and dC with a 470pf capacitor close to the LTC2997 to suppress external noise. bypass capacitors greater 1nf cause settling time errors of the different measurement currents. see typical performance char- acteristics. long wires connecting external sensors add series resistance, mutual capacitance between d + and d C , and cause leakage currents. a 10m cat6 cable has ~500pf of mutual capacitance and adds negligible series resistance and leakage currents. recommended shielding and pcb trace considerations for best noise immunity are illustrated in figure 3. the v cc pin must exceed the undervoltage threshold of 1.9v (typical) for normal operation. for v cc below uvlo the LTC2997 enters power-on reset and v ptat is pulled low. temperature measurements before each conversion a voltage comparator connected to d + automatically sets the LTC2997 into external or in- ternal mode. tying d + to v cc enables internal mode and v ptat represents the die temperature. the v ptat gain, k t , is 4mv/k. the temperature in kelvin is easily calculated: t kelvin = v ptat k t for v d + more than 300mv below v cc (typical) the LTC2997 assumes that an external sensor is connected and will start sending sensing currents to the remote sensor diode. the anode of the external sensor must be connected to pin d + . the cathode should be connected to d C for best external noise immunity. for single wire measurements the sen- sor cathode is connected to remote gnd and d C must be connected to local gnd (see figure 7). small ground dc voltages (<200mv) between the two cathode potentials do not impact the measurement accuracy. ac voltages at odd multiples of 6khz (20%) cause temperature measure- ment errors (see typical performance characteristics). the LTC2997 is calibrated to yield a v ptat gain of 4mv/k for a remote diode with an ideality factor of 1.004. a built-in algorithm cancels errors due to series resistance figure 2. basic application circuit output noise filtering the v ptat output typically exhibits 1mv rms (0.25c rms) noise. for applications which require lower noise digital or analog averaging can be applied to the output. choose the averaging time according to the following equation: t avg = 0.01 5 c/ hz t noise ? ? ? ? ? ? 2 [] where t avg is the averaging time and t noise the desired temperature noise in c rms. for example, if the desired noise performance is 0.015c rms, set the averaging time to one second. see typical performance characteristics. d + d C LTC2997 2997 f03 gnd 470pf gnd shield trace npn sensor figure 3. recommended pcb layout v ref 2.5v to 5.5v d + d C LTC2997 mmbt3904 470pf 2997 f02 v cc v ptat gnd 4mv/k 1.8v 0.1f
LTC2997 10 2997fa choosing a sensor the LTC2997 is factory calibrated for an ideality factor of 1.004, which is typical of the popular mmbt3904 npn transistor. semiconductor purity and wafer-level processing intrinsically limit device-to-device variation, making these devices interchangeable between most manufacturers with a temperature error of typically less than 0.5c. some recommended sources are listed in table 1: table 1. recommended transistors for use as temperature sensors. manufacturer part number package fairchild semiconductor mmbt3904 sot-23 central semiconductor cmpt3904 sot-23 diodes, inc. mmbt3904 sot-23 on semiconductor mmbt3904lt1 sot-23 nxp mmbt3904 sot-23 infineon mmbt3904 sot-23 rohm umt3904 sc-70 discrete two terminal diodes usually have ideality factors significantly higher than 1.004 and are therefor not recom- mended as remote sensing devices. protection the LTC2997 can withstand up to 4kv of electrostatic discharge (esd, human body). esd beyond this voltage can damage or degrade the device including lowering the remote sensor measurement accuracy due to increased leakage currents on d + and d C . to protect the sensing inputs against larger esd strikes, external protection can be added using tvs diodes to ground (figure 4). care must be taken to choose diodes with low capacitance and low leakage currents in order not to degrade the external sensor measurement accuracy (see typical performance characteristics). applications information ideality factor scaling while an ideality factor value of 1.004 is typical of many sensor devices, small deviations can yield significant tem- perature errors. the ideality factor acts as a temperature scaling factor. the temperature error for a 1% deviation is 1% of the kelvin temperature. thus, at 25c (298k) a +1% accurate ideality factor error yields a +2.98 degree error. at 85c (358k) a +1% error yields a 3.58 degree error. it is possible to scale the ptat voltage if an external sensor with an ideality factor other than 1.004 is used. the scaling equation for the compensated ptat voltage is listed below. LTC2997 ideality calibration value: cal = 1.004 actual remote sensor ideality value: act compensated ptat voltage: v ptat _comp = cal act ?v ptat _meas compensated kelvin temperature: t kelvin_comp = cal act ?t kelvin_meas compensated celsius temperature: t celsius _comp = cal act ?(t kelvin_meas ) C 273.15 figure 4. increasing esd robustness with tvs diodes d + d C LTC2997 mmbt3904 pesd5z6.0 220pf 10 10 2997 f04 gnd
LTC2997 11 2997fa typical applications figure 6. internal temperature sensor figure 7. remote cpu temperature sensor figure 5. single remote temperature sensor v ref 4mv/k 1.8v 2.5v to 5.5v 0.1f d + d C LTC2997 mmbt3904 470pf 2997 f05 v cc v ptat gnd v ref 2.5v to 5.5v d + d C LTC2997 c 2997 f06 v cc v ptat gnd 0.1f a/d 4mv/k 1.8v v ref 2.5v to 5.5v d + d C LTC2997 cpu/ fpga/ asic 470pf 2997 f07 v cc v ptat gnd 0.1f 4mv/k 1.8v
LTC2997 12 2997fa typical applications figure 10. long distance remote temperature sensor figure 9. output noise filter 2.5v to 5.5v d + d C LTC2997 2997 f09 v cc v ptat v ptat(filter) >1k gnd 0.1f c filter rc time constant (ms) 0.005 0 v ptat noise (c rms) 0.05 0.15 0.20 0.10 0.5 50 0.25 0.30 0.05 5 figure 8. single wire remote temperature sensor v ref 2.5v to 5.5v d + d C LTC2997 470pf 2n3904 2997 f08 v cc v ptat gnd 0.1f 4mv/k 1.8v v ref 2.5v to 5.5v d + d C LTC2997 cat6 stp cable 10m maximum 470pf mmbt 3904 2997 f10 v cc v ptat gnd 0.1f 4mv/k 1.8v
LTC2997 13 2997fa typical applications figure 11. analog pwm heater controller figure 12. 75c analog heater controller 5v d + d C LTC2997 v cc v ptat v ref v target v ref gnd 0.1f 470pf 2997 f11 22k 1k 100k 100k 1m 5v 100f measure temperature and set target temperature with resistive divider integrate temperature error pwm oscillator 100pf 10m 10m 10 r heater cet 3904 200k zxm64po35 75k C + C + ltc6079 ltc6079 5v d + d C LTC2997 v cc v ptat v ref gnd 0.1f 470pf 2997 f12 22k v target = 1.3917v 10 r heater irf3708 cet 3904 75k C + ltc6079 4mv/k 1.8v
LTC2997 14 2997fa figure 14. temperature proportional pwm fan speed controller typical applications d + d C LTC2997 v cc v ref v ptat gnd 2997 f14 10k C + ltc6078 470pf mmbt 3904 39k 390k 68k 0.1f 5v mod set ltc6692 v cc out b6015l12f irf3708 12v div gnd fan figure 13. remote diode sensor insensitive to cable connection polarity v ref 2.5v to 5.5v d + d C LTC2997 470pf mmbt3904 2997 f13 v cc v ptat gnd 0.1f 4mv/k 1.8v
LTC2997 15 2997fa figure 15. celsius thermometer figure 16. fahrenheit thermometer typical applications d + d C LTC2997 v cc v ref v ptat 143k gnd 2997 f15 1k 62k 150k 1.8k 1f 0.1f 10mv/c 0v at 0c 1.8v 4mv/k 0.1f 2.5v to 5.5v 100k 5v C5v C + ltc1150 7 4 1 5v d + d C LTC2997 v cc v ref v ptat 270k gnd 2997 f16 62k 255k C5v C + ltc1150 1f 0.1f 10mv/f 0v at 0f 1.8v 4mv/k 0.1f 2.5v to 5.5v 100k 7 4 1
LTC2997 16 2997fa information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. 3.00 0.10 (2 sides) 2.00 0.10 (2 sides) note: 1. drawing to be made a jedec package outline m0-229 variation of (tbd) 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 0.10 bottom view?xposed pad 1.65 0.10 (2 sides) 0.75 0.05 r = 0.115 typ r = 0.05 typ 1.35 0.10 (2 sides) 1 3 6 4 pin 1 bar top mark (see note 6) 0.200 ref 0.00 ?0.05 (dcb6) dfn 0405 0.25 0.05 0.50 bsc pin 1 notch r0.20 or 0.25 45 chamfer 0.25 0.05 1.35 0.05 (2 sides) recommended solder pad pitch and dimensions 1.65 0.05 (2 sides) 2.15 0.05 0.70 0.05 3.55 0.05 package outline 0.50 bsc dcb package 6-lead plastic dfn (2mm 3mm) (reference ltc dwg # 05-08-1715 rev a) package description please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
LTC2997 17 2997fa revision history rev date description page number a 9/11 changed 4mv/c to 4mv/k in features updated description updated electrical characteristics added graph g15 updated pin functions updated applications information updated figures 9, 10, 13, 15, 16 updated related parts 1 1 3 5 6 9, 10 12, 14, 15 18
LTC2997 18 2997fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2011 lt 0911 rev a ? printed in usa related parts typical application part number description comments ltc2990 remote/internal temperature, voltage and current monitor measures two remote diode temperatures, 1c accuracy, 0.06c resolution, 2c internal temperature sensor, i 2 c interface, ltc2909 precision triple/dual input uv, ov and negative voltage monitor two adjustable inputs, 1.5% accuracy, 6.5v shunt regulator ltc2919 precision triple/dual input uv, ov and negative voltage monitor two adjustable inputs, 1.5% accuracy, 6.5v shunt regulator, open-drain/rst, out1 and out2 outputs ltc6078 ltc6078 micropower precision, dual/quad cmos rail-to-rail input/output amplifiers maximum offset voltage of 25v (25c), maximum offset drift of 0.7v/c, maximum input bias of 1pa (25c) to 50pa (85c) ltc6079 micropower precision, dual/quad cmos rail-to-rail input/output amplifiers maximum offset voltage of 25v (25c), maximum offset drift of 0.7v/c, maximum input bias of 1pa (25c) to 50pa (85c) figure 17. thermocouple thermometer with cold junction compensation 5v d + d C LTC2997 v cc v ref v ptat gnd 0.1f 2997 f17 1.3k 5v type k thermocouple out = 4mv/k 127k 5.6pf 10k C + ltc6078

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