LM88 Factory Programmable Dual Remote-Diode Thermostat General Description Features The LM88 is a dual remote-diode temperature sensor with 3 digital comparators. The LM88 has 3 open-drain outputs (O_SP0, O_SP1 and O_CRIT) that can be used as interrupts or to signal system shutdown. The digital comparators can be factory programmed to make a greater than or less than comparison. When programmed for a greater than comparison outputs: O_SP0 and O_SP1 activate when the temperatures measured by D0 or D1 exceed the associated setpoints of T_SP0 or T_SP1. O_CRIT activates when the temperature measured by either D0 or D1 exceeds setpoint T_CRIT. T_CRIT can be set at 1˚C intervals from −40˚C to +125˚C. T_SP0 and T_SP1 can be set at 4˚C intervals in the range of T_CRIT +127˚C/−128˚C. Hysteresis for all comparators is set to 1˚C. O_CRIT, in conjunction with T_CRIT, could be used to prevent catastrophic damage to key subsystems such as notebook Card Bus cards while O_SP0 and O_SP1, in conjunction with T_SP0 and T_SP1, can warn of an impending failure. The LM88 is available in an 8-lead mini-small-outline package. n 2 external remote diode input channels n 3 digital comparator outputs, 1 per remote diode and one T_CRIT common to both n Factory programmable greater than or less than comparisons n 1˚C comparator hysteresis n 2 setpoints, T_SP0 and T_SP1, factory programmable in 4˚C intervals n 1 setpoint, T_CRIT, factory programmable in 1˚C intervals n Active Low open-drain digital outputs n 8-pin mini-SO plastic package Applications n n n n n n n n Key Specifications j Power Supply Voltage 1.5 mA (max) j LM88 Temperature Range j Diode Setpoint Temperature Range j −40˚C to +85˚C 0˚C to +125˚C Temperature Trip Point Accuracy: Diode Junction Temperature (TDJ) Microprocessor Thermal Management Appliances Portable Battery Powered Systems Fan Control Industrial Process Control HVAC Systems Remote Temperature Sensing Electronic System Protection 2.8V–3.8V j Power Supply Current +45˚C to +85˚C +60˚C to +100˚C LM88CIM Accuracy LM88CIM Temperature Range ± 3˚C (max) ± 3˚C (max) −40˚C to +85˚C −40˚C to +85˚C Note: These are sample ranges. Contact factory for other ranges. Simplified Block Diagram and Connection Diagram MSOP-8/MUA08A Package 10132601 Top View © 2001 National Semiconductor Corporation 10132602 For simplicity, the effects of the hysteresis are not shown in the temperature response diagram. DS101326 www.national.com LM88 Factory Programmable Dual Remote-Diode Thermostat August 2001 LM88 Simplified Block Diagram and Connection Diagram Order Number Device Marking NS Package Number Transport Media T08A MUA08A or MSOP-8 Tape and Real T08A MUA08A or MSOP-8 LM88CIMM-A LM88CIMMX-A LM88CIMM-B LM88CIMMX-B (Continued) T_SP0 (˚C) T_SP1 (˚C) T_CRIT (˚C) S etpoint Accuracy (˚C) 61 49 80 ±3 41 49 60 ±3 Rail Rail Tape and Real For other setpoints please contact the factory. Performance is dependent on temperature range. Typical Application 10132613 FIGURE 1. Thermal Protection for Pentium ® Processor and Graphics Chip www.national.com 2 Operating Ratings(Note 1) (Note 1) Input Voltage 6V Input Current at any pin (Note 2) 5mA Package Input Current (Note 2) 20mA LM88 Absolute Maximum Ratings Operating Temperature Range TMIN ≤ T ≤ TMAX −40˚C ≤ TA ≤ +85˚C LM88CIMM 0˚C ≤ TDJ ≤ +125˚C Remote Diode Junction Package Dissipation at TA = 25˚C (Note 4) + Positive Supply Voltage (V ) 900mW Maximum V O_CRIT, V and V O_SP1 Soldering Information MSOP Package (Note 6) : Vapor Phase (60 seconds) +2.8V to +3.8V O_SP0 +5.5V 215˚C Infrared (15 seconds) 220˚C Storage Temperature −65˚C to + 150˚C ESD Susceptibility (Note 5) Human Body Model Machine Model 2500V 250V LM88 Electrical Characteristics The following specifications apply for 2.8VDC≤V+ ≤ 3.8VDC unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C unless otherwise specified. Symbol Parameter Conditions Typical LM88CIMM Units (Note 7) Limits (Limits) (Note 8) Temperature Sensor Setpoint Temperature Accuracy (Note 9) +60˚C ≤ TDJ ≤ +100˚C ±3 ˚C (max) +45˚C ≤ TDJ ≤ +85˚C +30˚C ≤ TDJ ≤ +70˚C Setpoint Hysteresis Output Update Rate 1 ˚C (min) 1 ˚C (max) 920 ms (max) 210 µA (max) 46 µA (min) 21 µA (max) 4.6 µA (min) VD−, VD0 and VD1 Analog Inputs ID+SOURCE VD−Out Diode Source Current (D+ − D−)=0.65; high level 120 (D+ − D−)=0.65; low level 12 D− Output Source Voltage 0.7 V LM88 Electrical Characteristics The following specifications apply for 2.8VDC≤V+ ≤ 3.8VDC unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C unless otherwise specified. Symbol Parameter Conditions Typical Limits Units (Note 7) (Note 8) (Limits) 1.5 mA (max) 2 µA (max) VOUT =V+ =3.8V to 2.8V 40 µA (max) IOUT = +3 mA 0.4 V (max) V+ Power Supply IS Supply Current Digital Outputs IOUT(“1”) VOUT(“0”) Logical “1” Output Leakage Current (Note 10) Logical “0” Output Voltage VOUT =V+− 0.6V where V+ =3.8V to 2.8V Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. 3 www.national.com LM88 LM88 Electrical Characteristics (Continued) Note 2: When the input voltage (VI) at any pin exceeds the power supply (VI < GND or VI > V+), the current at that pin should be limited to 5mA. The 20mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5mA to four. Note 3: Parasitics or ESD protection circuitry are shown in the diagram found below. The ESD Clamp circtuitry is triggered on when there is an ESD event. The table maps what devices appear on the different pins. Pin Name D1 D2 D3 D4 D0+ X X X X D5 D6 R1 X 50Ω D− X X X X D1+ X X X X X 50Ω X 50Ω O_CRIT X X X X 0Ω O_SP1 X X X X 0Ω O_SP0 X X X X 0Ω X 10132604 Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature), θJA (junction to ambient thermal resistance) and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PD = (TJmax–TA)/θJA or the number given in the Absolute Maximum Ratings, whichever is lower. For this device, TJmax = 125˚C. For this device the typical thermal resistance (θJA) of the different package types when board mounted follow: Package Type θJA MUA08A 250˚C/W Note 5: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly into each pin. Note 6: See the URL ”http://www.national.com/packaging/“ for other recomdations and methods of soldering surface mount devices. Note 7: Typicals are at TJ = TA = 25˚C and represent most likely parametric norm. Note 8: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 9: These are sample temperature ranges, contact the factory for other temperature ranges. Performance is dependent on temperature range. Note 10: The two IOH specifications are intended to describe two operating regions of the output voltage. In Region 1, V+− 0.6V and below, there is normal leakage current, 2µA (max). In Region 2, V+− 0.6V to V+, there is additional current flowing caused by the ESD protection circuitry (see Figure in Note 3). The maximum current flow is under short circuit conditions as specified at 40µA (max). Under normal operating conditions a pull-resistor (R) will be used. The voltage drop across this pull-up resistor caused by the 2µA normal leakage current with large values of R (much greater than 100k) will bias diode D1 into the cutoff region causing the additional current to be negligible in the voltage drop calculation. With low values of R more current will flow as in the case of a 1.1k pull-up, 20µA may flow causing less than 22mV of voltage drop. www.national.com 4 LM88 1.0 Functional Description 10132611 a) When programmed for a greater than comparison 10132612 b) When programmed for a less than comparison FIGURE 2. Comparator output temperature response diagrams dition, to T_CRIT ± 1˚C is false. The CRIT comparator can be factory programmed to make a greater than or less than comparison. (See Section 1.3 LM88 OPTIONS) 1.1 PIN DESCRIPTIONS V+ This is the positive supply voltage pin, which has a range of 2.8 to 3.8 volts. This pin should be bypassed with a 0.1µF capacitor to ground. GND This is the ground pin. D0+, D1+ These pins connect to the positive terminal of the diodes (e.g. a 2N3904 collector base shorted or a Pentium thermal diode anode) and provide the source current for forward biasing the diodes for the temperature measurement. During a temperature conversion, the current source switches between 120µA and 12µA. The diodes are sampled sequentially. D− This pin should be connected to the negative pin of each diode (e.g. a 2N3904 emitter or a Pentium thermal diode cathode). A star connection is recommended. Separate traces should be routed from this pin to each diode cathode. This pin biases the negative diode terminals to approximately 0.7V. O_CRIT This is an active-low open-drain digital output. It goes LOW when a comparison of either diode temperature reading to the setpoint T_CRIT is true. It returns to HIGH when the comparison of the diode temperature, that caused the true con- 5 O_SP1 This is an active-low open-drain digital output. It goes LOW when the comparison of the temperature reading of diode one to the value of T_SP1 is true. The SP1 comparator has a built in hysteresis of 1˚C. Therefore, O_SP1 returns to HIGH when diode one’s temperature comparison to the value of T_SP1 ± 1˚C is false. The SP1 comparator can be factory programmed to make a greater than or less than comparison.(See Section 1.3 LM88 OPTIONS) O_SP0 This is an active-low open-drain digital output. It goes LOW when the comparison of the temperature reading of diode one to the value of T_SP0 is true. The SP0 comparator has a built in hysteresis of 1˚C. Therefore, O_SP0 returns to HIGH when diode one’s temperature comparison to the value of T_SP0 ± 1˚C is false. The SP0 comparator can be factory programmed to make a greater than or less than comparison.(See Section 1.3 LM88 OPTIONS) www.national.com LM88 1.0 Functional Description (Continued) 1.2 TYPICAL PIN CONNECTION Pin Label Pin Number Typical Connection D0+ 1 3904-type transistor shorted-collector base or Pentium thermal diode anode; 2.2nF capacitor connected to D- D− 2 3904-type transistor emitter or Pentium thermal diode cathode (individual traces are required to each diode; do not daisy chain); two 2.2nF capacitors connected to D0+ and D1+ D1+ 3 3904-type transistor shorted collector-base or Pentium thermal diode anode; 2.2nF capacitor connected to D- GND 4 a quiet system ground O_CRIT 5 2k pull-up; system shutdown or the THERM pin of the ICH (I/O Controller Hub found in PCs) O_SP1 6 2k pull-up; general purpose input (GPI), to determine which diode caused the THERM event O_SP1 7 2k pull-up; general purpose input (GPI), to determine which diode caused the THERM event V+ 8 3.3V; 0.1µF bypass capacitor be greater than or less than. All CRIT comparisons are required to be the same, either greater than or less than. The comparator hysteresis can also be factory set to one, two or three degrees. The hysteresis for all comparisons is required to be the same. 1.3 LM88 OPTIONS 1.3.1 Set-Point Values T_SP0 and T_SP1 are dependent on the value of T_CRIT: T_SP0 = T_CRIT + 4a + 1 T_SP1 = T_CRIT + 4b + 1 where: a and b are any integer in the range of −32 to +31. T_CRIT can be any value in the range of 0˚C to +125˚C with a resolution of 1˚C. 2.0 Application Hints 2.1 OPEN-DRAIN OUTPUTS The O_SP0, O_SP1 and 0_CRIT outputs are open-drain outputs and do not have internal pull-ups. A “high” level will not be observed on these pins until pull-up current is provided from some external source, typically a pull-up resistor. Choice of resistor value depends on many system factors but, in general, the pull-up resistor should be as large as possible. This will minimize any internal temperature reading errors due to internal heating of the LM88. The maximum resistance of the pull-up needed to provide a 2.1V high level, based on LM88 specification for High Level Output Current with the supply voltage at 3.0V, is 430kΩ. 1.3.2 Functionality The LM88’s comparators can be factory programmed to do a greater than or less than comparison. When programmed for a greater than comparison, the comparison result is true when the temperature measured is above the preprogrammed setpoint temperature. The comparison returns to false when the temperature measured is below or equal to the setpoint temperature minus one degree. For a less than comparison the comparison result is true when the temperature measured is below the preprogrammed limit. The result turns to false when the temperature measured is above or equal to the setpoint limit plus one degree. SP0, SP1 and CRIT comparisons can all be independently programmed to www.national.com 2.2 THERMAL DIODE MOUNTING CONSIDERATIONS To measure temperature the LM88 uses two remote diodes. These diodes can be located on the die of a target IC, allowing measurement of the IC’s temperature, independent 6 temperature sensor. The only other parameter is η, which depends on the diode that is used for measurement. Since ∆VBE is proportional to both η and T, the variations in η cannot be distinguished from variations in temperature. Since the non-ideality factor is not controlled by the temperature sensor, it will directly add to the inaccuracy of the sensor. For the Pentium II, Intel specifies a ± 1% variation in η from part to part. As an example, assume a temperature sensor has an accuracy specification of ± 3 ˚C at room temperature of 25 ˚C and the process used to manufacture the diode has a non-ideality variation of ± 1%. The resulting accuracy of the temperature sensor at room temperature will be: TACC = ± 3˚C + ( ± 1% of 298 ˚K) = ± 6˚C (Continued) of the LM88’s temperature. The LM88 has been optimized to measure the remote diode of a Pentium type processor as shown in Figure 3. A discrete diode can also be used to sense the temperature of external objects or ambient air. Remember that a discrete diode’s temperature will be affected, and often dominated, by the temperature of its leads. As with any IC, the LM88 and accompanying wiring and circuits must be kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit may operate at cold temperatures where condensation can occur. Printed-circuit coatings and varnishes such as Humiseal and epoxy paints or dips are often used to ensure that moisture cannot corrode the LM88 or its connections. Moisture may also cause leakage on the diode wiring and therefore affect the accuracy of the temperature set-points. . The additional inaccuracy in the temperature measurement caused by η can be eliminated if each temperature sensor is calibrated with the remote diode that it will be paired with. 2.4 PCB LAYOUT to MINIMIZE NOISE In a noisy environment, such as a processor motherboard, layout considerations are very critical. Noise induced on traces running between the remote temperature diode sensor and the LM88 can cause temperature conversion errors. The following guidelines should be followed: 1. Place a 0.1 µF power supply bypass capacitor as close as possible to the VDD pin and the recommended 2.2 nF capacitor as close as possible to the D+ and D− pins. Make sure the traces to the two 2.2nF capacitor are matched. 2. The recommended 2.2nF diode bypass capacitor actually has a range of 200pF to 3.3nF. The average temperature accuracy will not change over that capacitance range. Increasing the capacitance will lower the corner frequency where differential noise error will start to affect the temperature reading thus producing a reading that is more stable. Conversely, lowering the capacitance will increase the corner frequency where differential noise error starts to affect the temperature reading thus producing a reading that is less stable. 3. Ideally, the LM88 should be placed within 10cm of the remote diode pins with the traces being as straight, short and identical as possible. Trace resistance of 1Ω can cause as much as 1˚C of error. This error can be compensated by using the Remote Temperature Offset Registers, since the value placed in these registers will automatically be subtracted or added to the remote temperature reading. 4. Diode traces should be surrounded by a GND guard ring to either side, above and below if possible. This GND guard should not go between the D+ and D− lines so that in the event that noise does couple to the diode lines, it would be coupled common mode and rejected.(See Figure 4) 5. Avoid routing diode traces in close proximity to power supply switching or filtering inductors. 6. Avoid running diode traces close to or parallel to high speed digital and bus lines. Diode traces should be kept at least 2cm apart from the high speed digital traces. 7. If it is necessary to cross high speed digital traces, the diode traces and the high speed digital traces should cross at a 90 degree angle. 10132615 FIGURE 3. Pentium or 3904 Temperature vs LM88 Temperature Set-point Most silicon diodes do not lend themselves well to this application. It is recommended that a 2N3904 transistor base emitter junction be used with the collector tied to the base. A diode connected 2N3904 approximates the junction available on a Pentium III microprocessor for temperature measurement. Therefore, the LM88 can sense the temperature of this diode effectively. 2.3 EFFECTS OF THE DIODE NON-IDEALITY FACTOR ON ACCURACY The technique used in today’s remote temperature sensors is to measure the change in VBE at two different operating points of a diode. For a bias current ratio of N:1, this difference is given as: where: — η is the non-ideality factor of the process the diode is manufactured on, — q is the electron charge, — k is the Boltzmann’s constant, — N is the current ratio, — T is the absolute temperature in ˚K. The temperature sensor then measures ∆VBE and converts to IT digital data. In this equation, k and q are well defined universal constants, and N is a parameter controlled by the 7 www.national.com LM88 2.0 Application Hints LM88 2.0 Application Hints as much as 1˚C of error in the diode temperature reading. Keeping the printed circuit board as clean as possible will minimize leakage current. (Continued) 8. The ideal place to connect the LM88’s GND pin is as close as possible to the processor GND associated with the sense diode. 9. Leakage current between D+ and GND should be kept to a minimum. One nano-ampere of leakage can cause 10132633 FIGURE 4. Ideal Diode Trace Layout 3.0 Applications Circuits 10132614 FIGURE 5. Pentium processor Thermal Management with Fan Control 10132603 FIGURE 6. Card Bus Thermal Management www.national.com 8 LM88 Factory Programmable Dual Remote-Diode Thermostat Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead Molded Mini Small Outline Package (MSOP) (JEDEC REGISTRATION NUMBER M0-187) Order Number LM88CIMM, or LM88CIMMX NS Package Number MUA08A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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