LM56 Dual Output Low Power Thermostat General Description Features The LM56 is a precision low power thermostat. Two stable temperature trip points (VT1 and VT2) are generated by dividing down the LM56 1.250V bandgap voltage reference using 3 external resistors. The LM56 has two digital outputs. OUT1 goes LOW when the temperature exceeds T1 and goes HIGH when the the temperature goes below (T1–THYST). Similarly, OUT2 goes LOW when the temperature exceeds T2 and goes HIGH when the temperature goes below (T2–THYST). THYST is an internally set 5˚C typical hysteresis. n n n n n Digital outputs support TTL logic levels Internal temperature sensor 2 internal comparators with hysteresis Internal voltage reference Available in 8-pin SO and Mini-SO8 plastic packages Key Specifications The LM56 is available in an 8-lead Mini-SO8 surface mount package and an 8-lead small outline package. j Power Supply Voltage 2.7V–10V j Power Supply Current 230 µA (max) 1.250V ± 1% (max) j VREF j Hysteresis Temperature Applications n n n n n n n n 5˚C j Internal Temperature Sensor Output Voltage: Microprocessor Thermal Management Appliances Portable Battery Powered 3.0V or 5V Systems Fan Control Industrial Process Control HVAC Systems Remote Temperature Sensing Electronic System Protection (+6.20 mV/˚C x T) + 395 mV n Temperature Trip Point Accuracy: +25˚C +25˚C to +85˚C −40˚C to +125˚C LM56BIM LM56CIM ± 2˚C (max) ± 2˚C (max) ± 3˚C (max) ± 3˚C (max) ± 3˚C (max) ± 4˚C (max) Simplified Block Diagram and Connection Diagram 01289302 01289301 Order Number NS Package Number Transport Media Package Marking LM56BIM LM56BIMX LM56CIM LM56CIMX LM56BIMM LM56BIMMX LM56CIMM LM56CIMMX M08A M08A M08A M08A MUA08A MUA08A MUA08A MUA08A SOP-8 SOP-8 SOP-8 SOP-8 MSOP-8 MSOP-8 MSOP-8 MSOP-8 1000 Units 3500 Units 1000 Units 3500 Units 2500 Units 2500 Units Rail Tape & Reel Rail Tape & Reel LM56BIM LM56BIM LM56CIM LM56CIM © 2006 National Semiconductor Corporation DS012893 Tape & Reel Tape & Reel Tape & Reel Tape & Reel T02B T02B T02C T02C www.national.com LM56 Dual Output Low Power Thermostat January 2006 LM56 Typical Application 01289303 VT1 = 1.250V x (R1)/(R1 + R2 + R3) VT2 = 1.250V x (R1 + R2)/(R1 + R2 + R3) where: (R1 + R2 + R3) = 27 kΩ and VT1 or T2 = [6.20 mV/˚C x T] + 395 mV therefore: R1 = VT1/(1.25V) x 27 kΩ R2 = (VT2/(1.25V) x 27 kΩ) − R1 R3 = 27 kΩ − R1 − R2 FIGURE 1. Microprocessor Thermal Management www.national.com 2 Input Voltage Operating Ratings(Note 1) 12V Input Current at any pin (Note 2) Operating Temperature Range 5 mA Package Input Current(Note 2) 900 mW ESD Susceptibility (Note 5) Human Body Model - Pin 3 Only: 1000V Machine Model Positive Supply Voltage (V+) +2.7V to +10V Maximum VOUT1 and VOUT2 +10V Soldering process must comply with National Semiconductor’s Reflow Temperature Profile specifications. Refer to www.national.com/packaging.(Note 3) 800V All other pins TMIN ≤ TA ≤ TMAX −40˚C ≤ TA ≤ +125˚C LM56BIM, LM56CIM 20 mA Package Dissipation at TA = 25˚C (Note 4) LM56 Absolute Maximum Ratings (Note 1) 125V Storage Temperature −65˚C to + 150˚C LM56 Electrical Characteristics The following specifications apply for V+ = 2.7 VDC, and VREF load current = 50 µA 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 LM56BIM LM56CIM Units (Note 6) Limits Limits (Limits) (Note 7) (Note 7) ±2 ±2 ±3 ±3 ±3 ±4 3 3 ˚C (min) 6 6 ˚C (max) Temperature Sensor Trip Point Accuracy (Includes VREF, Comparator Offset, and +25˚C ≤ TA ≤ +85˚C Temperature Sensitivity errors) −40˚C ≤ TA ≤ +125˚C Trip Point Hysteresis TA = −40˚C 4 TA = +25˚C 5 TA = +85˚C 6 TA = +125˚C 6 Internal Temperature ˚C (max) ˚C (max) ˚C (max) 3.5 3.5 ˚C (min) 6.5 6.5 ˚C (max) 4.5 4.5 ˚C (min) 7.5 7.5 ˚C (max) 4 4 ˚C (min) 8 8 ˚C (max) +6.20 mV/˚C Sensitivity Temperature Sensitivity Error ±2 ±3 ±3 ±4 ˚C (max) ˚C (max) Output Impedance −1 µA ≤ IL ≤ +40 µA 1500 1500 Ω (max) Line Regulation +3.0V ≤ V ≤ +10V, +25 ˚C ≤ TA ≤ +85 ˚C ± 0.36 ± 0.36 mV/V (max) +3.0V ≤ V+ ≤ +10V, −40 ˚C ≤ TA < 25 ˚C ± 0.61 ± 0.61 mV/V (max) +2.7V ≤ V+ ≤ +3.3V ± 2.3 ± 2.3 mV (max) 300 300 nA (max) + VT1 and VT2 Analog Inputs IBIAS Analog Input Bias Current VIN Analog Input Voltage Range VOS 150 Comparator Offset V+ − 1 V GND V 2 8 8 mV (max) VREF Output VREF VREF Nominal 1.250V VREF Error ∆VREF/∆V+ Line Regulation +3.0V ≤ V+ ≤ +10V 0.13 +2.7V ≤ V ≤ +3.3V 0.15 + ∆VREF/∆IL Load Regulation Sourcing +30 µA ≤ IL ≤ +50 µA 3 V ±1 ± 12.5 ±1 ± 12.5 mV (max) 0.25 0.25 mV/V (max) % (max) 1.1 1.1 mV (max) 0.15 0.15 mV/µA (max) www.national.com LM56 Symbol Parameter Conditions Typical Limits Units (Note 6) (Note 7) (Limits) 230 µA (max) V = +2.7V 230 µA (max) V+ = +5.0V 1 µA (max) 0.4 V (max) V+ Power Supply IS Supply Current V+ = +10V + Digital Outputs IOUT(“1”) Logical “1” Output Leakage Current VOUT(“0”) Logical “0” Output Voltage IOUT = +50 µA 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. 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 5 mA. The 20 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four. Note 3: Reflow temperature profiles are different for lead-free and non-lead-free packages. 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 M08A 110˚C/W MUA08A 250˚C/W Note 5: The human body model is a 100 pF capacitor discharge through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged directly into each pin. Note 6: Typicals are at TJ = TA = 25˚C and represent most likely parametric norm. Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). www.national.com 4 LM56 Typical Performance Characteristics Quiescent Current vs Temperature VREF Output Voltage vs Load Current 01289304 01289305 OUT1 and OUT2 Voltage Levels vs Load Current Trip Point Hysteresis vs Temperature 01289307 01289332 Temperature Sensor Output Voltage vs Temperature Temperature Sensor Output Accuracy vs Temperature 01289308 01289309 5 www.national.com LM56 Typical Performance Characteristics (Continued) Trip Point Accuracy vs Temperature Comparator Bias Current vs Temperature 01289310 01289311 OUT1 and OUT2 Leakage Current vs Temperature VTEMP Output Line Regulation vs Temperature 01289331 01289312 VREF Start-Up Response VTEMP Start-Up Response 01289313 01289314 www.national.com 6 LM56 Functional Description 01289315 Pin Descriptions V+ This is the positive supply voltage pin. This pin should be bypassed with a 0.1 µF capacitor to ground. GND This is the ground pin. VREF This is the 1.250V bandgap voltage reference output pin. In order to maintain trip point accuracy this pin should source a 50 µA load. VTEMP This is the temperature sensor output pin. OUT1 This is an open collector digital output. OUT1 is active LOW. It goes LOW when the temperature is greater than T1 and goes HIGH when the temperature drops below T1– 5˚C. This output is not intended to directly drive a fan motor. OUT2 This is an open collector digital output. OUT2 is active LOW. It goes LOW when the temperature is greater than the T2 set point and goes HIGH when the temperature is less than T2– 5˚C. This output is not intended to directly drive a fan motor. This is the input pin for the temperature trip point VT1 voltage for OUT1. This is the input pin for the low temperature trip point VT2 voltage for OUT2. 01289316 VT1 = 1.250V x (R1)/(R1 + R2 + R3) VT2 = 1.250V x (R1 + R2)/(R1 + R2 + R3) where: (R1 + R2 + R3) = 27 kΩ and VT1 or T2 = [6.20 mV/˚C x T] + 395 mV therefore: R1 = VT1/(1.25V) x 27 kΩ R2 = (VT2/(1.25V) x 27 k)Ω–R1 R3 = 27 kΩ − R1 − R2 7 www.national.com LM56 not include any error introduced by the tolerance of the actual resistors used, nor any error introduced by power supply variation. Application Hints 1.0 LM56 TRIP POINT ACCURACY SPECIFICATION If the resistors have a ± 0.5% tolerance, an additional error of ± 0.4˚C will be introduced. This error will increase to ± 0.8˚C when both external resistors have a ± 1% tolerance. For simplicity the following is an analysis of the trip point accuracy using the single output configuration show in Figure 2 with a set point of 82˚C. Trip Point Error Voltage = VTPE, 2.0 BIAS CURRENT EFFECT ON TRIP POINT ACCURACY Bias current for the comparator inputs is 300 nA (max) each, over the specified temperature range and will not introduce considerable error if the sum of the resistor values are kept to about 27 kΩ as shown in the typical application of Figure 1 . This bias current of one comparator input will not flow if the temperature is well below the trip point level. As the temperature approaches trip point level the bias current will start to flow into the resistor network. When the temperature sensor output is equal to the trip point level the bias current will be 150 nA (max). Once the temperature is well above the trip point level the bias current will be 300 nA (max). Therefore, the first trip point will be affected by 150 nA of bias current. The leakage current is very small when the comparator input transistor of the different pair is off (see Figure 3) . The effect of the bias current on the first trip point can be defined by the following equations: Comparator Offset Error for VT1E Temperature Sensor Error = VTSE Reference Output Error = VRE 01289317 FIGURE 2. Single Output Configuration 1. VTPE = ± VT1E − VTSE + VRE Where: 2. VT1E = ± 8 mV (max) 3. VTSE = (6.20 mV/˚C) x ( ± 3˚C) = ± 18.6 mV 4. VRE = 1.250V x ( ± 0.01) R2/(R1 + R2) Using Equations from page 1 of the datasheet. VT1=1.25VxR2/(R1+R2)=(6.20 mV/˚C)(82˚C) +395 mV Solving for R2/(R1 + R2) = 0.7227 then, 5. VRE = 1.250V x ( ± 0.01) R2/(R1 + R2) = (0.0125) x (0.7227) = ± 9.03 mV The individual errors do not add algebraically because, the odds of all the errors being at their extremes are rare. This is proven by the fact the specification for the trip point accuracy stated in the Electrical Characteristic for the temperature range of −40˚C to +125˚C, for example, is specified at ± 3˚C for the LM56BIM. Note this trip point error specification does www.national.com where IB = 300 nA (the maximum specified error). The effect of the bias current on the second trip point can be defined by the following equations: where IB = 300 nA (the maximum specified error). The closer the two trip points are to each other the more significant the error is. Worst case would be when VT1 = VT2 = VREF/2. 8 LM56 Application Hints (Continued) 01289318 FIGURE 3. Simplified Schematic 3.0 MOUNTING CONSIDERATIONS The majority of the temperature that the LM56 is measuring is the temperature of its leads. Therefore, when the LM56 is placed on a printed circuit board, it is not sensing the temperature of the ambient air. It is actually sensing the temperature difference of the air and the lands and printed circuit board that the leads are attached to. The most accurate temperature sensing is obtained when the ambient temperature is equivalent to the LM56’s lead temperature. As with any IC, the LM56 and accompanying wiring and circuits must be kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit operates at cold temperatures where condensation can occur. Printed-circuit coatings are often used to ensure that moisture cannot corrode the LM56 or its connections. 9 www.national.com LM56 Application Hints (Continued) 4.0 VREF AND VTEMP CAPACITIVE LOADING 01289319 FIGURE 4. Loading of VREF and VTEMP The LM56 VREF and VTEMP outputs handle capacitive loading well. Without any special precautions, these outputs can drive any capacitive load as shown in Figure 4 . 6.0 APPLICATIONS CIRCUITS 5.0 NOISY ENVIRONMENTS Over the specified temperature range the LM56 VTEMPoutput has a maximum output impedance of 1500Ω. In an extremely noisy environment it may be necessary to add some filtering to minimize noise pickup. It is recommended that 0.1 µF be added from V+ to GND to bypass the power supply voltage, as shown in Figure 4 . In a noisy environment it may be necessary to add a capacitor from the VTEMP output to ground. A 1 µF output capacitor with the 1500Ω output impedance will form a 106 Hz lowpass filter. Since the thermal time constant of the VTEMP output is much slower than the 9.4 ms time constant formed by the RC, the overall response time of the VTEMP output will not be significantly affected. For much larger capacitors this additional time lag will increase the overall response time of the LM56. 01289320 FIGURE 5. Reducing Errors Caused by Bias Current The circuit shown in Figure 5 will reduce the effective bias current error for VT2 as discussed in Section 3.0 to be equivalent to the error term of VT1. For this circuit the effect of the bias current on the first trip point can be defined by the following equations: where IB = 300 nA (the maximum specified error). Similarly, bias current affect on VT2 can be defined by: www.national.com 10 sensing element is at the same temperature as the heat sink, the sensor’s leads are mounted to pads that have feed throughs to the back side of the PC board. Since the LM56 is sensing the temperature of the actual PC board the back side of the PC board also has large ground plane to help conduct the heat to the device. The comparator’s output goes low if the heat sink temperature rises above a threshold set by R1, R2, and the voltage reference. This fault detection output from the comparator now can be used to turn on a cooling fan. The circuit as shown in design to turn the fan on when heat sink temperature exceeds about 80˚C, and to turn the fan off when the heat sink temperature falls below approximately 75˚C. (Continued) where IB = 300 nA (the maximum specified error). The current shown in Figure 6 is a simple overtemperature detector for power devices. In this example, an audio power amplifier IC is bolted to a heat sink and an LM56 Celsius temperature sensor is mounted on a PC board that is bolted to the heat sink near the power amplifier. To ensure that the 01289321 FIGURE 6. Audio Power Amplifier Overtemperature Detector 01289322 FIGURE 7. Simple Thermostat 11 www.national.com LM56 Application Hints LM56 Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC Order Number LM56BIM, LM56BIMX, LM56CIM or LM56CIMX NS Package Number M08A 8-Lead Molded Mini Small Outline Package (MSOP) (JEDEC REGISTRATION NUMBER M0-187) Order Number LM56BIMM, LM56BIMMX, LM56CIMM, or LM56CIMMX NS Package Number MUA08A www.national.com 12 LM56 Dual Output Low Power Thermostat Notes National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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