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LM27 Folha de dados(PDF) 6 Page - Texas Instruments |
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LM27 Folha de dados(HTML) 6 Page - Texas Instruments |
6 / 17 page 1.8386 - VTEMP 3.552 x 10 -6 T = -1475.49 + 2.2668 x 10 6 + LM27__L V+ VTEMP GND HYST OS HYST REF TEMP SENSOR + - V+ LM27__N V+ VTEMP GND HYST US HYST REF TEMP SENSOR - + V+ LM27__J V+ VTEMP GND HYST OS HYST REF TEMP SENSOR + - LM27__K V+ VTEMP GND HYST US HYST REF TEMP SENSOR + - LM27 SNIS124D – AUGUST 2002 – REVISED JULY 2013 www.ti.com FUNCTIONAL DESCRIPTION LM27 OPTIONS — Output Pin Options Block Diagrams Figure 1. LM27-_ _J Figure 2. LM27-_ _K Figure 3. LM27-_ _L Figure 4. LM27-_ _N The LM27 can be factory programmed to have a trip point anywhere in-between 120°C to 150°C. Applications Hints AFTER-ASSEMBLY PCB TESTING The LM27's VTEMP output allows after-assembly PCB testing by following a simple test procedure. Simply measuring the VTEMP output voltage will verify that the LM27 has been assembled properly and that its temperature sensing circuitry is functional. The VTEMP output has very weak drive capability that can be overdriven by 1.5mA. Therefore, one can simply force the VTEMP voltage to cause the digital output to change state, thereby verifying that the comparator and output circuitry function after assembly. Here is a sample test procedure that can be used to test the LM27CIM5X-2HJ which has a 140°C trip point. 1. Turn on V+ and measure VTEMP. Then calculate the temperature reading of the LM27 using the equation: VO = (−3.552×10 −6×(T−30)2) + (−10.69576×10−3×(T−30)) + 1.8386V (2) or (3) 2. Verify that the temperature measured in step one is within (±3°C + error of reference temperature sensor) of the ambient/board temperature. The ambient/board temperature (reference temperature) should be measured using an extremely accurate calibrated temperature sensor, which is in close proximity to and mounted on the same PCB as the LM27 perhaps even touching the GND lead of the LM27 if possible. The LM27 will sence the board temperature not the ambient temperature (see MOUNTING CONSIDERATIONS) 3. (a) Observe that OS is high. (b) Drive VTEMP to ground. (c) Observe that OS is now low. (d) Release the VTEMP pin. (e) Observe that OS is now high. 4. (a) Observe that OS is high. (b) Drive VTEMP voltage down gradually. (c) When OS goes low, note the VTEMP voltage. (d) VTEMPTrig = VTEMP at OS trigger (HIGH->LOW) (e) Calculate Ttrig using Equation 3. 6 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LM27 |
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