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TMP12 Folha de dados(PDF) 7 Page - Analog Devices |
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TMP12 Folha de dados(HTML) 7 Page - Analog Devices |
7 / 14 page TMP12 REV. 0 –7– TEMPERATURE – °C 36 20 -75 -25 25 75 125 175 28 24 32 40 VOL = 1V, V = 5V 22 38 34 30 26 Figure 13. Open-Collector Output Sink Current vs. Temperature TEMPERATURE – °C 700 0 -75 175 -25 25 75 125 600 500 400 300 200 100 a. LOAD = 10mA c. LOAD = 1mA b. LOAD = 5mA a b c V = 5V Figure 14. Open-Collector Voltage vs. Temperature APPLICATIONS INFORMATION A typical application for the TMP12 is shown in Figure 15. The TMP12 package is placed in the same cooling airflow as a high-power dissipation IC. The TMP12’s internal resistor pro- duces a temperature rise which is proportional to air flow, as shown in Figure 16. Any interruption in the airflow will produce an additional temperature rise. When the TMP12 chip tempera- ture exceeds a user-defined setpoint limit, the system controller can take corrective action, such as: reducing clock frequency, shutting down unneeded peripherals, turning on additional fan cooling, or shutting down the system. POWER I.C. PGA PACKAGE PGA SOCKET PC BOARD AIR FLOW TMP12 Figure 15. Typical Application 35 40 45 50 55 60 65 50 100 150 200 250 0 TMP12 P D (mW) a. TMP12 DIE TEMP NO AIR FLOW c. LOW SET POINT b. HIGH SET POINT d. TMP12 DIE TEMP MAX AIR FLOW e. SYSTEM AMBIENT TEMPERATURE a b c d e Figure 16. Choosing Temperature Setpoints Temperature Hysteresis The temperature hysteresis at each setpoint is the number of degrees beyond the original setpoint temperature that must be sensed by the TMP12 before the setpoint compar- ator will be reset and the output disabled. Hysteresis prevents “chatter” and “motorboating” in feedback control systems. For monitoring temperature in computer systems, hysteresis prevents multiple interrupts to the CPU which can reduce system performance. Figure 17 shows the TMP12’s hysteresis profile. The hyster- esis is programmed, by the user, by setting a specific load current on the reference voltage output VREF. This output current, IREF, is also called the hysteresis current. IREF is mir- rored internally by the TMP12, as shown in the functional block diagram, and fed to a buffer with an analog switch. LO HI OUTPUT VOLTAGE OVER, UNDER TEMPERATURE HYSTERESIS LOW HYSTERESIS HIGH = HYSTERESIS LOW TSETLOW TSETHIGH HYSTERESIS HIGH Figure 17. TMP12 Hysteresis Profile After a temperature setpoint has been exceeded and a com- parator tripped, the hysteresis buffer output is enabled. The result is a current of the appropriate polarity which gener- ates a hysteresis offset voltage across an internal 1 k Ω resistor at the comparator input. The comparator output remains “on” until the voltage at the comparator input, now equal to the temperature sensor voltage VPTAT summed with the hysteresis effect, has returned to the pro- grammed setpoint voltage. The comparator then returns |
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