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MAX6502CMN045-T Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX6502CMN045-T Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 8 page Low-Cost, +2.7V to +5.5V, Micropower Temperature Switches in SOT23 and TO-220 6 _______________________________________________________________________________________ Applications Information Thermal Considerations The MAX6501–MAX6504 supply current is typically 30µA. When used to drive high-impedance loads, the devices dissipate negligible power. Therefore, the die temperature is essentially the same as the package temperature. The key to accurate temperature monitor- ing is good thermal contact between the MAX6501– MAX6504 package and the device being monitored. In some applications, the SOT23-5 package may be small enough to fit underneath a socketed µP, allowing the device to monitor the µP’s temperature directly. The TO-220 package can monitor the temperature of a heat sink directly, and presents the lower thermal resistance of the two packages. Use the monitor’s output to reset the µP, assert an interrupt, or trigger an external alarm. Accurate temperature monitoring depends on the thermal resistance between the device being monitored and the MAX6501–MAX6504 die. Heat flows in and out of plastic packages, primarily through the leads. Pin 2 of the SOT23-5 package provides the lowest thermal resistance to the die. Short, wide copper traces leading to the tem- perature monitor ensure that heat transfers quickly and reliably. The rise in die temperature due to self-heating is given by the following formula: ∆TJ = PDISSIPATION x θJA where PDISSIPATION is the power dissipated by the MAX6501–MAX6504, and θJA is the package’s thermal resistance. The typical thermal resistance is 140°C/W for the SOT23-5 package and 75°C/W for the TO-220 pack- age. To limit the effects of self-heating, minimize the output currents. For example, if the MAX6501 or MAX6503 sink 1mA, the output voltage is guaranteed to be less than 0.3V. Therefore, an additional 0.3mW of power is dissipated within the IC. This corresponds to a 0.042°C shift in the die temperature in the SOT23-5. Temperature-Window Alarm The MAX6501–MAX6504 temperature switch outputs assert when the die temperature is outside the factory- programmed range. Combining the outputs of two devices creates an over/undertemperature alarm. The MAX6501/MAX6503 and the MAX6502/MAX6504 are designed to form two complementary pairs, each con- taining one cold trip-point output and one hot trip-point output. The assertion of either output alerts the system to an out-of-range temperature. The MAX6502/MAX6504 push/pull output stages can be ORed to produce a ther- mal out-of-range alarm. More favorably, a MAX6501/ MAX6503 can be directly wire-ORed with a single exter- nal resistor to accomplish the same task (Figure 4). The temperature window alarms shown in Figure 4 can be used to accurately determine when a device’s tem- perature falls out of the -5°C to +75°C range. The ther- mal-overrange signal can be used to assert a thermal shutdown, power-up, recalibration, or other temperature- dependent function. Low-Cost, Fail-Safe Temperature Monitor In high-performance/high-reliability applications, multiple temperature monitoring is important. The high-level integration and low cost of the MAX6501–MAX6504 facilitate the use of multiple temperature monitors to in- crease system reliability. Figure 5’s application uses two MAX6502s with different temperature thresholds to ensure that fault conditions that can overheat the monitored device cause no permanent damage. The first tempera- ture monitor activates the fan when the die temperature exceeds +45°C. The second MAX6502 triggers a system shutdown if the die temperature reaches +75°C. The second temperature monitor’s output asserts when a wide variety of destructive fault conditions occur, includ- ing latchups, short circuits, and cooling-system failures. MAX6502 +5V TOVER GND GND VCC HYST µP FAN HEAT VCC Figure 3. Overtemperature Fan Control MAX6501 +3.3V GND HYST GND VCC µP HEAT VCC RPULL-UP 100k TOVER INT SHUTDOWN OR RESET Figure 2. Microprocessor Alarm/Reset |
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