MAX6502UKP075T(2011) 查看數據表（PDF） - Maxim Integrated

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MAX6502UKP075T
(Rev.:2011)

Low-Cost, +2.7V to +5.5V, Micropower Temperature Switches in SOT23

Maxim Integrated 

Low-Cost, +2.7V to +5.5V, Micropower

Temperature Switches in SOT23

+3.3V

VCC

μP INT

SHUTDOWN

OR

RESET

RPULLUP

VCC

100kΩ

MAX6501

TOVER

HYST GND GND

HEAT

+5V

VCC

VCC

HYST

μP

HEAT

MAX6502

FAN

GND GND TOVER

Figure 2. Microprocessor Alarm/Reset

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 package may be small

enough to fit underneath a socketed µP, allowing the

device to monitor the µP’s temperature directly. Use the

monitor’s output to reset the µP, assert an interrupt, or

trigger an external alarm.

Accurate temperature monitoring depends on the ther-

mal 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 temperature monitor ensure that heat transfers

quickly and reliably.

The rise in die temperature due to self-heating is given

by the following formula:

ΔTJ = 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 package. 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 addi-

tional 0.3mW of power is dissipated within the IC. This

corresponds to a 0.042°C shift in the die temperature in

the SOT23.

Figure 3. Overtemperature Fan Control

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, multi-

ple 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 moni-

tored device cause no permanent damage. The first

temperature 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 out-

put asserts when a wide variety of destructive fault con-

ditions occur, including latchups, short circuits, and

cooling-system failures.

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