Resistor-Programmable

SOT Temperature Switches

6

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Applications Information

Thermal Considerations

The MAX6509/MAX6510 supply current is typically

32µA. 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 MAX6509/

MAX6510 package and the device being monitored. In

some applications, the SOT23-5 and SOT23-6 pack-

ages 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 tem-

perature monitoring depends on the thermal resistance

between the device being monitored and the

MAX6509/MAX6510 die.

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

by the following formula:

MAX6509/MAX6510, and

resistance. The typical thermal resistance is 115°C/W

for the SOT23-6 package. To limit the effects of self-

heating, minimize the output currents. For example, if

the MAX6510 sinks 5mA, the output voltage is guaran-

teed to be less than 0.3V; therefore, an additional

1.5mW of power is dissipated within the IC. This corre-

sponds to a 0.173°C shift in the die temperature in the

SOT23-6.

Temperature-Window Detector

The MAX6509/MAX6510 temperature switch outputs

assert when the die temperature is outside the pro-

grammed range. Combining the outputs of a set-cold

and a set-hot device creates an over/undertemperature

detector. The MAX6509/MAX6510 are designed to form

two complementary pairs, each containing one cold trip

point output and one hot trip point output. The assertion

of either output alerts the system to an out-of-range tem-

perature. The MAX6510 push-pull output stages can be

ORed to produce a thermal out-of-range alarm. More

favorably, a MAX6509HAUK-T and MAX6509CAUK-T

can be directly wire-ORed with a single external resis-

tor to accomplish the same task (Figure 5).

The temperature window (alarms or detectors as in

Figure 5) can be used to accurately determine when a

device’s temperature falls out of a programmed range,

for example -3°C to +75°C as shown in Figure 5. The

thermal overrange signal can be used to assert a ther-

MAX6510

+5V

OUT

GND

OUTSET

SET

HYST

µP

FAN

HEAT

THYST = 2°C

SET HOT

OUT

OUT

TEMPERATURE

MAX6509H

MAX6510C

OUTSET = GND

SET COLD

98°C

100°C

100°C

98°C

-38°C

-40°C

-38°C

-40°C

Figure 3. Overtemperature Fan Control

Figure 4. Temperature Response

MAX6509

+3.3V

GND

SET

HYST

µP

HEAT

100k

OUT

INT

SHUTDOWN

OR

RESET

Figure 2. Microprocessor Alarm/Reset