Applications Information

Temperature-Window Alarm

The MAX6515 logic output asserts when the die tem-

perature is outside the factory-programmed range.

Combining the outputs of two devices creates an

over/undertemperature alarm. Two MAX6515s are used

to form two complementary pairs, 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 temperature (Figure 1).

The thermal overrange signal can be used to assert a

thermal shutdown, power-up, recalibration, or other

temperature-dependent function.

Low-Cost, Fail-Safe Temperature

In high-performance/high-reliability applications, multi-

ple temperature monitoring is important. The high-level

integration and low cost of the MAX6514/MAX6515

facilitate the use of multiple temperature monitors to

increase system reliability. The Figure 2 application

uses two MAX6514s with different hot-temperature

thresholds to ensure that fault conditions that can over-

heat the monitored device cause no permanent dam-

age. The first temperature monitor activates the fan

when the die temperature exceeds +45°C. The second

MAX6514 triggers a system shutdown if the die temper-

ature reaches +75°C, preventing damage from a wide

variety of destructive fault conditions, including

latchups, short circuits, and cooling-system failures.

Thermal Considerations

The MAX6514/MAX6515 supply current is typically

22µA. When used to drive high-impedance loads, the

devices dissipate negligible power and self-heating

effects are minimized.

Accurate temperature monitoring depends on the ther-

mal resistance between the device being monitored

and the MAX6514/MAX6515 die. Heat flows in and out

of plastic packages, primarily through the leads. Pin 2

of the 5-pin SOT23 package provides the lowest ther-

mal resistance to the die. Short, wide copper traces

between the MAX6514/MAX6515 and the objects

whose temperature is being monitored ensure heat

transfers occur quickly and reliably. The rise in die tem-

perature due to self-heating is given by the following

formula:

of the package.

The typical thermal resistance is +140°C/W for the 5-

pin SOT23 package. To limit the effects of self-heating,

minimize the output current. For example, if the

MAX6514/MAX6515 sink 1mA, the open-drain 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 tem-

perature in the 5-pin SOT23 package.

Low-Cost, 2.7V to 5.5V Temperature Switches

in a SOT23

_______________________________________________________________________________________

5

MAX6515UKP075

MAX6515UKN005

+5V

100kΩ

GND

GND

HYST

TUNDER

TOVER

GND

OUT OF RANGE

GND

HYST

+5V

SYSTEM

SHUTDOWN

MAX6514UKP075

GND

µP

GND

HYST

TOVER

FAN

CONTROL

MAX6514UKP045

GND

GND

TOVER

HYST

GND

HEAT

HEAT

Figure 1. Temperature-Window Alarms Using the MAX6515

Figure 2. Low-Power, High-Reliability, Fail-Safe Temperature

Monitor