Rainbow Electronics MAX6515 - Manual (Page 5)

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:
∆T J = P DISSIPATION x θ JA
where P DISSIPATION is the power dissipated by the
MAX6514/MAX6515, and θ JA is the thermal resistance
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.
MAX6514/MAX6515
Low-Cost, 2.7V to 5.5V Temperature Switches
in a SOT23
_______________________________________________________________________________________ 5
MAX6515UKP075 MAX6515UKN005
V
CC V CC
+5V
100kΩ
GND GND HYST
TUNDER TOVER
GND
OUT OF RANGE
GND HYST
V CC
+5V
SYSTEM
SHUTDOWN
MAX6514UKP075
GND
µP
GND HYST
TOVER
V CC 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