MAX6501 Maxim, MAX6501 Datasheet - Page 6

• Manufacturer Part Number: MAX6501
• Description: Low-Cost / +2.7V to +5.5V / Micropower Temperature Switches in SOT23 and TO-220
• Manufacturer: Maxim

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:
where P
MAX6501–MAX6504, and θ
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
Low-Cost, +2.7V to +5.5V, Micropower
Temperature Switches in SOT23 and TO-220
Figure 2. Microprocessor Alarm/Reset
6
_______________________________________________________________________________________
+3.3V
DISSIPATION
V
µP
CC
SHUTDOWN
∆T
Applications Information
J
RESET
= P
INT
OR
is the power dissipated by the
DISSIPATION
Thermal Considerations
JA
R
100k
HEAT
PULL-UP
is the package’s thermal
TOVER
x θ
HYST
JA
MAX6501
GND
V
CC
GND
power is dissipated within the IC. This corresponds to a
0.042°C shift in the die temperature in the SOT23-5.
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.
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.
Figure 3. Overtemperature Fan Control
+5V
V
µP
CC
Temperature-Window Alarm
HEAT
GND
V
CC
Temperature Monitor
MAX6502
Low-Cost, Fail-Safe
GND
TOVER
HYST
FAN