Detailed Description
The MAX6516–MAX6519 fully integrated temperature
switches incorporate a fixed reference, an analog tem-
perature sensor, and a comparator. The temperature at
which the two reference voltages are equal determines
the temperature trip point. OUT is an analog voltage
that varies with the die’s temperature. Pin-selectable
2°C or 10°C hysteresis keeps the digital output from
oscillating when the die temperature approaches the
threshold temperature. The MAX6516 and MAX6518
have an active-high, push-pull output structure that can
sink or source current. The MAX6517 and MAX6519
have an active-low, open-drain output structure that
can only sink current. The internal power-on reset cir-
cuit guarantees the logic output is at its +25°C state for
at least 50µs.
Analog Output
OUT is an analog output that is proportional to the die
temperature. OUT voltage range is between 0.77V to
2.59V, within the temperature range of -45°C to
+125°C. For applications with a switching threshold of
-45°C, the supply voltage must be greater than 4.5V.
The temperature-to-voltage transfer function is approxi-
mately linear and can be described by the quadratic
equation:
V
OUT
= 1.8015 - 10.62mV (T - 30) + 1.1µV (T - 30)
2
where T = temperature in °C.
In most cases, a linear approximation can be applied:
V
OUT
= 1.8015 - 10.62mV (T - 30)
Therefore,
Hysteresis Input
The HYST input selects the devices’ temperature hys-
teresis and prevents the output from oscillating when the
temperature approaches the trip point. Connect HYST to
V
CC
for 2°C hysteresis or to GND for 10°C hysteresis.
Logic Temperature Indicators
Overtemperature Indicator (Hot Thresholds)
TOVER and TOVER designations apply to thresholds
above T
A
= +25°C (+35°C, +45°C, +55°C, +65°C, +75°C,
+85°C, +95°C, +105°C, +115°C). All “hot” thresholds are
positive temperatures.
The overtemperature indicator output is open-drain
active low (TOVER) or push-pull active high (TOVER).
TOVER goes low when the die temperature exceeds
the factory-programmed temperature threshold. TOVER
should be pulled up to a voltage no greater than 5.5V
with a 100kΩ pullup resistor. TOVER is a push-pull
active-high CMOS output that goes high when the die
temperature exceeds the factory-programmed temper-
ature threshold.
Undertemperature Indicator (Cold Thresholds)
TUNDER and TUNDER designations apply to thresholds
below T
A
= +25°C (+15°C, +5°C, -5°C, -15°C, -25°C,
-35°C, -45°C). The undertemperature indicator output is
open drain, active low (TUNDER), or push-pull active
high (TUNDER). TUNDER goes low when the die tem-
perature goes below the factory-programmed tempera-
ture threshold. TUNDER should be pulled up to a
voltage no greater than 5.5V with a 100kΩ pullup resis-
tor. TUNDER is a push-pull active-high CMOS output
that goes high when the die temperature falls below the
factory-programmed temperature threshold.
Applications Information
Temperature-Window Alarm
The MAX6516/MAX6518 logic outputs assert when the
die temperature is outside the factory-programmed
range. Combining the outputs of two devices creates
an over/undertemperature alarm. Two MAX6516s or
two MAX6518s 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. The
MAX6516 push-pull output stages can be ORed to
produce a thermal out-of-range alarm (Figure 1).
More favorably, two MAX6517s or two MAX6519s can
be directly wire-ORed with a single external resistor to
accomplish the same task. The temperature window
alarms shown in Figure 2 can be used to accurately
determine when a device’s temperature falls out of the
-5°C to +75°C range. The thermal overrange signal can
be used to assert a thermal shutdown, power-up,
recalibration, or other temperature-dependent function.
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