TMP01
Rev. E | Page 8 of 20
THEORY OF OPERATION
The TMP01 is a linear voltage-output temperature sensor, with
a window comparator that can be programmed by the user to
activate one of two open-collector outputs when a predeter-
mined temperature setpoint voltage has been exceeded. A low
drift voltage reference is available for setpoint programming.
The temperature sensor is basically a very accurate, temperature
compensated, band gap-type voltage reference with a buffered
output voltage proportional to absolute temperature (VPTAT),
accurately trimmed to a scale factor of 5 mV/K.
The low drift 2.5 V reference output VREF is easily divided
externally with fixed resistors or potentiometers to accurately
establish the programmed heat/cool setpoints, independent of
temperature. Alternatively, the setpoint voltages can be supplied
by other ground referenced voltage sources such as user-
programmed DACs or controllers. The high and low setpoint
voltages are compared to the temperature sensor voltage, thus
creating a two-temperature thermostat function. In addition,
the total output current of the reference (I
VREF
) determines the
magnitude of the temperature hysteresis band. The open
collector outputs of the comparators can be used to control a
wide variety of devices.
VPTAT
V+
WINDOW
COMPARATOR
TEMPERATURE
OUTPUT
HYSTERESIS
CURRENT
CURRENT
MIRROR
HYSTERESIS
VOLTAGE
ENABLE
TMP01
VREF
SET
HIGH
SET
LOW
GND
UNDER
OVER
8
5
6
7
1
4
3
2
VOLTAGE
REFERENCE
AND
SENSOR
1kΩ
I
HYS
00333-013
Figure 13. Detailed Block Diagram
TEMPERATURE HYSTERESIS
The temperature hysteresis is the number of degrees beyond
the original setpoint temperature that must be sensed by the
TMP01 before the setpoint comparator is reset and the output
disabled. Figure 14 shows the hysteresis profile. The hysteresis
is programmed by the user by setting a specific load on the
reference voltage output VREF. This output current I
VREF
is also
called the hysteresis current, which is mirrored internally and
fed to a buffer with an analog switch.
HYSTERESIS
HIGH
HYSTERESIS
LOW
LO
HI
OUTPUT
VOLTAGE
OVER, UNDER
TEMPERATURE
HYSTERESIS HIGH =
HYSTERESIS LOW
T
SETLOW
T
SETHIGH
00333-014
Figure 14. TMP01 Hysteresis Profile
After a temperature setpoint is exceeded and a comparator
tripped, the buffer output is enabled. The output is a current
of the appropriate polarity that generates a hysteresis offset volt-
age across an internal 1000 resistor at the comparator input.
The comparator output remains on until the voltage at the
comparator input, now equal to the temperature sensor voltage
VPTAT summed with the hysteresis offset, returns to the
programmed setpoint voltage. The comparator then returns
low, deactivating the open-collector output and disabling the
hysteresis current buffer output. The scale factor for the
programmed hysteresis current is:
I
HYS
= I
VREF
= 5 µA/°C + 7 µA
Thus, since VREF = 2.5 V, with a reference load resistance
of 357 k or greater (output current 7 A or less), the temper-
ature setpoint hysteresis is zero degrees. Larger values of load
resistance only decrease the output current below 7 A and
have no effect on the operation of the device. The amount of
hysteresis is determined by selecting a value of load resistance
for VREF.
PROGRAMMING THE TMP01
In the basic fixed setpoint application utilizing a simple resistor
ladder voltage divider, the desired temperature setpoints are
programmed in the following sequence:
1. Select the desired hysteresis temperature.
2. Calculate the hysteresis current I
VREF
.
3. Select the desired setpoint temperatures.
4. Calculate the individual resistor divider ladder values
needed to develop the desired comparator setpoint voltages
at SET HIGH and SET LOW.
