TMP01EP Просмотр технического описания (PDF) - Analog Devices
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TMP01EP Datasheet PDF : 16 Pages
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TMP01
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 will be reset and the output dis-
abled. Figure 2 shows the hysteresis profile. The hysteresis is
programmed by the user by setting a specific load on the refer-
ence voltage output VREF. This output current IVREF is also
called the hysteresis current, which is mirrored internally and
fed to a buffer with an analog switch.
HYSTERESIS
LOW
HI
HYSTERESIS
HIGH
OUTPUT
VOLTAGE
OVER, UNDER
HYSTERESIS HIGH =
HYSTERESIS LOW
The hysteresis current is readily calculated, as shown. For
example, for 2 degrees of hysteresis, IVREF = 17 µA. Next, the
setpoint voltages VSETHIGH and VSETLOW are determined using
the VPTAT scale factor of 5 mV/K = 5 mV/(°C + 273.15),
which is 1.49 V for +25°C. We then calculate the divider resis-
tors, based on those setpoints. The equations used to calculate
the resistors are:
VSETHIGH = (TSETHIGH + 273.15)(5 mV/°C)
VSETLOW = (TSETLOW + 273.15) (5 mV/°C)
R1 (kΩ) = (VVREF – VSETHIGH)/IVREF =
= (2.5 V – VSETHIGH)/IVREF
R2 (kΩ) = (VSETHIGH – VSETLOW)/IVREF
R3 (kΩ) = VSETLOW/IVREF
LO
TSETLOW
TEMPERATURE
TSETHIGH
Figure 2. TMP01 Hysteresis Profile
After a temperature setpoint has been exceeded and a compara-
tor tripped, the buffer output is enabled. The output is a cur-
rent of the appropriate polarity which generates a hysteresis
offset voltage across an internal 1000 Ω resistor at the compara-
tor input. The comparator output remains “on” until the volt-
age at the comparator input, now equal to the temperature
sensor voltage VPTAT summed with the hysteresis offset, has
returned 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:
IHYS = IVREF = 5 µA/°C + 7 µA
Thus since VREF = 2.5 V, with a reference load resistance of
357 kΩ or greater (output current 7 µA or less), the temperature
setpoint hysteresis will be zero degrees. See the temperature
programming discussion below. Larger values of load resistance
will only decrease the output current below 7 µA and will have
no effect on the operation of the device. The amount of hyster-
esis is determined by selecting a value of load resistance for
VREF, as shown below.
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 IVREF.
3. Select the desired setpoint temperatures.
4. Calculate the individual resistor divider ladder values needed
to develop the desired comparator setpoint voltages at
SETHIGH and SETLOW.
VVREF = 2.5V
(VVREF – VSETHIGH )/IVREF = R1
VSETHIGH
(VSETHIGH – VSETLOW )/IVREF = R2
VSETLOW
VSETLOW /IVREF = R3
GND
1
IVREF
2
3
4
8 V+
TMP01 7 OVER
6 UNDER
5 VPTAT
Figure 3. TMP01 Setpoint Programming
The total R1 + R2 + R3 is equal to the load resistance needed
to draw the desired hysteresis current from the reference, or
IVREF.
The formulas shown above are also helpful in understanding the
calculation of temperature setpoint voltages in circuits other
than the standard two-temperature thermostat. If a setpoint
function is not needed, the appropriate comparator should be
disabled. SETHIGH can be disabled by tying it to V+, SET-
LOW by tying it to GND. Either output can be left unconnected.
218
K
248
273
298
323
348
373
398
–55
°C
–25 –18 0
25
50
75
100
125
–67
°F
–25 0
32 50 77 100
150
200 212 257
1.09
VPTAT
1.24 1.365 1.49 1.615 1.74 1.865 1.99
Figure 4. Temperature—VPTAT Scale
–6–
REV. C
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