TMP01GBC AD [Analog Devices], TMP01GBC Datasheet - Page 6

• Manufacturer Part Number: TMP01GBC
• Description: Low Power, Programmable Temperature Controller
• Manufacturer: AD [Analog Devices]

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 I
called the hysteresis current, which is mirrored internally and
fed to a buffer with an analog switch.
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
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:
Thus since VREF = 2.5 V, with a reference load resistance of
357 k or greater (output current 7 A 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 A 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 I
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.
OVER, UNDER
VOLTAGE
OUTPUT
LO
Figure 2. TMP01 Hysteresis Profile
HI
I
HYS
HYSTERESIS
T
SETLOW
= I
LOW
VREF
= 5 A/ C + 7 A
HYSTERESIS HIGH =
HYSTERESIS LOW
TEMPERATURE
VREF
resistor at the compara-
.
HYSTERESIS
VREF
HIGH
T
SETHIGH
is also
–6–
The hysteresis current is readily calculated, as shown. For
example, for 2 degrees of hysteresis, I
setpoint voltages V
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:
V
V
R1 (k ) = (V
R2 (k ) = (V
R3 (k ) = V
The total R1 + R2 + R3 is equal to the load resistance needed
to draw the desired hysteresis current from the reference, or
I
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.
VREF
VPTAT
SETHIGH
SETLOW
(V
.
SETHIGH
K
C
(V
F
VREF
–55
1.09
218
–67
= (T
=
= (T
Figure 3. TMP01 Setpoint Programming
(2.5 V – V
Figure 4. Temperature—VPTAT Scale
– V
– V
SETLOW
V
VREF
SETLOW
SETHIGH
SETHIGH
SETLOW
SETHIGH
SETLOW
–25
–25 –18
1.24
248
– V
V
SETHIGH
/I
VREF
)/I
)/I
0
/I
+ 273.15) (5 mV/ C)
VREF
VREF
VREF
VREF
V
V
SETHIGH
– V
+ 273.15)(5 mV/ C)
SETHIGH
SETHIGH
SETLOW
= 2.5V
1.365
273
GND
32 50
= R2
= R3
SETLOW
= R1
0
and V
)/I
)/I
1.49
298
VREF
77 100
)/I
25
VREF
I
VREF
SETLOW
VREF
4
1
2
3
=
VREF
1.615
323
50
are determined using
TMP01
= 17 A. Next, the
150
1.74
348
75
200 212
8
7
6
5
1.865
373
100
V+
OVER
VPTAT
UNDER
REV. C
398
1.99
125
257