TMP01GBC AD [Analog Devices], TMP01GBC Datasheet - Page 9

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

REV. C
APPLICATIONS INFORMATION
Self-Heating Effects
In some applications the user should consider the effects of self-
heating due to the power dissipated by the open-collector out-
puts, which are capable of sinking 20 mA continuously. Under full
load, the TMP01 open-collector output device is dissipating
which in a surface-mount SO package accounts for a tempera-
ture increase due to self-heating of
This will of course directly affect the accuracy of the TMP01
and will for example cause the device to switch the heating out-
put “OFF” 2 degrees early. Alternatively, bonding the same
package to a moderate heatsink limits the self-heating effect to
approximately
which is a much more tolerable error in most systems. The
VREF and VPTAT outputs are also capable of delivering suffi-
cient current to contribute heating effects and should not be
ignored.
Buffering the Voltage Reference
As mentioned before, the reference output VREF is used to gen-
erate the temperature setpoint programming voltages for the
TMP01 and also is used to determine the hysteresis temperature
band by the reference load current I
buffer amplifier is typically capable of 500 A output drive into
as much as 50 pF load (max). Exceeding this load will affect the
accuracy of the reference voltage, could cause thermal sensing
errors due to dissipation, and may induce oscillations. Selection
of a low drift buffer functioning as a voltage follower with high
input impedance will ensure optimal reference accuracy, and
will not affect the programmed hysteresis current. Amplifiers
which offer the low drift, low power consumption, and low cost
appropriate to this application include the OP295, and members
of the OP90, OP97, OP177 families, and others as shown in the
following applications circuits.
Figure 13. Comparator Input Offset Distribution
–0.4
8
7
6
5
4
3
2
1
0
T = P
T = P
–0.32
DISS
DISS
P
DISS
–0.24
= 0.6 V
JA
JC
= .012 W
= .012 W
–0.16
OFFSET – mV
.020A = 12 mW
–0.08
VREF
158 C/W = 1.9 C.
43 C/W = 0.52 C.
. The on-board output
0
T
V+ = +5V
I
VREF
A
0.08
= +25 C
= 5 A
0.16
–9–
With excellent drift and noise characteristics, VREF offers a
good voltage reference for data acquisition and transducer exci-
tation applications as well. Output drift is typically better than
–10 ppm/ C, with 315 nV/ Hz (typ) noise spectral density at
1 kHz.
Preserving Accuracy Over Wide Temperature Range
Operation
The TMP01 is unique in offering both a wide-range temperature
sensor and the associated detection circuitry needed to imple-
ment a complete thermostatic control function in one mono-
lithic device. While the voltage reference, setpoint comparators,
and output buffer amplifiers have been carefully compensated to
maintain accuracy over the specified temperature range, the user
has an additional task in maintaining the accuracy over wide op-
erating temperature ranges in this application. Since the TMP01
is both sensor and control circuit, in many applications it is pos-
sible that the external components used to program and inter-
face the device may be subjected to the same temperature
extremes. Thus it may be necessary to locate components in
close thermal proximity to minimize large temperature differen-
tials, and to account for thermal drift errors where appropriate,
such as resistor matching tempcos, amplifier error drift, and
the like. Circuit design with the TMP01 requires a slightly dif-
ferent perspective regarding the thermal behavior of electronic
components.
Thermal Response Time
The time required for a temperature sensor to settle to a speci-
fied accuracy is a function of the thermal mass of the sensor,
and the thermal conductivity between the sensor and the object
being sensed. Thermal mass is often considered equivalent to
capacitance. Thermal conductivity is commonly specified using
the symbol Q, and can be thought of as the reciprocal of thermal
resistance. It is commonly specified in units of degrees per watt
of power transferred across the thermal joint. Thus, the time re-
quired for the TMP01 to settle to the desired accuracy is depen-
dent on the package selected, the thermal contact established in
that particular application, and the equivalent power of the heat
source. In most applications, the settling time is probably best
determined empirically.
Figure 14. Zero Hysteresis Current Distribution
10
9
8
7
6
5
4
3
2
1
0
6.2
6.4
6.6
REFERENCE CURRENT – A
6.8
7
7.2
7.4
V+ = +5V
T
7.6
A
= +25 C
TMP01
7.8
8