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TMP01FP Scheda tecnica(PDF) 9 Page - Analog Devices |
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TMP01FP Scheda tecnica(HTML) 9 Page - Analog Devices |
9 / 16 page TMP01 REV. C –9– 8 0 2 1 4 3 5 6 7 –0.4 –0.24 –0.32 0 –0.08 –0.16 0.16 0.08 OFFSET – mV V+ = +5V T A = +25 °C I VREF = 5 µA Figure 13. Comparator Input Offset Distribution 7.2 6.2 7 6.8 6.6 6.4 8 7.8 7.6 7.4 REFERENCE CURRENT – µA 10 0 2 1 4 3 5 6 7 8 9 V+ = +5V T A = +25 °C Figure 14. Zero Hysteresis Current Distribution 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 PDISS = 0.6 V × .020A = 12 mW which in a surface-mount SO package accounts for a tempera- ture increase due to self-heating of ∆T = P DISS × θJA = .012 W × 158°C/W = 1.9°C. 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 ∆T = P DISS × θ JC = .012 W × 43 °C/W = 0.52°C. 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 IVREF. The on-board output buffer amplifier is typically capable of 500 µA 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. 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. |
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