Moteur de recherche de fiches techniques de composants électroniques 

ADM1023 Fiches technique(PDF) 8 Page  ON Semiconductor 

ADM1023 Fiches technique(HTML) 8 Page  ON Semiconductor 
8 / 16 page ADM1023 http://onsemi.com 8 This is given by: (eq. 2) DVBE + nKT q 1n (N) where: K is Boltzmann’s constant. q is the charge on the electron (1.6 10–19 Coulombs). T is the absolute temperature in Kelvins. N is the ratio of the two collector currents. n is the ideality factor of the thermal diode (TD). To measure DVBE, the sensor is switched between operating currents of I and NI. The resulting waveform is passed through a lowpass filter to remove noise, then to a chopperstabilized amplifier that performs the functions of amplification and rectification of the waveform to produce a dc voltage proportional to DVBE. This voltage is measured by the ADC, which gives a temperature output in binary format. To further reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles. Signal conditioning and measurement of the internal temperature sensor are performed in a similar manner. Figure 13 shows the input signal conditioning used to measure the output of an external temperature sensor. This figure shows the external sensor as a substrate PNP transistor, provided for temperature monitoring on some microprocessors, but it could equally well be a discrete transistor. If a discrete transistor is used, the collector is not grounded and should be connected to the base. To prevent ground noise from interfering with the measurement, the more negative terminal of the sensor is not referenced to ground but is biased above ground by an internal diode at the D− input. If the sensor is operating in a noisy environment, C1 may optionally be added as a noise filter. Its value is 1000 pF maximum. See the Layout Considerations section for more information on C1. Sources of Errors on Thermal Transistors Measurement Method; The Effect of Ideality Factor (n) The effects of ideality factor (n) and beta ( b) of the temperature measured by a thermal transistor are described in this section. For a thermal transistor implemented on a submicron process, such as the substrate PNP used on a Pentium III processor, the temperature errors due to the combined effect of the ideality factor and beta are shown to be less than 3C. Equation 2 is optimized for a substrate PNP transistor (used as a thermal diode) usually found on CPUs designed on submicron CMOS processes such as the Pentium III processor. There is a thermal diode on board each of these processors. The n in Equation 2 represents the ideality factor of this thermal diode. This ideality factor is a measure of the deviation of the thermal diode from ideal behavior. According to Pentium III processor manufacturing specifications, measured values of n at 100C are: (eq. 3) nMIN + 1.0057 t nTYPICAL + 1.008 t nMAX + + 1.0125 The ADM1023 takes this ideality factor into consideration when calculating temperature TTD of the thermal diode. The ADM1023 is optimized for nTYPICAL = 1.008; any deviation on n from this typical value causes a temperature error that is calculated below for the nMIN and nMAX of a Pentium III processor at TTD = 100C. (eq. 4) DTMIN + 1.0057 * 1.008 1.008 273.15 Kelvin ) 100° C + +* 0.85° C DTMAX + 1.0125 * 1.008 1.008 273.15 Kelvin ) 100° C + +) 1.67° C Thus, the temperature error due to variation on n of the thermal diode for a Pentium III processor is about 2.5C. In general, this additional temperature error of the thermal diode measurement due to deviations on n from its typical value is given by: (eq. 5) DT + n * 1.008 1.008 273.15 Kelvin ) TTD where TTD is in C. Beta of Thermal Transistor (b) In Figure 13, the thermal diode is a substrate PNP transistor where the emitter current is forced into the device. The derivation of Equation 2 assumed that the collector currents were scaled by N as the emitter currents were also scaled by N. Thus, this assumes that beta ( b) of the transistor is constant for various collector currents. Figure 14 shows typical b variation vs. collector current for Pentium III processors at 100C. The maximum b is 4.5 and varies less than 1% over the collector current range from 7 mA to 300 mA. Figure 14. Variation of b with Collector Currents nb 7 300 b IC (mA) bMAX < 4.5 IC = IE b b+1 IE Expressing the collector current in terms of the emitter current. (eq. 6) IC + IE b (b ) 1)] where: (eq. 7) b 300 mA + b 7 mA (1 ) e) e + Db b and b + b(7mA) Rewriting the equation for DVBE, to include the ideality factor, n, and beta, b yields: (eq. 8) DVBE + nKT q 1n (1 ) e) b ) 1 (1 ) e) b ) 1 N All b variations of less than 1% (e < 0.01) contribute to temperature errors of less than 0.4C. 
