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TMP03 Fiches technique(PDF) 5 Page - Analog Devices |
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TMP03 Fiches technique(HTML) 5 Page - Analog Devices |
5 / 16 page TMP03/TMP04 REV. 0 –5– Table I. Counter Size and Clock Frequency Effects on Quantization Error Maximum Maximum Maximum Quantization Quantization Count Available Temp Required Frequency Error (+25 C) Error (+77 F) 4096 +125 °C 94 kHz 0.284 °C 0.512 °F 8192 +125 °C 188 kHz 0.142 °C 0.256 °F 16384 +125 °C 376 kHz 0.071 °C 0.128 °F Optimizing Counter Characteristics Counter resolution, clock rate, and the resultant temperature decode error that occurs using a counter scheme may be determined from the following calculations: 1. T1 is nominally 10 ms, and compared to T2 is relatively insensitive to temperature changes. A useful worst-case assumption is that T1 will never exceed 12 ms over the specified temperature range. T1 max = 12 ms Substituting this value for T1 in the formula, temperature ( °C) = 235 – ([T1/T2] × 400), yields a maximum value of T2 of 44 ms at 125 °C. Rearranging the formula allows the maximum value of T2 to be calculated at any maximum operating temperature: T2 (Temp) = (T1max × 400)/(235 – Temp) in seconds 2. We now need to calculate the maximum clock frequency we can apply to the gated counter so it will not overflow during T2 time measurement. The maximum frequency is calculated using: Frequency (max) = Counter Size/ (T2 at maximum temperature) Substituting in the equation using a 12-bit counter gives, Fmax = 4096/44 ms 94 kHz. 3. Now we can calculate the temperature resolution, or quantization error, provided by the counter at the chosen clock frequency and temperature of interest. Again, using a 12-bit counter being clocked at 90 kHz (to allow for ~5% temperature over-range), the temperature resolution at +25 °C is calculated from: Quantization Error ( °C) = 400 × ([Count1/Count2] – [Count1 – 1]/[Count2 + 1]) Quantization Error ( °F) = 720 × ([Count1/Count2] – [Count1 – 1]/[Count2 + 1]) where, Count1 = T1max × Frequency, and Count2 = T2 (Temp) × Frequency. At +25°C this gives a resolution of better than 0.3 °C. Note that the temperature resolution calculated from these equations improves as temperature increases. Higher temperature resolution will be obtained by employing larger counters as shown in Table I. The internal quantization error of the TMP03/TMP04 sets a theoretical minimum resolution of approximately 0.1 °C at +25°C. Self-Heating Effects The temperature measurement accuracy of the TMP03/TMP04 may be degraded in some applications due to self-heating. Errors introduced are from the quiescent dissipation, and power dissipated by the digital output. The magnitude of these temperature errors is dependent on the thermal conductivity of the TMP03/TMP04 package, the mounting technique, and effects of airflow. Static dissipation in the TMP03/TMP04 is typically 4.5 mW operating at 5 V with no load. In the TO-92 package mounted in free air, this accounts for a temperature increase due to self-heating of ∆T = P DISS × ΘJA = 4.5 mW × 162°C/W = 0.73°C (1.3°F) For a free-standing surface-mount TSSOP package, the temperature increase due to self-heating would be ∆T = P DISS × ΘJA = 4.5 mW × 240°C/W = 1.08°C (1.9°F) In addition, power is dissipated by the digital output which is capable of sinking 800 µA continuous (TMP04). Under full load, the output may dissipate P DISS = 0.6 V () 0.8 mA () T2 T1 + T 2 For example with T2 = 20 ms and T1 = 10 ms, the power dissipation due to the digital output is approximately 0.32 mW with a 0.8 mA load. In a free-standing TSSOP package this accounts for a temperature increase due to output self-heating of ∆T = P DISS × ΘJA = 0.32 mW × 240°C/W = 0.08°C (0.14°F) This temperature increase adds directly to that from the quiescent dissipation and affects the accuracy of the TMP03/ TMP04 relative to the true ambient temperature. Alternatively, when the same package has been bonded to a large plate or other thermal mass (effectively a large heatsink) to measure its temperature, the total self-heating error would be reduced to approximately ∆T = P DISS × ΘJC = (4.5 mW + 0.32 mW) × 43°C/W = 0.21°C (0.37°F) Calibration The TMP03 and TMP04 are laser-trimmed for accuracy and linearity during manufacture and, in most cases, no further adjustments are required. However, some improvement in performance can be gained by additional system calibration. To perform a single-point calibration at room temperature, measure the TMP03/TMP04 output, record the actual measurement temperature, and modify the offset constant (normally 235; see the Output Encoding section) as follows: Offset Constant = 235 + (TOBSERVED – TTMP03OUTPUT) A more complicated two-point calibration is also possible. This involves measuring the TMP03/TMP04 output at two temp- eratures, Temp1 and Temp2, and modifying the slope constant (normally 400) as follows: Slope Constant = Temp 2 − Temp1 T1@ Temp1 T 2@ Temp1 − T1@ Temp 2 T 2@ Temp 2 where T1 and T2 are the output high and output low times, respectively. |
Numéro de pièce similaire - TMP03 |
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Description similaire - TMP03 |
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