 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LM95231BIMM-1 Datasheet(PDF) 19 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LM95231BIMM-1 Datasheet(HTML) 19 Page - National Semiconductor (TI) |
|
|
19 / 20 page  3.0 Applications Hints (Continued) supporting the MMBT3904 transistor and the Pentium 4 processor on 90nm process without the requirement for additional trims. For most accurate measurements TruTherm mode should be turned on when measuring the Pentium 4 processor on the 90nm process to minimize the error intro- duced by the false non-ideality spread (see Section 3.1.1 Diode Non-Ideality Factor Effect on Accuracy). When a tem- perature sensor calibrated for a particular processor type is used with a different processor type, additional errors are introduced. Temperature errors associated with non-ideality of different processor types may be reduced in a specific temperature range of concern through use of software calibration. Typical Non-ideality specification differences cause a gain variation of the transfer function, therefore the center of the tempera- ture range of interest should be the target temperature for calibration purposes. The following equation can be used to calculate the temperature correction factor (T CF) required to compensate for a target non-ideality differing from that sup- ported by the LM95231. T CF =[( η S− η Processor)÷ η S]x(TCR+ 273 K) (7) where • η S = LM95231 non-ideality for accuracy specification • η T = target thermal diode typical non-ideality • T CR = center of the temperature range of interest in ˚C The correction factor of Equation (7) should be directly added to the temperature reading produced by the LM95231. For example when using the LM95231, with the 3904 mode selected, to measure a AMD Athlon processor, with a typical non-ideality of 1.008, for a temperature range of 60 ˚C to 100 ˚C the correction factor would calculate to: T CF=[(1.003−1.008)÷1.003]x(80+273) =−1.75˚C Therefore, 1.75˚C should be subtracted from the tempera- ture readings of the LM95231 to compensate for the differing typical non-ideality target. 3.2 PCB LAYOUT FOR MINIMIZING NOISE In a noisy environment, such as a processor mother board, layout considerations are very critical. Noise induced on traces running between the remote temperature diode sen- sor and the LM95231 can cause temperature conversion errors. Keep in mind that the signal level the LM95231 is trying to measure is in microvolts. The following guidelines should be followed: 1. V DD should be bypassed with a 0.1µF capacitor in par- allel with 100pF. The 100pF capacitor should be placed as close as possible to the power supply pin. A bulk capacitance of approximately 10µF needs to be in the near vicinity of the LM95231. 2. A 100pF diode bypass capacitor is recommended to filter high frequency noise but may not be necessary. Make sure the traces to the 100pF capacitor are matched. Place the filter capacitors close to the LM95231 pins. 3. Ideally, the LM95231 should be placed within 10cm of the Processor diode pins with the traces being as straight, short and identical as possible. Trace resis- tance of 1 Ω can cause as much as 0.62˚C of error. This error can be compensated by using simple software offset compensation. 4. Diode traces should be surrounded by a GND guard ring to either side, above and below if possible. This GND guard should not be between the D+ and D− lines. In the event that noise does couple to the diode lines it would be ideal if it is coupled common mode. That is equally to the D+ and D− lines. 5. Avoid routing diode traces in close proximity to power supply switching or filtering inductors. 6. Avoid running diode traces close to or parallel to high speed digital and bus lines. Diode traces should be kept at least 2cm apart from the high speed digital traces. 7. If it is necessary to cross high speed digital traces, the diode traces and the high speed digital traces should cross at a 90 degree angle. 8. The ideal place to connect the LM95231’s GND pin is as close as possible to the Processors GND associated with the sense diode. 9. Leakage current between D+ and GND and between D+ and D− should be kept to a minimum. Thirteen nano- amperes of leakage can cause as much as 0.2˚C of error in the diode temperature reading. Keeping the printed circuit board as clean as possible will minimize leakage current. Noise coupling into the digital lines greater than 400mVp-p (typical hysteresis) and undershoot less than 500mV below GND, may prevent successful SMBus communication with the LM95231. SMBus no acknowledge is the most common symptom, causing unnecessary traffic on the bus. Although the SMBus maximum frequency of communication is rather low (100kHz max), care still needs to be taken to ensure proper termination within a system with multiple parts on the bus and long printed circuit board traces. An RC lowpass filter with a 3db corner frequency of about 40MHz is included on the LM95231’s SMBCLK input. Additional resistance can be added in series with the SMBDAT and SMBCLK lines to further help filter noise and ringing. Minimize noise coupling by keeping digital traces out of switching power supply areas as well as ensuring that digital lines containing high speed data communications cross at right angles to the SMBDAT and SMBCLK lines. 20120217 FIGURE 4. Ideal Diode Trace Layout www.national.com 19 |
Similar Part No. - LM95231BIMM-1 |
|
Similar Description - LM95231BIMM-1 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
