LM89

SNIS128D – AUGUST 2002 – REVISED JUNE 2014

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10.2.2 Detailed Design Procedure

10.2.2.1 Compensating For Diode Nonideality

In order to compensate for the errors introduced by nonideality, the temperature sensor is calibrated for a

particular processor. The LM89 is calibrated for the nonideality of a 0.13 micron, Mobile Pentium 4, 1.0021.

When a temperature sensor calibrated for a particular processor type is used with a different processor type or a

given processor type has a nonideality that strays from the typical, errors are introduced.

Temperature errors associated with nonideality may be reduced in a specific temperature range of concern

through use of the offset registers (11h and 12h).

10.2.3 Application Curves

LM89 is connected to diode-connected MMBT3904.

2N3904 and LM89 junction temperatures are equivalent during

test.

Figure 17. Remote Temperature Accuracy

Figure 16. Local Temperature Accuracy

10.3 Do's and Don'ts

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 LM89. 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 LM89's SMBCLK input. Additional resistance can be added

in series with the SMBData 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 SMBData and SMBCLK lines.

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