purpose this application note show apply temperature offset factory-ca

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purpose this application note show apply temperature offset factory-ca

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Offset DS1859 Temperature Reading
purpose this application note show apply temperature offset factory-calibrated temperature sensor reading DS1859. Temperature Offset register should only modified customer's application requires DS1859 internal temperature reading have offset.
Temperature Offset Register
Temperature Offset register (Offset Tmp) located Table Main Device memory addresses (see page DS1859 data sheet). each DS1859, Temperature Offset register programmed with value that calibrates temperature read 25°C when exposed 25°C. strongly suggested that value factory-calibrated Temperature Offset recorded copied into location user memory. Once Temperature Offset register modified, temperature readings will longer represent actual temperature which DS1859 exposed.
Digitally Applied Temperature Offset
Temperature Offset digitally applied offset Temperature Gain value that cannot modified user value guaranteed design). changes Temperature Offset will uniformly applied Temperature Gain. adding subtracting from Temperature Offset value, positive negative offset applied temperature reading, located Table addresses 61h. Figure shows block diagram digital Temperature Offset applied. Modifying Temperature Offset registers invalidates factory calibrated temperature reading digital resistor lookup tables. Temperature Offset registers should only modified there need offset factory-calibrated temperature reading.
Figure Digitally Applied Temperature Offset
FACTORY CALIBRATED INTERNAL TEMPERATURE SENSOR (°C)
DIGITAL TEMPERATURE OFFSET (TABLE AFh)
TEMPERATURE OUTPUT (°C) (REGISTERS 61h) Min: 0000h Max: FFFFh
DS1859
Calculating Temperature Offset
first step calculating value Temperature Offset read factory-calibrated value from Temperature Offset register. value address most significant byte Temperature Offset value address least significant byte Temperature Offset. purposes calculations, this factory calibrated offset called TOFFREAD. This value encoded must XOR'd with B680h attain actual temperature offset value. result called TOFFSET.
(Equation
TOFFREAD B680h TOFFSET
Application Note 3252 Once TOFFSET been calculated, value must converted from decimal. This will produce accurate value reference temperature. value used TOFFSET, there will loss temperature accuracy (1°C) when using remaining equations because decimal portion temperature value will truncated. following equation determine factory-calibrated absolute temperature reference, TABSREF(°C).
(Equation
TOFFSET 81920d ABSREF 128d
Once decimal value TABSREF been calculated, desired temperature offset, TDESIREDOFFSET, added subtracted from TABSREF find temperature offset value, TNEWOFFSET.
(Equation
(TABSREF TDESIREDOFFSET )(128d 81920d TNEWOFFSET
After value TNEWOFFSET been calculated, must converted into then encoded. encode temperature offset, take value TNEWOFFSET with B680h.
(Equation
TNEWOFFSET B680h TOFFWRITE
value TOFFWRITE should then written Temperature Offset register. Table 01h, write most significant byte into address write least significant byte into address AFh.
Temperature Offset Example Calculations
Example following example, Temperature Offset register recalculated that DS1859 exposed 25°C will read 35°C. Therefore, 10°C offset desired. Start reading factory-calibrated Temperature Offset register. this example, that register contains 012Eh. Equation this value with B680h decode temperature offset value. result B7AEh. Converting this value into decimal, 47022d.
012Eh B680h B7AEh 47022d
Next, Equation find factory-calibrated absolute temperature reference, TABSREF, this part. this example, result -272.640625°C.
47022d 81920d 272.640625°C 128d
Since 10°C offset added, Equation calculate temperature offset value, TNEWOFFSET. result 48302d.
272.640625°C 10°C)(128d 81920d 48302d
Convert 48302d BCAEh. Equation encode this offset written into Temperature Offset register. result 0A2Eh.
BCAEh B680h 0A2Eh
Table write register write register +10°C offset.
Application Note 3252 Example this example, Temperature Offset register recalculated that DS1859 exposed 25°C will read 15°C. Therefore, -10°C offset desired. apply negative offset, follow same method stated above determine factory calibrated absolute temperature reference (TABSREF -272.640625°C). -10°C offset, Equation subtract 10°C from -272.640625°C. result 45742d, which equal B2AEh.
272.640625°C 10°C)(128d 81920d 45742d B2AEh
Next, encode temperature-offset value using Equation
B2AEh B680h 042Eh
This value entered into Temperature Offset registers (Table 01h, 2Eh) attain -10°C offset.
Conclusion
This application note showed apply positive negative temperature offset factory-calibrated temperature reading DS1859. This application note only intended customers require temperature offset applied DS1859 temperature sensor reading. Care must taken save factory-calibrated value Temperature Offset register each DS1859 that those values restored should customer require original temperature offset. Altering factory calibrated value Temperature Offset will also require digital resistor lookup tables calculated based temperature readings. Questions/comments/suggestions concerning this application note sent MixedSignal.Apps@dalsemi.com.
Maxim Integrated Products/Dallas Semiconductor Contact Information
Dallas Semiconductor 4401 Beltwood Parkway Dallas, 75244 Tel: 972-371-4448 Maxim Integrated Products, Gabriel Drive Sunnyvale, 94086 Tel: 408-737-7600 Product Literature Samples Requests: (800) 998-8800 Sales Customer Service: (972) 371-6824 World Wide Website: www.maxim-ic.com Product Information: Ordering Information: Site: Tech Support: MixedSignal.Apps@dalsemi.com

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