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LM95235 Datasheet(PDF) 9 Page - National Semiconductor (TI) |
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LM95235 Datasheet(HTML) 9 Page - National Semiconductor (TI) |
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9 / 25 page  1.0 Functional Description The LM95235 is a temperature sensor that measures Local and Remote temperature zones. The LM95235 uses a ∆V be temperature sensing method. A differential voltage, repre- senting temperature, is digitized using a Sigma-Delta analog to digital converter. TruTherm Technology allows the LM95235 to accurately sense the temperature of a thermal diode found on die fabricated using a sub-micron process. For more information on TruTherm Technology see Section 3.0 Application Hints. The LM95235 is compatible with the serial SMBus version 2.0 two-wire serial interface. The LM95235 has OS and TCRIT open-drain digital outputs that indicate the state of the local and remote temperature readings when compared to user-programmable limits. If enabled, the local temperature is compared to the user- programmable Local Shared OS and TCRIT Limit Register (Default Value = 85˚C). The comparison result can trigger the T_CRIT pin and/or the OS pin depending on the settings of the Local TCRIT Mask and OS Mask bits found in Con- figuration Register 1. The comparison result can also be read back from Status Register 1. If enabled, the remote temperature is compared to the user-programmable Remote TCRIT Limit Register (Default Value = 110˚C), and the Re- mote OS Limit Register (Default Value = 85˚C) values. The comparison result can trigger the T_CRIT pin and/or the OS pin depending on the settings of Configuration Register 1. The following table describes the default temperature set- tings for each measured temperature that triggers T_CRIT and/or OS pins: Output Pin Remote, ˚C Local, ˚C T_CRIT 110 85 OS 85 85 The following table describes the limit register mapping to the T_CRIT and/or OS pins: Output Pin Remote Local T_CRIT Remote TCRIT Limit Local Shared OS/TCRIT Limit OS Remote OS Limit Local Shared OS/TCRIT Limit The T_CRIT and OS outputs are open-drain, active low. The remote temperature readings support a programmable digital filter. Based on the settings in Configuration Register 2 a digital filter can be turned on to improve the noise performance of the remote temperature as well as to in- crease the resolution of the temperature reading. If the filter is enabled the filtered readings are used for TCRIT and OS comparisons. The LM95235 may be placed in low power consumption (Standby) mode by setting the STOP/RUN bit found in Configuration Register 1. In the Standby mode, the LM95235’s SMBus interface remains active while all circuitry not required is turned off. In the Standby mode the host can trigger one round of conversions by writing to the One-Shot Register. The value written into this register is not kept. Local and Remote temperatures will be converted once and the T_CRIT and OS pins will reflect the comparison results based on this set of conversions results. All the temperature readings are in 16-bit left-justified word format. The 10-bit plus sign local temperature reading is contained in two 8-bit registers: Local Temp MSB and Local Temp LSB Registers. The remote temperature supports both a 13-bit unsigned and a 12-bit plus sign format. These readings are available in their corresponding registers as described in the LM95235 Register table. The lower 2-bits of the remote temperature reading will contain temperature information only if the digital filter is enabled. If the digital filter is disabled, these two bits will read back 0. The signed and unsigned remote temperature readings are available simultaneously in separate registers, therefore al- lowing both negative temperatures and temperatures 128˚C and above to be measured. All Limit Registers support unsigned temperature format with 1˚C LSb resolution. The Local Shared TCRIT and OS Limit Register is 7 bits for limits between 0˚C and 127˚C. The Remote Temperature TCRIT and OS Limit Registers are 8 bits each for limits between 0˚C and 255˚C. 1.1 CONVERSION SEQUENCE In the power-up default state the LM95235 takes a maximum of 1 second to convert the Local Temperature, Remote Tem- perature, and to update all of its registers. Only during the conversion process is the Busy bit (D7) in Status Register 1 (02h) high. These conversions are addressed in a round- robin sequence. The conversion rate may be modified by the Conversion Rate bits found in the Conversion Rate Register (R/W: 04h/0Ah). When the conversion rate is modified a delay is inserted between conversions, the actual maximum conversion time remains at 72 ms. Different conversion rates will cause the LM95235 to draw different amounts of supply current as shown in Figure 1. 1.2 POWER-ON-DEFAULT STATES LM95235 always powers up to these known default states. The LM95235 remains in these states until after the first conversion. 1. Command Register set to 00h 2. Conversion Rate register defaults to 02h (1 second). 3. Local Temperature set to 0˚C until the end of the first conversion 4. Remote Diode Temperature set to 0˚C until the end of the first conversion 5. Remote OS limit default is 55h (85 ˚C). 6. Local Shared and TCRIT limit default is 55h (85 ˚C). 20174906 FIGURE 1. Conversion Rate Effect on Power Supply Current www.national.com 9 |
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