7.3.1 Conversion Sequence

The LM95214 takes approximately 190 ms to convert the Local Temperature, Remote Temperatures 1 through 4, and to update all of its registers. These conversions for each thermal diode are addressed in a round robin sequence. Only during the conversion process the busy bit (D7) in Status register (02h) is high. The conversion rate may be modified by the Conversion Rate bits found in the Configuration Register (03h). When the conversion rate is modified a delay is inserted between each round of conversions, the actual time for each round remains at 190 ms (typical all channels enabled). The time a round takes depends on the number of channels that are on. Different conversion rates will cause the LM95214 to draw different amounts of average supply current as shown in Figure 10. This curve assumes all the channels are on. If channels are turned off the average current will drop because the round robin time will decrease and the shutdown time will increase during each conversion interval.

Figure 10. Conversion Rate Effect on Power Supply Current

7.3.2 Power-On-Default States

The LM95214 always powers up to these known default states. The LM95214 remains in these states until after the first conversion.

1. All Temperature readings set to 0°C until the end of the first conversion
2. Remote offset for all channels 0°C
3. Configuration: Active converting, Fault Queue enabled for Remote 3 and 4
4. Continuous conversion with all channels enabled, time = 1 s
5. Enhanced digital filter enabled for Remote 1 and 2
6. Status Registers depends on state of thermal diode inputs
7. Local and Remote Temperature Limits for TCRIT1, TCRIT2 and TCRIT3 outputs:

Table 2. Temperature Channel limits

OUTPUT PIN	TEMPERATURE CHANNEL LIMIT
	REMOTE 4 (°C)	REMOTE 3 (°C)	REMOTE 2 (°C)	REMOTE 1 (°C)	LOCAL (°C)
TCRIT1	Masked, 85	Masked, 85	110	110	Masked, 85
TCRIT2	85	85	85	85	85
TCRIT3	85	85	Masked, 85	Masked, 85	Masked, 85

8. Manufacturers ID set to 01h
9. Revision ID set to 79h

7.3.3 SMBus Interface

The LM95214 operates as a slave on the SMBus, so the SMBCLK line is an input and the SMBDAT line is bidirectional. The LM95214 never drives the SMBCLK line and it does not support clock stretching. According to SMBus specifications, the LM95214 has a 7-bit slave address. Three SMBus device address can be selected by connecting A0 (pin 6) to either Low, Mid-Supply, or High voltages. The LM95214 has the following SMBus slave address:

7.3.4 Temperature Conversion Sequence

Each of the 5 temperature channels of LM95214 can be turned OFF independent from each other through the Channel Enable Register. Turning off unused channels will increase the conversion speed in the fastest conversion speed mode. If the slower conversion speed settings are used, disabling unused channels will reduce the average power consumption of LM95214.

7.3.4.1 Digital Filter

To suppress erroneous remote temperature readings due to noise as well as increase the resolution of the temperature, the LM95214 incorporates a digital filter for Remote 1 and 2 Temperature Channels. When a filter is enabled the filtered readings are used for the TCRIT comparisons. There are two possible digital filter settings that are enabled through the Filter Setting Register at register address 0Fh. The filter for each channel can be set according to the following table:

Table 4. Digital Filter Settings

R1F[1:0] OR R2F[1:0]		FILTER SETTING
0	0	No Filter
0	1	Filter (equivalent to Level 2 filter of the LM86/LM89)
1	0	Reserved
1	1	Enhanced Filter (Filter with transient noise clipping)

Figure 11, Figure 12, and Figure 13 describe the filter output in response to a step input and an impulse input.

Figure 11. Seventeen and Fifty Degree Step Response

Figure 13. Impulse Response With Input Transients Greater Than 4°C

Figure 12. Impulse Response With Input Transients Less Than 4°C

Figure 14. Digital Filter Response in a Typical Intel Processor on a 65 nm or 90 nm Process. The Filter Curves Were Purposely Offset for Clarity.

Figure 14 shows the filter in use in a typical system. Note that the two curves have been purposely offset for clarity. Inserting the filter does not induce an offset as shown.

7.3.5 Fault Queue

To suppress erroneous TCRIT1,TCRIT2 and TCRIT3 triggering the LM95214 incorporates a Fault Queue for the unfiltered remote channels 3 and 4. The Fault Queue acts to ensure the remote temperature measurement of these channels is genuinely beyond the corresponding Tcrit limit by not triggering until three consecutive out of limit measurements have been made, see Figure 15 for an example. The Fault Queue defaults on upon power-up. The fault queue for channels 3 and 4 can be turned ON or OFF through bits 0 and 1 of the Configuration Register. When the fault queue is enabled, the TCRIT1, TCRIT2 and TCRIT3 pins will be triggered if the temperature is above the Tcrit limit for 3 consecutive conversions and the corresponding mask bit is 0 in the TCRIT Mask registers. Similarly the temperature needs to be below the Tcrit limit minus the hysteresis value for three consecutive conversions for the TCRIT1, TCRIT2 and TCRIT3 pins to deactivate.

Figure 15. Fault Queue Response Diagram (With 0°C Hysteresis)

7.3.6 Temperature Data Format

Temperature data can only be read from the Local and Remote Temperature value registers. The data format for all temperature values is left justified 16-bit word available in two 8-bit registers. Unused bits will always report 0. All temperature data is clamped and will not roll over when a temperature exceeds full-scale value.

Remote temperature data for all channels can be represented by an 11-bit, two's complement word or unsigned binary word with an LSb (Least Significant Bit) equal to 0.125°C.

When the digital filter is enabled on Remote 1 and 2 channels temperature data is represented by a 13-bit unsigned binary or 12-bit plus sign (two's complement) word with an LSb equal to 0.03125°C.

Local Temperature data is only represented by an 11-bit, two's complement, word with an LSb equal to 0.125°C.

7.3.7 SMBDAT Open-Drain Output

The SMBDAT output is an open-drain output and does not have internal pullups. A high level will not be observed on this pin until pullup current is provided by some external source, typically a pullup resistor. Choice of resistor value depends on many system factors but, in general, the pullup resistor must be as large as possible without effecting the SMBus desired data rate. This will minimize any internal temperature reading errors due to internal heating of the LM95214. The maximum resistance of the pullup to provide a 2.1-V high level, based on LM95214 specification for High Level Output Current with the supply voltage at 3 V, is 82 kΩ (5%) or 88.7 kΩ (1%).

7.3.8 TCRIT1, TCRIT2, and TCRIT3 Outputs

The LM95214's TCRIT pins are active-low open-drain outputs and do not include internal pullup resistors. A high level will not be observed on these pins until pullup current is provided by some external source, typically a pullup resistor. Choice of resistor value depends on many system factors but, in general, the pullup resistor must be as large as possible without effecting the performance of the device receiving the signal. This will minimize any internal temperature reading errors due to internal heating of the LM95214. The maximum resistance of the pullup to provide a 2.1-V high level, based on LM95214 specification for High Level Output Current with the supply voltage at 3 V, is 82 kΩ (5%) or 88.7 kΩ (1%). The three TCRIT pins can each sink 6 mA of current and still ensured a Logic Low output voltage of 0.4 V. If all three pins are set at maximum current this will cause a power dissipation of 7.2 mW. This power dissipation combined with a thermal resistance of 77.8°C/W will cause the LM95214's junction temperature to rise approximately 0.6°C and thus cause the Local temperature reading to shift. This can only be cancelled out if the environment that the LM95214 is enclosed in has stable and controlled air flow over the LM95214, as airflow can cause the thermal resistance to change dramatically.

7.3.9 TCRIT Limits and TCRIT Outputs

Figure 16 describes a simplified diagram of the temperature comparison and status register logic. Figure 17, Figure 18, and Figure 19 describe simplified logic diagrams of the circuitry associated with the status registers, mask registers, and the TCRIT output pins.

Figure 16. Temperature Comparison Logic and Status Register Simplified Diagram

Figure 17. TCRIT1 Mask Register, Status Register 1 and 2, and TCRIT1 Output Logic Diagram

Figure 19. TCRIT3 Mask Register, Status Register 1 and 4, and TCRIT3 Output Logic Diagram

Figure 18. TCRIT2 Mask Register, Status Register 1 and 3, and TCRIT2 Output Logic Diagram

If enabled, local temperature is compared to the user programmable Local Tcrit Limit Register (Default Value = 85°C). The result of this comparison is stored in Status Register 2, Status Register 3 and Status Register 4 (see Figure 16). The comparison result can trigger TCRIT1 pin, TCRIT2 pin or TCRIT3 pin depending on the settings in the TCRIT1 Mask, TCRIT2 Mask and TCRIT3 Mask Registers (see Figure 17, Figure 18, and Figure 19). The comparison result can also be read back from the Status Register 2, Status Register 3 and Status Register 4.

If enabled, remote temperature 1 is compared to the user programmable Remote 1 Tcrit-1 Limit Register (Default Value 110°C) and Remote 1 Tcrit-2 Limit Register (Default Value = 85°C). The result of this comparison is stored in Status Register 2, Status Register 3 and Status Register 4 (see Figure 16). The comparison result can trigger TCRIT1 pin, TCRIT2 pin or TCRIT3 pin depending on the settings in the TCRIT1 Mask, TCRIT2 Mask and TCRIT3 Mask Registers (see Figure 17, Figure 18, and Figure 19). The comparison result can also be read back from the Status Register 2, Status Register 3 and Status Register 4. The remote temperature 2 operates in a similar manner to remote temperature 1 using its associated user programmable limit registers: Remote 2 Tcrit-1 Limit Register (Default Value 110°C) and Remote 2 Tcrit-2 Limit Register (Default Value = 85°C). When enabled, the remote temperature 3 is compared to the user programmable Remote 3 Tcrit Limit Register (Default Value 85°C). The comparison result can trigger TCRIT1 pin, TCRIT2 pin or TCRIT3 pin depending on the settings in the TCRIT1 Mask, TCRIT2 Mask and TCRIT3 Mask Registers. The comparison result can also be read back from the Status Register 2, Status Register 3 and Status Register 4. The remote temperature 4 operates in a similar manner to remote temperature 3 using its associated user programmable limit register: Remote 4 Tcrit Limit Register (Default Value 85°C).

Figure 20. TCRIT Response Diagram (Masking Options Not Included)

The TCRIT response diagram of Figure 20 shows the local temperature interaction with the Tcrit limit and hysteresis value. As can be seen in the diagram when the local temperature exceeds the Tcrit limit register value the LTn Status bit is set and the T_CRITn output(s) is/are activated. The Status bit(s) and outputs are not deactivated until the temperature goes below the value calculated by subtracting the Common Hysteresis value programmed from the limit. This diagram mainly shows an example function of the hysteresis and is not meant to show complete function of the possible settings and options of all the TCRIT outputs and limit values.

7.4.1 Diode Fault Detection

The LM95214 is equipped with operational circuitry designed to detect fault conditions concerning the remote diodes. In the event that the D+ pin is detected as shorted to GND, D−, V_DD or D+ is floating, the Remote Temperature reading is –128.000°C if signed format is selected and 0°C if unsigned format is selected. In addition, the appropriate status register bits RD1M or RD2M (D1 or D0) are set.

7.4.2 Communicating With the LM95214

The data registers in the LM95214 are selected by the Command Register. At power-up the Command Register is set to 00, the location for the Read Local Temperature Register. The Command Register latches the last location it was set to. Each data register in the LM95214 falls into one of three types of user accessibility:

1. Read only
2. Write only
3. Write/Read same address

A Write to the LM95214 will always include the address byte and the command byte. A write to any register requires one data byte.

Reading the LM95214 can take place either of two ways:

1. If the location latched in the Command Register is correct (most of the time it is expected that the Command Register will point to one of the Read Temperature Registers because that will be the data most frequently read from the LM95214), then the read can simply consist of an address byte, followed by retrieving the data byte.
2. If the Command Register needs to be set, then an address byte, command byte, repeat start, and another address byte will accomplish a read.

The data byte has the most significant bit first. At the end of a read, the LM95214 can accept either acknowledge or No Acknowledge from the Master (No Acknowledge is typically used as a signal for the slave that the Master has read its last byte). It takes the LM95214 190 ms (typical, all channels enabled) to measure the temperature of the remote diodes and internal diode. When retrieving all 11 bits from a previous remote diode temperature measurement, the master must insure that all 11 bits are from the same temperature conversion. This may be achieved by reading the MSB register first. The LSB will be locked after the MSB is read. The LSB will be unlocked after being read. If the user reads MSBs consecutively, each time the MSB is read, the LSB associated with that temperature will be locked in and override the previous LSB value locked-in.

Figure 21. Serial Bus Write to the Internal Command Register Followed by a the Data Byte

Figure 22. Serial Bus Write to the Internal Command Register

Figure 23. Serial Bus Read From a Register With the Internal Command Register Preset to Desired Value

Figure 24. Serial Bus Write Followed by a Repeat Start and Immediate Read

7.4.3 Serial Interface Reset

In the event that the SMBus Master is RESET while the LM95214 is transmitting on the SMBDAT line, the LM95214 must be returned to a known state in the communication protocol. This may be done in one of two ways:

1. When SMBDAT is LOW, the LM95214 SMBus state machine resets to the SMBus idle state if either SMBDAT or SMBCLK are held low for more than 35ms (t_TIMEOUT). Note that according to SMBus specification 2.0 all devices are to timeout when either the SMBCLK or SMBDAT lines are held low for 25 to 35 ms. Therefore, to insure a timeout of all devices on the bus the SMBCLK or SMBDAT lines must be held low for at least 35 ms.
2. When SMBDAT is HIGH, have the master initiate an SMBus start. The LM95214 will respond properly to an SMBus start condition at any point during the communication. After the start the LM95214 will expect an SMBus Address byte.

7.4.4 One-Shot Conversion

The One-Shot register is used to initiate a round of conversions and comparisons when the device is in standby mode, after which the device returns to standby. This is not a data register and it is the write operation that causes the one-shot conversion. The data written to this address is irrelevant and is not stored. A zero will always be read from this register. All the channels that are enabled in the Channel Enable Register will be converted once and the TCRIT1, TCRIT2, and TCRIT3 pins will reflect the comparison results based on this round of conversion results of the channels that are not masked.

7.5.1 LM95214 Registers

Command register selects which registers will be read from or written to. Data for this register must be transmitted during the Command Byte of the SMBus write communication.

P0-P7: Command