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LM82CIMQAX Datasheet(PDF) 10 Page - National Semiconductor (TI) |
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LM82CIMQAX Datasheet(HTML) 10 Page - National Semiconductor (TI) |
10 / 17 page 1.0 Functional Description (Continued) 1.4 POWER ON RESET DEFAULT STATES LM82 always powers up to these known default states: 1. Command Register set to 00h 2. Local Temperature set to 0˚C 3. Remote Temperature set to 0˚C until the LM82 senses a diode present between the D+ and D− input pins. 4. Status Register set to 00h. 5. Configuration Register set to 00h; INT enabled and all T_CRIT setpoints enabled to activate T_CRIT_A. 6. Local and Remote T_CRIT set to 127˚C 1.5 SMBus INTERFACE The LM82 operates as a slave on the SMBus, so the SMBCLK line is an input (no clock is generated by the LM82) and the SMBData line is bi-directional. According to SMBus specifications, the LM82 has a 7-bit slave address. Bit 4 (A3) of the slave address is hard wired inside the LM82 to a 1. The remainder of the address bits are controlled by the state of the address select pins ADD1 and ADD0, and are set by connecting these pins to ground for a low, (0) , to V CC for a high, (1), or left floating (TRI-LEVEL). Therefore, the complete slave address is: A6 A5 A4 1 A2 A1 A0 MSB LSB and is selected as follows: Address Select Pin State LM82 SMBus Slave Address ADD0 ADD1 A6:A0 binary 0 0 001 1000 0 TRI-LEVEL 001 1001 0 1 001 1010 TRI-LEVEL 0 010 1001 TRI-LEVEL TRI-LEVEL 010 1010 TRI-LEVEL 1 010 1011 1 0 100 1100 1 TRI-LEVEL 100 1101 1 1 100 1110 The LM82 latches the state of the address select pins during the first read or write on the SMBus. Changing the state of the address select pins after the first read or write to any device on the SMBus will not change the slave address of the LM82. 1.6 TEMPERATURE DATA FORMAT Temperature data can be read from the Local and Remote Temperature, T_CRIT, and HIGH setpoint registers; and writ- ten to the T_CRIT and HIGH setpoint registers. Temperature data is represented by an 8-bit, two’s complement byte with an LSB (Least Significant Bit) equal to 1˚C: Temperature Digital Output Binary Hex +125˚C 0111 1101 7Dh +25˚C 0001 1001 19h +1˚C 0000 0001 01h 0˚C 0000 0000 00h −1˚C 1111 1111 FFh −25˚C 1110 0111 E7h −55˚C 1100 1001 C9h 1.7 OPEN-DRAIN OUTPUTS The SMBData, INT and T_CRIT_A outputs are open-drain outputs and do not have internal pull-ups. A “high” level will not be observed on these pins until pull-up current is pro- vided from some external source, typically a pull-up resistor. Choice of resistor value depends on many system factors but, in general, the pull-up resistor should be as large as possible. This will minimize any internal temperature reading errors due to internal heating of the LM82. The maximum resistance of the pull up, based on LM82 specification for High Level Output Current, to provide a 2.1V high level, is 30k Ω. Care should be taken in a noisy system because a high impedance pull-up will be more likely to couple noise into the signal line. 1.8 DIODE FAULT DETECTION Before each external conversion the LM82 goes through an external diode fault detection sequence. If D+ input is shorted to V CC or floating then the temperature reading will be +127 ˚C, and the OPEN bit in the Status Register will be set. If the T_CRIT setpoint is set to less than +127 ˚C then the D+ input RTCRIT bit in the Status Register will be set which will activate the T_CRIT_A output, if enabled. If a D+ is shorted to GND or D−, its temperature reading will be 0 ˚C and its OPEN bit in the Status Register will not be set. www.national.com 10 |
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