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ADM1031ARQZ-R7 Folha de dados(PDF) 11 Page - ON Semiconductor |
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ADM1031ARQZ-R7 Folha de dados(HTML) 11 Page - ON Semiconductor |
11 / 30 page ADM1031 http://onsemi.com 11 4. Try to minimize the number of copper/solder joints, which can cause thermocouple effects. Where copper/solder joints are used, make sure that they are in both the D+ and D– path and at the same temperature. Thermocouple effects should not be a major problem as 1 °C corresponds to about 200 mV, and thermocouple voltages are about 3 mV/°C of temperature difference. Unless there are two thermocouples with a big temperature differential between them, thermocouple voltages should be much less than 200 mV. 5. Place a 0.1 mF bypass capacitor close to the ADM1031. 6. If the distance to the remote sensor is more than 8 inches, the use of twisted pair cable is recommended. This works up to about 6 to 12 feet. 7. For extra long distances (up to 100 feet), use a shielded twisted pair cable, such as the Belden #8451 microphone cable. Connect the twisted pair to D+ and D– and the shield to GND close to the ADM1031. Leave the remote end of the shield unconnected to avoid ground loops. Because the measurement technique uses switched current sources, excessive cable and/or filter capacitance can affect the measurement. When using long cables, the filter capacitor C1 can be reduced or removed. In any case the total shunt capacitance should not exceed 1000 pF. Cable resistance can also introduce errors. One ohm series resistance introduces about 0.5 °C error. Addressing the Device ADD (Pin 13) is a three−state input. It is sampled, on powerup to set the lowest two bits of the serial bus address. Up to three addresses are available to the systems designer via this address pin. This reduces the likelihood of conflicts with other devices attached to the system management bus. The Interrupt System The ADM1031 has two interrupt outputs, INT and THERM. These have different functions. INT responds to violations of software programmed temperature limits and is maskable. THERM is intended as a “fail−safe” interrupt output that cannot be masked. If the temperature is below the low temperature limit, the INT pin is asserted low to indicate an out−of−limitcondition. If the temperature exceeds the high temperature limit, the INT pin is also asserted low. A third limit, THERM limit, can be programmed into the device to set the temperature limit above which the overtemperature THERM pin is asserted low. The behavior of the high limit and THERM limit is as follows: 1. Whenever the temperature measured exceeds the high temperature limit, the INT pin is asserted low. 2. If the temperature exceeds the THERM limit, the THERM output asserts low. This can be used to throttle the CPU clock. If the THERM−to−Fan Enable bit (Bit 7 of THERM behavior/revision register) is cleared to 0, then the fans do not run full−speed. The THERM limit can be programmed at a lower temperature than the high temperature limit. This allows the system to run in silent mode, where the CPU can be throttled while the cooling fan is off. If the temperature continues to increase, and exceeds the high temperature limit, an INT is generated. Software can then decide whether the fan should run to cool the CPU. This allows the system to run in silent mode. 3. If the THERM−to−Fan Enable bit is set to 1, then the fan runs full−speed whenever THERM is asserted low. In this case, both throttling and active cooling take place. If the high temperature limit is programmed to a lower value than the THERM limit, exceeding the high temperature limit asserts INT low. Software could change the speed of the fan depending on temperature readings. If the temperature continues to increase and exceeds the THERM limit, THERM asserts low to throttle the CPU and the fan runs full−speed. This allows the system to run in performance mode, where active cooling takes place and the CPU is only throttled at high temperature. Using the high temperature limit and the THERM limit in this way allows the user to gain maximum performance from the system by only slowing it down, should it be at a critical temperature. Although the ADM1031 does not have a dedicated interrupt mask register, clearing the appropriate enable bits in Configuration Register 2 clears the appropriate interrupts and masks out future interrupts on that channel. Disabling interrupt bits prevents out−of−limit conditions from generating an interrupt or setting a bit in the status registers. Using THERM as an Input The THERM pin is an open−drain input/output pin. When used as an output, it signals overtemperature conditions. When asserted low as an output, the fan is driven full−speed if the THERM−to−Fan Enable bit is set to 1 (Bit 7 of Register 0 ×3F). When THERM is pulled low as an input, the THERM bit (Bit 7) of Status Register 2 is set to 1, and the fans are driven full−speed. Note that the THERM−to−Fan Enable bit has no effect whenever THERM is used as an input. If THERM is pulled low as an input, and the THERM−to−Fan Enable bit = 0, then the fans are still driven full−speed. The THERM−to−Fan Enable bit only affects the behavior of THERM when used as an output. Status Registers All out−of−limit conditions are flagged by status bits in Status Register 1 (0 ×02) and Status Register 2 (0×03). Bit 0 (Alarm Speed) and Bit 1 (Fan Fault) of Status Register 1, once set, can be cleared by reading Status Register 1. Once the alarm speed bit is cleared, this bit is not reasserted on the next monitoring cycle even if the condition still persists. This bit can be reasserted only if the fan is no longer at alarm |
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