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ADT7490 Datasheet(PDF) 10 Page - ON Semiconductor |
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ADT7490 Datasheet(HTML) 10 Page - ON Semiconductor |
10 / 75 page ADT7490 www.onsemi.com 10 Theory of Operation The ADT7490 is a complete thermal monitor and multiple fan controller for any system requiring thermal monitoring and cooling. The device communicates with the system via a serial system management bus. The serial bus controller has a serial data line for reading and writing addresses and data (Pin 1), and an input line for the serial clock (Pin 2). All control and programming functions for the ADT7490 are performed over the serial bus. In addition, Pin 14 can be reconfigured as an SMBALERT output to signal out-of-limit conditions. Feature Comparisons Between the ADT7490 and ADT7476A The ADT7490 is pin and register map compatible with the ADT7476A. The new or additional features are detailed in the following sections. PECI Input CPU thermal information is provided through the PECI input. The ADT7490 has PECI master capabilities and can read the CPU thermal information through the PECI interface. Each CPU address can have up to two PECI domains. The ADT7490 has the ability to record four PECI temperature readings corresponding to the four PECI addresses of 0x30 to 0x33. The hotter of the two domains at any given address is stored in the PECI value registers. A PECI reading is a negative value, in degrees Celsius, which represents the offset from the thermal control circuit (TCC) activation temperature. PECI information is not converted to absolute temperature reading. PECI information is in a 16-bit twos complement value; however, the ADT7490 records the sign bit as well as the bits from 12:6 in the 16-bit PECI payload. See the Platform Environment Control Interface (PECI) Specification from Intel® for more details on the PECI data format. The PECI format is represented in Table 6. Table 6. PECI DATA FORMAT MSB Upper Nibble MSB Lower Nibble S x x x x x x x Sign Bit Integer Value (0°C to 127°C) There are associated high and low limits for each PECI reading that can be programmed. The limit values take the same format as the PECI reading. Therefore, the programmed limits are not absolute temperatures but a relative offset in degrees Celsius from the TCC activation temperature. An out-of-limit event is recorded as follows: High Limit > Comparison Performed Low Limit ≤ Comparison Performed An out-of-limit event is recorded in the associated status register and can be used to assert the SMBALERT pin. Temperature Data REPLACE Mode The REPLACE mode is configured by setting Bit 4 of Register 0x36. In this mode, the data in the existing Remote 1 registers are replaced by PECI0 data and vice versa. This is a legacy mode that allows the thermal data from CPU1 to be stored in the same registers as in the ADT7476A. This reduces the software changes in systems transitioning from CPUs with thermal diodes to CPUs with a PECI interface. See the PECI Temperature Measurement section for more details. Fan Control Using PECI Information The CPU thermal information from PECI can be used in the existing automatic fan control algorithms. This temperature reading remains relative to TCC activation temperature and the associated AFC control parameters are programmed in relative temperatures as opposed to absolute temperatures, and are in the same format as detailed in Table 6. PECIMIN, TRANGE, and TCONTROL are user defined. Figure 17. Overview of Automatic Fan Speed Control Using PECI Thermal Information TRANGE PWMMAX PWMMIN PWM = 0% PWM = 100% (TMIN) PECIMIN (TMAX) TCONTROL TCC PECI = 0 Dynamic TMIN Fan Control Mode The automatic fan speed control incorporates a feature called dynamic TMIN control. This intelligent fan control feature reduces the design effort required to program the automatic fan speed control loop and improves the system acoustics. VTT Input The VTT voltage is monitored on Pin 8. This voltage is also used as the reference voltage for the PECI interface. The VTT voltage must be connected to the ADT7490 in order for the PECI interface to be operational. IMON Monitoring The IMON input on Pin 19 can be used to monitor the IMON output of ON Semiconductor’s VR10/VR11.1 controllers. IMON is a voltage representation of the CPU current. Using |
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