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ADT7466ARQZ-REEL Datasheet(PDF) 11 Page - Analog Devices |
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ADT7466ARQZ-REEL Datasheet(HTML) 11 Page - Analog Devices |
11 / 48 page ADT7466 Rev. 0 | Page 11 of 48 FUNCTIONAL DESCRIPTION The ADT7466 is a complete thermal monitor and dual fan controller for any system requiring monitoring and cooling. The device communicates with the system via a serial system management bus (SMBus). The serial data line (SDA, Pin 15) is used for reading and writing addresses and data. The input line, (SCL, Pin 16) is the serial clock. All control and programming functions of the ADT7466 are performed over the serial bus. In addition, an ALERT output is provided to indicate out-of-limit conditions. MEASUREMENT INPUTS The device has three measurement inputs, two for voltage and one for temperature. It can also measure its own supply voltage and can measure ambient temperature with its on-chip temperature sensor. Pin 11 and Pin 12 are analog inputs with an input range of 0 V to 2.25 V. They can easily be scaled for other input ranges by using external attenuators. These pins can also be configured for temperature monitoring by using thermistors or a second remote diode temperature measurement. The ADT7466 can simultaneously monitor the local temperature, the remote temperature by using a discrete transistor, and two thermistor temperatures. Remote temperature sensing is provided by the D+ and D− inputs, to which diode connected, remote temperature sensing transistors such as a 2N3904 or CPU thermal diode can be connected. Temperature sensing using thermistors is carried out by placing the thermistor in series with a resistor. The excitation voltage is provided by the REFOUT pin. The device also accepts input from an on-chip band gap temperature sensor that monitors system ambient temperature. Power is supplied to the chip via Pin 6. The system also monitors VCC through this pin. It is normally connected to a 3.3 V supply. It can, however, be connected to a 5 V supply and monitored without going over range. SEQUENTIAL MEASUREMENT When the ADT7466 monitoring sequence is started, it sequentially cycles through the measurement of analog inputs and the temperature sensors. Measured values from these inputs are stored in value registers, which can be read out over the serial bus, or can be compared with programmed limits stored in the limit registers. The results of out of limit comparisons are stored in the status registers, which can be read over the serial bus to flag out-of-limit conditions. FAN SPEED MEASUREMENT AND CONTROL The ADT7466 has two tachometer inputs for measuring the speed of 3-wire fans, and it has two 8-bit DACs to control the speed of two fans. The temperature measurement and fan speed control can be linked in an automatic control loop, which can operate without CPU intervention to maintain system operating temperature within acceptable limits. The enhanced acoustics feature ensures that fans operate at the minimum possible speed consistent with temperature control, and change speed gradually. This reduces the user’s perception of changing fan speed. INTERNAL REGISTERS OF THE ADT7466 Table 4 provides brief descriptions of the ADT7466’s principal internal registers. More detailed information on the function of each register is given in Table 30 to Table 72. Table 4. Internal Register Summary Register Description Configuration These registers provide control and configuration of the ADT7466 including alternate pinout functionality. Address Pointer This register contains the address that selects one of the other internal registers. When writing to the ADT7466, the first byte of data is always a register address, which is written to the address pointer register. Status These registers provide status of each limit comparison and are used to signal out-of-limit conditions on the temperature, voltage, or fan speed channels. Whenever a status bit is set, the ALERT output (Pin 14) goes low. Interrupt Mask These registers allow interrupt sources to be masked so that they do not affect the ALERT output. Value and Limit The results of analog voltage inputs, temperature, and fan speed measurements are stored in these registers, along with their limit values. Offset These registers allow each temperature channel reading to be offset by a twos complement value written to these registers. PROCHOT Status This register allows the ADT7466 to monitor and time any PROCHOT events gauging system performance. TMIN These registers program the starting temperature for each fan under automatic fan speed control. TRANGE These registers program the temperature-to-fan speed control slope in automatic fan speed control mode for each fan drive output. Enhance Acoustics This register sets the step size for fan drive changes in AFC mode to minimize acoustic noise. |
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