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SpeedFan 4.52
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GMT G768D (sensor)
Added by ALMICO on 18 feb 2005
The G768D contains a precise digital thermometer, a fan controller, and a system-reset circuit. Except for one less fan controller, G768D is backward compatible with G768B. G768D has 2 more functions, fan-failure detection and programmable thermal shutdown signal. The thermometer reports the temperature of 2 remote sensors. The remote sensors are diode-connected transistors typically a low-cost, easily mounted 2N3904 NPN type that replace conventional thermistors or thermocouples. Remote accuracy is +-5C for multiple transistor manufacturers, with no calibration needed. The remote channel can also measure the die temperature of other ICs, such as microprocessors, that contain an on-chip, diode-connected transistor. The 2-wire serial interface accepts standard System Management Bus (SMBus) Write Byte, Read Byte, Send Byte, and Receive Byte commands to program the alarm thresholds and to read temperature data. The data format is 7 bits plus sign, with each bit corresponding to 1C, in two's-complement format. G768D also contains a fan speed controller. It connects directly to the fans and performs closed-loop control of the fan speed independently. It determines the current fan speed based on the fan rotation pulses and an externally supplied 32.768KHz clock. It uses LDO method and an on-chip MOSFET to control the fan speed to +-2% of the programmed speed. The desired fan speed is also programmed viaSMBus. The actual fan speed and fan status can be read via the SMBus. Short-circuit protection is implemented to prevent damages to the fan and this IC itself. The G768D also turns on the fans by hardware watchdog system. The G768D also contains a microprocessor supervisory circuit used to monitor the power supplies in digital systems. They provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with 5V-powered circuits. The G768D is available in a small, 16-pin SSOP surface-mount package.

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