G768D

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 ±5 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^TM) 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 1, in two's-complement format. Measurements can be done automatically and autonomously, with the conversion rate programmed by the user or programmed to operate in a single-shot mode. The adjustable rate allows the user to control the supply-current drain.

G768D also contains a fan speed controller. It connects directly to the fans and performs closed-loop control of the fan speed independently. The only external component required is a 10µF capacitor per channel. It determines the current fan speed based on the fan rotation pulses and an externally supplied 32.768KHz clock.