GMT G768B (sensor)

Added by ALMICO on 18 feb 2005

The G768B contains a precise digital thermometer, 2 fan controllers, and a system-reset circuit. The G768B is backward compatible with G768, except that there is an additional watchdog function. This function prevents fan from being out of control when system fails. The thermometer reports the temperature of 2 remote sensors and its own package. 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. 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. G768B also contains a 2-channel 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 clock. It uses pulse width modulation (PWM) method and an on-chip MOSFET to control the fan speed to +-2% of the programmed speed. The G768B also turns on the fans by hardware watchdog system. The G768B 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 G768B is available in a small, 16-pin SSOP surface-mount package.