The G7921 contains 3 precise digital thermometers, one fan controllers, hardware and software thermal shutdown, and a system-reset circuit. The thermometers report the temperature of 3 remote sensors. The remote sensors are diode-connected transistors typically a low-cost, easily mounted 2N3904 NPN type or the diode built-in in CPU. Remote accuracy is ±1°C for multiple transistor manufacturer. The G7921 also support offset adjust function via SMBus to fix the error due to different CPU diode or parasitic resistors. The 2-wire serial interface accepts standard System Management Bus (SMBusTM) Write Byte, Read Byte, Send Byte, and Receive Byte commands. The SMBus address is 7ah for write and 7bh for read, and supports writting protection function by command 20h to prevent error behavior of µP. G7921 contains one fan controllers. FAN1 controller performs closed-loop and open-loop control. G7921 determines the current fan speed based on the FG inputs and an externally supplied 32.768KHz clock. The driving ability of FAN1 is 500mA. G7921 also provide ALERT for fan fail and out of control event. The G7921 provides hardware and software thermal shutdown. The hardware thermal shutdown is for the sensor 2. The trigger point is set by external resistors. The trigger points of software thermal shutdown are set via SMBus. If thermal shutdown event occurs, THERM pin outputs low. The G7921 contains a microprocessor (µP) supervisory circuit used to monitor the power supplies in µP and digital systems. Reset threshold is set to 4.38V typical.
