Precision Fan-Speed Controller with Nonvolatile Lookup Table

The MAX31760 integrates temperature sensing along with precision PWM fan control. It accurately measures its local die temperature and the remote temperature of a discrete diode-connected transistor, such as a 2N3906, or a thermal diode commonly found on CPUs, graphics processor units (GPUs), and other ASICs. Multiple temperature thresholds, such as local high/overtemperature (OT) and remote high/overtemperature, can be set by an I2C-compatible interface.

Fan speed is controlled based on the temperature reading as an index to a 48-byte lookup table (LUT) containing user-programmed PWM values. The flexible LUT-based architecture enables the user to program a smooth nonlinear fan speed vs. temperature transfer function to minimize acoustic fan noise. Two tachometer inputs allow measuring the speeds of two fans independently. The active-low FF/FS pin multiplexes an open-drain fan-failure output with a full-speed fan-drive input. When the local or remote OT threshold is exceeded, the active-low SHDN pin is asserted low and can be used to shut down the system. A dedicated active-low ALERT pin reports that either a local or remote high-temperature threshold has been exceeded. Active-low ALERT can be programmed to work in either fault indicator mode or interrupt mode. These features make the device a compact and complete solution for a single-fan or two-fan cooling system.

Applications

* NAS/DAS * Networking Equipment * Servers * STB/DVR

* Operating Settings Stored in Nonvolatile Memory for Automatic Operation at Power-On

* 48-Step Nonvolatile LUT Maps Temperature to PWM Duty Cycle

* Smooth PWM Duty-Cycle Transitions Minimize Audibility of Fan Noise

* Two Tachometer Inputs for Measuring the RPM of Two Fans Independently

* Active-Low FF/FS Pin Multiplexes Fan-Failure Output with Full-Speed Fan-Drive Input

* Accurately Senses Remote and Local Temperature

* Programmable Thermal Diode Ideality Factor Minimizes Ideality Factor Mismatch

* Automatic Series Resistance Cancellation

* Dedicated Active-Low ALERT Pin for Temperature Faults

* Active-Low SHDN Pin Available for System Overtemperature Shutdown

* 3.0V to 3.6V Operating Voltage Range

* -40°C to +125°C Operating Temperature Range