Quad Linear Fan-Speed Controller

The MAX6620 controls the speeds of up to four fans using four independent linear voltage outputs. The drive voltages for the fans are controlled directly over the I²C interface. Each output drives the base of an external bipolar transistor or the gate of a FET in high-side drive configuration. Voltage feedback at the fan's power-supply terminal is used to force the correct output voltage.

The MAX6620 offers two methods for fan control. In RPM mode, the MAX6620 monitors four fan tachometer logic outputs for precise (±1%) control of fan RPM and detection of fan failure. In DAC mode, each fan is driven with a voltage resolution of 9 bits and the tachometer outputs of the fans are monitored for failure.

The DACSTART input selects the fan power-supply voltage at startup to ensure appropriate fan drive when power is first applied. A watchdog feature turns the fans fully on to protect the system if there are no valid I²C communications within a preset timeout period.

The MAX6620 operates from a 3.0V to 5.5V power supply with low 250µA supply current, and the I²C-compatible interface makes it ideal for fan control in a wide range of cooling applications. The MAX6620 is available in a 28-pin TQFN package and operates over the -40°C to +125°C automotive temperature range.

Applications

* Communications Equipment * Consumer Products * Servers * Storage Equipment

* Controls Up to Four Independent Fans with Linear (DC) Drive

* Uses Four External Low-Cost Pass Transistors

* 1% Accuracy Precision RPM Control

* Controlled Voltage Rate-Of-Change for Best Acoustics

* I²C Bus Interface

* 3.0V to 5.5V Supply Voltage Range

* 250µA (typ) Operating Supply Current

* 3µA (typ) Shutdown Supply Current

* Small 5mm x 5mm Footprint