Integrated-sensor fan drivers for simplified designs

October 06, 2014 // By Graham Prophet
Diodes Inc. has added two all-in-one single-phase 12V fan motor drivers for low to medium voltage brushless DC fan control in consumer, home appliance, industrial and office equipment. High levels of integration, miniature package options and thermal handling offered in the AH5772 and AH5773 fan drivers enable a reduction in component count.

By integrating both high-sensitivity Hall sensors and companion input amplifiers, the devices can be used with lower strength fan motor magnets, achieving additional cost savings. Maintaining voltage and thermal coefficients over a wide operating range, the sensors' tolerances are also very small, helping to reduce variability in motor performance and simplifying manufacturing and testing.

A built-in low RDS(on) H-bridge output stage enables these compact fan drivers to support source and sink currents of up to 500 mA continuous, 1A peak, matching the performance of much larger and more complex drivers and pre-drivers. The devices' low profile, low pin-count package options are MSOP8-EP and U-DFN2020-6 (planned Q4 2014) for the AH5773 and TO-94 for the AH5772.

The fan drivers have an operating voltage range from 2.4V to 18V, that suits a variety of brushless DC cooling fan applications, with the low start-up voltage permitting fan operation down to 20% of nominal 12V supply. An operating temperature range of -40ºC to +105ºC makes them suitable for thermally demanding enclosures.

While both drivers provide fan speed regulation via voltage input control, the AH5773 also offers more accurate speed control by varying the duty ratio of a PWM signal train applied to a dedicated PWM input. When the AH5773's PWM pin is pulled low for longer than 65 msec, the device enters standby mode, consuming 100 µA typical. When the PWM pin is pulled high, the drive output is reactivated. This quick start function can be used during locked rotor protection phase to restart fan motor before full lock-off time has elapsed.

To help protect the fan motor coil from over-heating or burning out, both fan drivers incorporate locked rotor protection, which shuts down the driver output in the event of locked rotor detection. Once the rotor lock is released, the drive automatically restarts. Lock-detect, shutdown and auto-restart timing are all handled internally and do not require external timing capacitors.

Further safeguard features integrated