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. With excellent voltage and thermal coefficients over a very 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 500mA 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 UDFN2020-6 (planned Q4 2014) for the AH5773 and TO-94 for the AH5772.

The fan drivers’ wide operating voltage range (2.4V to 18V) 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 2range of -40ºC to +105ºC makes them suitable for even the most 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 65ms, the device enters standby mode, consuming only 100μA (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 into the drivers include over-voltage

protection, which shuts the devices down upon detecting an over-voltage

situation; this puts the AH5772 and AH5773 in standby mode to prevent motor coil stress. An over-temperature shutdown function provides thermal protection for the devices as well.