Fan drivers reduce component count & PCB area

6th October 2014

Siobhan O'Gorman

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Suitable for equipment in which space in limited, a pair of single-phase fan motor drivers have been introduced by Diodes Incorporated. The AH5772 and AH5773 all-in-one, 12V drivers offer a high level of integration, miniature package options and thermal handling, enabling a reduction in component count and PCB area.

The drivers are designed for low to medium voltage BLDC fan control in consumer, home appliance, industrial and office equipment. High-sensitivity Hall sensors and companion input amplifiers are integrated within the drivers, allowing them to be used with lower strength fan motor magnets, which reduce cost. To reduce variability in motor performance and simplify manufacturing and testing, the drivers feature high voltage and thermal coefficients which allow the sensors' tolerances to be small.

Through a built-in low RDS(on) H-bridge output stage, the drivers perform as well as larger drivers and pre-drivers. The RDS(on) H-bridge output stage supports source and sink currents of up to 500mA continuous, 1A peak. The AH5773 is offered in MSOP8-EP and U-DFN2020-6 (planned Q4 2014) package options and the AH5772 in TO-94.

Operating from 2.4 to 18V, the drivers are suitable for a variety of BLDC cooling fan applications. Fan operation down to 20% of nominal 12V supply is allowed by the the low start-up voltage. The fan drivers are also suitable for thermally demanding applications, with an operating temperature range from -40 to +105ºC.

Both drivers provide fan speed regulation via voltage input control. By varying the duty ratio of a PWM signal train applied to a PWM input, the AH5773 also offers more accurate speed control. The AH5773 enters standby mode, consuming only 100µA typical, when it's PWM pin is pulled low for longer than 65ms. The drive output is reactivated when the PWM pin is pulled high. During locked rotor protection phase, this function can be used to restart the fan motor before full lock-off time has elapsed.

Locked rotor protection prevents the fan motor coil from over-heating or burning out. In the event of locked rotor detection, this shuts down the driver output. The drive automatically restarts when the rotor lock is released. External timing capacitors are not needed as lock-detect, shutdown and auto-restart timing are handled internally. The drivers are also offered with over-voltage protection and over-temperature shutdown.

Both drivers are sold in 10,000 unit quantities with the AH5773 priced at $0.24 and the AH5772 at $0.21.