Brushless full-bridge motor driver provides PWM or DC-voltage speed control

Featuring a bridge-tied-load (BTL) drive architecture to minimize audible switching noise and electromagnetic interference (EMI), the new AM9468 and AM9469 brushless DC motor drivers from Diodes Incorporated provide smart driving of cooling fans in notebook and desktop computers, instrumentation and similar equipment, as well as supporting a wide range of other medium-voltage, low-power, motor-driving applications. Flexible motor speed control is achieved using either an external PWM signal or DC voltage, or a voltage derived from a thermistor network. The AM9468/AM9469 then adjust the duty cycle of the full-bridge output driver stage based on this input signal, while a separate frequency generator provides a tachometer output that allows for external monitoring of motor speed. The BTL architecture amplifies the sinusoidal magnetizing flux density signal used to drive the motor’s coils. This avoids large changes in current during commutation and helps achieve low noise operation. The speed control PWM duty cycle is superimposed on the BTL drive signal. The AM9468/AM9469 feature a built-in quick-start circuit along with rotor lock detection. This protects the motor coil from overheating or burning out, but also ensures an automatic restart when the lock is removed. Other features include a current limit circuit and a Hall bias output, all contributing to a solution that significantly reduces the external component count and PCB footprint, and lowers component and manufacturing costs. The AM9468 is available in a standard, power-capable TSSOP-16 package, while the AM9469 is offered in a thermally enhanced, exposed-paddle TSSOP-16EP package, which can source or sink output currents up to 700mA. Over-temperature protection is provided with a thermal shutdown circuit, a particularly valuable feature for protecting the enclosed coil and PCB of cooling fans found in thermally-demanding consumer applications. Both devices are specified for an operating temperature range from -40C to 105C.