New Three Phase Motor Controllers From Solid State Supplies Satisfies Automotive Designs
Two new 3-phase brushless DC (BLDC) motor controllers for use with N-channel external power MOSFETs have been introduced by Solid State Supplies. Incorporating much of the circuitry required to design a cost effective three-phase motor drive system, and specifically designed for automotive applications, the A3930 and A3931 will operate with a reduced gate drive at battery voltages down to 5.5V.
Satisfying the key automotive requirement of operation over a wide input supply range, a unique charge pump regulator provides adequate (>10 V) gate drive for battery voltages down to 7V.
Power dissipation in the charge pump is minimised by switching from a voltage doubling mode at low supply voltage to a dropout mode at the nominal running voltage of 14 V. A bootstrap capacitor is used to provide the above-battery supply voltage required for N-channel MOSFETs. An internal charge pump for the high-side drive allows for DC (100% duty cycle) operation.
Internal fixed-frequency PWM current control circuitry can be used to regulate the maximum load current. The peak load current limit is set by the selection of an input reference voltage and external sensing resistor. The PWM frequency is set by a user-selected external RC timing network.
For added flexibility, the PWM input can be used to provide speed and torque control, which enables the internal current control circuit to set the maximum current limit and efficiency is enhanced by using synchronous rectification. The power FETs are protected from shoot-through by integrated crossover control with dead time. The dead time can be set by a single external resistor.
The lead free A3930 and A3931 have a very small, 81mm2, footprint and only differ in their response to the all-zero combination on the Hall inputs. In this state, the A3930 indicates a logic fault, but the A3931 pre-positions the motor in an unstable starting position suitable for start-up algorithms in microprocessor driven “sensor-less” control systems.
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