MC33035 drive output circuit

The three upper drive outputs (pins 1, 2, and 24) of the MC33035 are NPN transistors with open collectors. They have a current absorption capacity of 50mA and a withstand voltage of 40V. They can be used to drive the NPN power transistor and P-channel MOSFET power tube of the upper arm of the external inverter bridge. The three lower drive outputs (pins 19, 20, and 21) are push-pull outputs with a current capacity of 100mA, which can directly drive the PNP power transistor and N-channel power MOSFET of the external inverter bridge. The power supply VC of the lower drive output is introduced separately from pin 18, which is separated from the power supply Vcc supplied to the motor. In order to comply with the standard MOSFET gate-drain voltage limit of no more than 20V, an 18V voltage regulator diode should be connected to pin 18 for clamping.

The figure shows a three-phase full-wave commutation waveform diagram, which gives the input position sensor signal, 6 drive outputs, and the corresponding timing diagram of the motor phase current. The first cycle in the figure represents the situation without PWM, while the second cycle represents the situation with 50% PWM.

The inverter bridge of the position sensor BLDCM drive circuit here uses the MPM3003 three-phase inverter bridge power module produced by MOTOROLA, which is a 12-pin power package type three-phase bridge. The three transistors on the upper side are p-channel power MOSFET tubes with an on-resistance of 0.28Ω, and the three transistors on the lower side are N-channel power MOSFET tubes with an on-resistance of 0.15Ω. The drain-source rated voltage of the six tubes is 60V and the current is 10A. Each power tube has a reverse freewheeling diode, and the power supply voltage drop is 10~30V.

This new type of MOS power tube is more stable than the first generation MOS power tube. First, the new MOS power tube has a drain-source diode inside, so it can withstand greater current or voltage changes, while the first generation MOS power tube is often damaged by overload of the reverse recovery diode; second, it is not easy to be damaged by a short-term drain-source overvoltage; and the minimum rated breakdown voltage between the gate and source of the MOS tube inside the MPM3003 is 40V, while the industrial standard is 20V. The high breakdown voltage can not only improve the tube's tolerance to electrostatic discharge and unexpected gate-source voltage pulses, but also extend the working life of the gate oxide layer for all operating voltages.

MPM3003 also has the advantages of small size and isolated package. Compared with installing 6 discrete TO-220 MOS tubes, MPM3003 is easy to install and the required pin area is about half of that. The lead frame of MPM3003 is nickel-plated copper, which can reduce thermal resistance and act as a heat sink. The aluminum lining is coated with epoxy resin film as an insulating layer. To facilitate the attachment of the frame to the aluminum lining, the copper foil on the epoxy resin film is etched to form small islands around the chip, and the aluminum lining is melted into the copper foil before molding. This structure can reduce thermal resistance, prevent the brittleness of ceramic isolation materials, and reduce their consumption.