Motors and Control

High-Integration Chipset for Small Electric Motors in Traction Applications

Electric traction for small vehicles is getting more and more popular among two- and three-wheelers ranging from pedal-assist e-bikes to e-scooters and motorbikes. DC brushless (BLDC) motors are generally used for traction due to their efficiency, size and reliability. Typical power for pedal-assist e-bikes ranges from 250W to 500W, while for e-scooters, motorbikes and three-wheelers power can reach up to 5 kW and more.

The other key elements that affect system performance (autonomy, motor power, etc.) are batteries which have typical voltages ranging from 24V up to 72V. 48V batteries are becoming the most common choice especially for e-scooters. Optimized battery voltage as well motor power are instrumental for correct IC selection.

STMicroelectronics offers an AEC-qualified integrated chipset for the ECU (Electronic Control Unit) up to 48V electric BLDC traction motors

The key building blocks of ST’s proposal are an SPC5 32-bit automotive MCU based on the Power Architecture family, an L9907 BLDC pre-driver and 100V MOSFETs for the bridge-inverter implementation.

Particularly suitable for motor control applications, the SPC560P automotive MCU includes specific peripherals such as 6-channel PWM outputs (FlexPWM) which can be used to control each single phase of a 3-phase BLDC motor, two ADCs whose shared signal can acquire the 3-phase current and a Cross Timer Unit (CTU) to completely avoid having to use the CPU for in-time acquisitions of the state variables during the control cycle (PWM cycle, half PWM cycle or number of PWM cycles).

Typical application circuit (click on schematic to enlarge)

The L9907 is able to drive 6 MOSFET transistors for 3-phase BLDC motor applications. The circuit is suitable for operation in environments with a high supply voltage such as double-battery or 48V systems. Supply-related pins are capable of withstanding up to 90V.

Moreover, the L9907 is able to control its six pre-driver channels independently. In this way it is possible to implement all kinds of electric motor control strategies. The device offers programmability for a base gate output current via an external resistor.

It is possible to select among 4 gate output current levels though the SPI bus even while the application is running. All channels are protected against short-circuits and the device is protected against over-temperature conditions.

The integrated boost regulator provides sufficient gate charge for all PowerMOS down to a battery voltage of 6V. All pre-drivers have dedicated connections with the MOSFET sources. The device offers programmability for a base gate output current via an external resistor.

Moreover, via SPI, it is possible to select among 4 gate output current levels even while the application is running. All channels are protected against short circuit and the device is protected against overtemperature conditions.

In addition, the boost converter implements an over voltage protection to allow safe functionality of pre-drivers in all battery voltage conditions. During over voltage conditions, BST_C voltage is limited by temporarily switching off the boost regulator and pre-drivers are allowed to operate. Boost will be self re-enabled as soon as the output voltage decreases to an acceptable value.

The device is equipped with 2 current sense amplifiers. Both have SPI selectable amplifier gain (10, 30, 50 and 100) and output offset voltage level in order to allow max flexibility for phase or ground current sense strategy. All I/O pins are 35V compatible. Full diagnostic is available through SPI. The device is available in TQFP64 and bare die, depending on the application requirements.

The device is protected against Shoot Through events.

Key features of the L9907 include:

  • AEC-Q100 qualified
  • Supply voltage from 6V to 54V for working in single (12V systems), double (24V systems) and 48V battery applications
  • The device can withstand -7V to 90V at the FET high-side Driver pins
  • Low standby current consumption
  • 3 V internal regulator supplied by Vcc pin
  • Boost regulator for full Rdson down to 6V and over voltage protection
  • 3 low-side + 3 high-side drivers
    • PWM operation up to 20kHz
    • Gate driver current adjustable via SPI in 4 steps. Range set via external resistor. Maximum gate controlled current 600mA
    • Source connection to each MOSFET
  • Input pin for each gate driver
  • 2-differential current sense amplifiers:
    • Output offset selectable via SPI (0.2*Vcc offset for ground shunt resistors connection, 0.5*Vcc offset for phase shunt resistors connection)
    • All the amplifier gain factors are programmable (10, 30, 50, 100)
  • 8 MHz, 16-bit SPI
    • Full diagnostic
    • Programmable parameters:
      • Cross conduction dead time with a fixed minimum value
      • 4 current steps driving the PowerMOS gates (25%, 50%, 75%, 100%)
      • Phase or ground selection of current sense amplifier
      • Gain values for the current sense amplifiers
      • Zero current output voltage (offset) for the current sense amplifiers
      • Over voltage threshold selection for single or double battery operation
      • Short circuit detection thresholds for the low-side and the high-side MOSFETs (drain to source voltage monitor).
    • Protection and diagnostic
      • FET driver:
        • FET driver supply Undervoltage (UV) diagnostic;
        • Gate to source output voltage limit;
        • Gate to source passive switch off.
      • Power supply pins VB and VCC:
        • Overvoltage (OV), Undervoltage (UV) diagnostic and protection
      • All logic pins withstand 35V
      • Power MOSFET drain to source voltage drop measurement for overcurrent protection
      • Over-temperature diagnostic and shutdown
      • Fault status flag output

BLDC system block diagram (click on image to enlarge)

A wide selection of 100V N-channel power MOSFETs with different output currents and RDS(on) according to application requirements is also part of ST’s product portfolio.

Each component has its own development toolchain and set of collaterals; a complete motor demonstrator based on this chipset equipped with a FOC control library is also available.

STMicroelectronics NV
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