ST Gate Drivers to Boost Economy, Efficiency for 3-Phase Brushless Motors - News

STMicroelectronics recently introduced a pair of triple half-bridge gate drivers, the STDRIVE102H and STDRIVE102BH, for three-phase brushless DC motors. Designed for devices like cordless power tools, e-bikes, and automation systems, these drivers integrate current programmability and a suite of protection features.

The STDRIVE102H and STDRIVE102BH each feature three half-bridge gate drivers that can source up to 1 A and sink up to 2 A, driving six external N-channel MOSFETs with precise gate current control. By programming the IGATE and TCC analog inputs, designers can finely adjust the gate drive strength and the duration of constant-current phases and modify the power stage behavior to specific system needs.

An integrated charge pump ensures the high-side MOSFETs can remain fully on throughout a 100% PWM duty cycle. The pump operates from a dedicated VM supply input that is distinct from the device's VS supply input, permitting flexible voltage domain configurations. The charge pump output (VBOOT) powers the high-side drivers, while two integrated LDOs, one at 12 V and another at 3.3 V, support the low-side drivers and the embedded analog front end.

The two devices differentiate themselves through their support for single-shunt (STDRIVE102H) or three-shunt (STDRIVE102BH) current sensing. The STDRIVE102BH includes three high-bandwidth operational amplifiers and three comparators, while the STDRIVE102H integrates a single amplifier and two comparators for real-time phase current monitoring and overcurrent protection. Each channel’s VDS is monitored independently, and fault conditions trigger an nFAULT open-drain signal with minimal propagation delay. The BH variant also adds a FLAG pin to indicate degraded VCC conditions.

Additional design safeguards include UVLO on all supplies (VCC, VDD, and charge pump), thermal shutdown at 150°C, and programmable VDS fault thresholds. Devices are housed in compact QFN packages measuring 6 mm x 6 mm for the STDRIVE102BH and 5 mm x 5 mm for the STDRIVE102H.

Brushless DC (BLDC) motors rely on electronic commutation, where precise switching of phase currents is necessary to maintain torque and rotational speed. In typical implementations, external gate drivers are used to control the power MOSFETs that drive each phase. These drivers must provide sufficient gate charge at controlled speeds to enable efficient switching, avoid shoot-through, and reduce electromagnetic interference.

A main challenge in such systems is balancing switching speed with electromagnetic compatibility (EMC) and thermal efficiency. Faster switching reduces conduction losses but increases the risk of ringing and EMI. Slower transitions, while gentler on the system, may cause higher switching losses. To address this, designers often resort to fixed external gate resistors. However, these resistors introduce fixed behaviors that are suboptimal across varying loads and operating conditions.

To this end, the STDRIVE102x series introduces programmable gate current control, which adjusts gate charge profiles in real time using simple analog inputs. This eliminates the need for external gate resistors and provides a tunable method for controlling slew rate dynamically.

STMicroelectronics claims its STDRIVE102H and STDRIVE102BH are well-suited for power-constrained environments that may benefit from intelligent fault handling and efficient standby operation. ST is offering evaluation boards for both ICs, along with software support through the X-CUBE-MCSDK STM32 motor-control software development kit (MCSDK).