High Resolution, Small Form Factor Phase Current Sense
for 48V Robotics and Servo Drives

Abstract

This application note introduces the newly released AMC0106M05 and AMC0106M25 functionally isolated modulators. The M05 variant supports a ±50mV, the M25 variant a ±250mV linear input range. Both devices come in a small, lead-less package. The AMC0106Mxx devices enable the design of an accurate and reliable, shunt-based current-sensing subsystem for three-phase inverters with a small form-factor. Typical applications are servo drives, and collaborative or humanoid robots powered from sub-60V power supplies. A circuit design and layout example for a 48V 3-phase GaN inverter with boot bootstrap supply with a ±50A linear current range is presented. The design is based on the AMC0106M05 variant and 1mΩ shunt. Test results are presented showing that a measurement resolution up to 14 effective number of bits (ENOB) is achieved. Phase current measurement is not affected by PWM switching, validating the high immunity against common-mode transients. And finally, this has shown that ripple voltage caused by the bootstrap supply has no effect on the phase current measurement for a wide range of PWM duty cycles.

Trademarks

Sitara™ and C2000™ are trademarks of Texas Instruments.

All trademarks are the property of their respective owners.

1 Introduction

High performance, three-phase inverters operated at 24V to 60V are gaining more traction in emerging industrial applications such as high-efficiency servo drives, and collaborative, surgery, and humanoid robots. Accurate and reliable phase current sensing is crucial in these applications to achieve smooth torque and precise position control. These applications are highly space constrained and the 3-phase inverters are often integrated into the motor. Therefore, a small design size with low profile and the ability to operate at high ambient temperatures up to 125°C are important. In-phase, shunt-based current sensing as shown in Figure 1-1 provides the highest resolution measurement of the motor current and is an industry standard design for high-performance motor drives. TI's newly released AMC0106Mxx functionally isolated modulators in a small, lead-less package enable such measurement in a much smaller design size than what has been achievable so far.

Figure 1-1 48V, 3-Phase Inverter With Shunt-Based, In-Phase Current Sensing