SLOSE98A December 2022 – September 2023 DRV8461
PRODUCTION DATA
PWM current regulation is based on the voltage sensed across the internal sense resistor of the DRV8461. Optional external resistors can be placed between the PGND pins and system ground (or in series with the VM pins) to sense the coil current, as shown in Figure 7-17. The DRV8461 has two PGNDA pins and two PGNDB pins - one pair for each H-bridge. So, the current of each stepper motor coil can be sensed separately by placing sense resistors between PGND pins and system ground. All the four VM pins are shorted internally - so if a sense resistor is placed in the VM path, it will sense the combined current of both the H-bridges.
The voltage drop across the external sense resistor connected between PGND pins and system ground should not exceed 300 mV. The sensed coil current can be processed to monitor motor health, or used to generate necessary signals in a field-oriented-control loop to improve overall system efficiency.
No current flows through the sense resistor during the slow decay, so the sense resistor conducts less than the coil RMS current. Place the sense resistors as close as possible to the corresponding IC pins. Use a symmetrical sense resistor layout to ensure good matching. Low-inductance sense resistors should be used to prevent voltage spikes and ringing. For optimal performance, the sense resistor should be a surface-mount resistor rated for high enough power.