Tool/software:
Hi,
I am presently building a 28V 60W BLDC drive using DRV8306. The basic functionality tests viz., slow start, run at full speed, etc. with the 60W motor connected to a fan load using DRV8306 was initially validated. The I/P PWM signal to the PWM pin was provided using LTC-6992 (PWM modulator). The underlying schematic for the same is given below for your reference.
I tried to probe the dc bus line (+28V) at the juncture of turning off the 28V power supply while the motor was being run at a fixed speed corresponding to 70% duty ratio of the PWM. I am observing huge spikes on the DC bus line which is connected to the VDRAIN and VM pin of the DRV8306 as well which is as high as 66V (probed results are added below).
Fig. 2 DC bus waveform when the power supply is cut off while the motor is running at 70% rated speed
Fig. 3 Selected section of the DC bus waveform when the power supply is cut off while the motor is running at 70% rated speed
As this voltage spike exceeds much above the absolute maximum rating of the DRV8306, I surmise the DRV8306 may be eventually subjected to a failure in periodic runs at these conditions. I request you to suggest a way to avoid the spikes in such scenario.
Thanks & Regards,
Pratibha Naganathan
