EVAL-Board DRV8323RS: Power Input wires VM and VDrain blow up.
We use the driver eval board to drive a 7 pole pairs BLDC motor (max power approx. 340W). The commutation is done by a CPU with implemented current controller. We are using the board in 6xPWM mode. All internal control registers of the DRV were left on the default values.
Due to errors in the software, the commutation sequence didn’t start right away after power on, because no interrupt from the HALL sensors occurred. So, the BLDC was standing still and the current gauge showed 0,04 A (40mA nominal driver board current), since there was no updated commutation pattern from the CPU.
Meanwhile the current controller recognized the zero current and tried to reach the desired current by increasing the duty cycle. Soon the duty cycle reached 100%, but was not put through to the driver board due to missing interrupt in the CPU. Then, as I poked the BLDC to trigger an interrupt, suddenly a firework began. The PCB routings V_M and V_DRAIN completely burned away and also the case of the driver shows some burned spots. See the marked positions in figure 01 below.
The source voltage was set to 28V and a current limiter was set to 1,6A and DIDN’T trigger during the whole event (!).
On a second, identical driver board, it accidently happened again. The same conditions. The same spots burned away.
See Figure 1 in the attached file.
Due to project specification, we reworked the board slightly. We removed the three low-sided shunts, bridged the shunt terminals and placed only one shunt on Phase A (0,011 Ohm instead of 3 x 0,007 Ohm) to measure only one current value (see the pictures below). Connection was tested and was also working well before the above-mentioned accident.
Further, the soldering pads beneath the screw output terminals for the phases on the first board were damaged due to vibrations during former testing and needed to be bypassed from the MOTA, MOTB and MOTC test pads (see the pictures below). These connections were checked after soldering too and were also working well before the accident. The second board had no damage on any of the terminals.
We don’t understand what can be the reason blowing up the power supply wires on the DRV8323RS. If there was an extremely high current because of the 100% duty cycle, wouldn’t it blow up the MOSFETs or the shunt in the first place? A high Back-EMF blowing up the DRV because of high voltage peaks on the measure inputs (such as SHA, SHB and SHC inputs) seems also very unlikely to us, since the BLDC didn’t even spin up.
We ask the community about similar experience with the Eval-Board and the component DRV8323RS. Is there any explanation what happened?
In the attached file you will find photos of Board 1 and Board 2.
Board 1 is shown in Figure 2, Figure 3 and Figure 4.
Board 2 is shown in Figure 5, Figure 6 and Figure 7.