Hi,
We designed a driver circuit with the DRV8871 which drives a high inductance coil around a ferrite magnetic core. There is a secondary coil wound around the same core. The use-case for this product is to have a cold redundant coil, i.e the two coils (primary and secondary) will not be driven simultaneously.
What we are getting is that when we drive the primary coil while the secondary coil is unpowered, the DRV8871 gets damaged, the DRV8871 IC on the secondary PCB gets damaged.
At this stage, we have no working, workaround. We use the same PCB on the single coil design, this design seems to be working okay. What we tried is to insert a 45V tranzorb between OUT1 and OUT2, to mitigate voltage spikes the secondary coil because of a transformer effect.
initially, it seemed that this gave better results but we still have failures. Maybe firstly, can you use this IC the way we are trying to use it ? i.e to drive a inductor of 1.326H
I think I need to explain our grounding scheme. PGND and SGND are connected together on the power supply, i.e they are connected with an essential short. We connected the TPAD of the IC to our chassis ground which is also connected to PGND and SGND but through the mounting bolts which hold the PCB to the Aluminum Foot. The ALU feet which are chassis ground is connected to PGND and SGND via the mounting structure i.e Chassis GND is connected to PGND and SGND through a high resistance path.
Something interesting we picked up, is when we place (solder) the DRV8871 IC to the PCB and measure the resistance between TPAD and GND of the IC. Before powering the PCB, we measure around 2Meg-20Meg ohm's but when the DRV8871 IC is broken/stops working correctly this resistance drops to 1.5Ohms. We set the current limit on the DRV8871 to 360mA on our design, I just confirm that when the IC stops to work the output of the bridge is not active( it does not switch the outputs anymore)
Hope you can help with this issue.
