Tool/software:
What is the best way to protect the chip from blowing up due to overload?
I was trying to establish the heatsink performance on our prototype board. The setup includes the prototype board connected to a 24 Volts 12 pole BLDC motor, speed =3600 rpm (no load) 3200 rpm (full load), continuous current rating of 8.2A. The part is operated in close loop mode, The registers on the MCT8316 are set as follows: Close Loop1(0x86) = 0x0e3a0200, Fault Config1(0x92) = 0x78f43025, Fault Config2(0x94) = 0x7147a009, GD Config1(0xac) = 0x1c440000. I initially ran the test with CBC current limit set to 4A (Close Loop2 (0x88) = 0x02a6e4b0). The speed was set to 100%, the motor reached the full speed under no load, then load was progressively increased. The motor stalled at about 3.2A I_Bus, CTL _FAULT register showed 0x80500000, the heatsink temperature was 118 F. I increased the CBC current limit to 6A (close loop 2 (0x88) = 0x02a6e4c8), Again the motor reached full speed under no load, the load was increased progressively until the bus current was about 5.6A, the speed dropped to about 1500 rpm. The motor ran for about 30 sec but never reached full speed, then the chip blew up. The control and gate drive fault status registers were constantly monitored but the CBC_ILIMIT, OCP, OT, OTW bits were never set. The chip never entered over current protection mode and shut itself down.
The prototype board follows the layout example shown in fig 11-1 of section 11.2 of datasheet. The thermal pad on the chip is soldered to a ground plane on component side which is connected to the ground plane on the track side via a matrix of PTHs. The heatsink is mounted on the trackside.