Hello all,
my goal is to design a very reliable PCB to test a product (motor). The INA239 measures the bus voltage (48V) and current (Imax 20A) going inside the motor. We are using an industrial power supply to simulate the battery, so our use is similar to the Figure 8.2 of the datasheet, but only one direction to the load, no charger needed. We use a second INA239 for the auxiliary input 12V, Imax 2A (LEDs, communication, etc).
My first design works fine, but the INA239 (on the 48V bus) eventually breaks when there is something wrong with the product. We had one board working for around 4 months without problem and in one week 4 chips have broken. The INA239 gets really hot and the resistance between 3v3 and GND are close to 0. The worst case the SPI lines got affected and also burned the MCU. I guess for this an SPI isolator will do.
The main problems about the product I can think are: short-circuit of the 48V and GND lines; 48V and GND lines switched during the motor assembly; bad firmware - short circuiting the H-bridge; motor back-emf.
Many times the board can detect the short or that something is wrong or the MCU watchdog kicks in opening the switch. Other times don't and the chip breaks, which worries me.
As protection there are TVS diodes on the line and the mosfet switch is programmed to open when the current passes 19A. The typical current at max power is around 17A. I have added screenshots of the system.
I know that the pcb and the protection of the INA can be a lot improved, as I am not an experienced PCB designer and is my first time using the INA239, every help is much appreciated.
Thanks,
ps1: the alert lines are open, cause the MCU run out of pins. I don't belive using it, will make a lot of difference with our issue, since the chip is instantly burned.
ps2: the ground lines (product, PCB, power supply) are tied together with a distribution block inside a panel. The external diode is connected directly to the 48V / GND connector of the product.