Tool/software:
Hello,
based on a similar setup of my recent post (https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1377231/lm5069-no-latch-off-after-high-overcurrent-load)
i have a question regarding the effects of attaching charged high capacitances to the output side of the LM5069: By coincidence we found out that attaching a large charged Capacitor at the Output while the input is open leads to desctruction of the IC.
Test Setup (see picture below):
- Input Line is open and at 0V to GND - nothing connected here
- C_ext (14mF) is charged to 48V and attached to the Output via mechanical switch
When the mechanical switch is closed we see that the LM5069 IC is damaged and the OUT-Pin is burned. My thoughts about this:
- When closing the mech. Switch there will be a high inrush current from C_ext to C1 and C2. A current to C1 higher than approx. 100A would result in a Voltage drop of over 0.3V along the shunt resistors, meaning IN and Sense and exceed the max. specs -> if this is true, why is the OUT pin burned? If this is the reason of the failure, do you see any other solution than adding a Back to Back FET in series to Q1 to block reverse currents?
- Voltage spikes might occur on the Out and IN line due to bouncing of the switch and oscillation between capacities and line inductance (Output to C_ext: approx. 1m lab wire) -> these should be suppressed by D2/D1 and negative voltages swings should be blocked by D3.
- Attaching a regular power supply with 48V at the Output and switching on does not result in destruction of the IC. So it must have something to do with high voltage transients or inrush currents
Do you have an idea what could result in a short circuit current through the OUT pin?
Unfortunately, i dont have measurements available for this so far and before burning the next sample PCB i need to have an idea where to look at.
