Tool/software:
Hello,
a LM5066i is configured with a 4 mOhm shunt resistor, RCL1 set to 10 Ohm and RCL2 set to 1 Ohm is used. 26 mV is used as reference. According to the TI excel calculation sheet this shall result in a current limit of 6.4 to 7.9 A.
I modified the sheet so it takes the tolerances of the resistors into account, which will widen the current limit range to be expected to 6.3 A to 8.1 A. This is of course only possible if all tolerances of the LM5066i, shunt and both parallel resistors are on their worst case tolerance limit, which is very unlikely.
But still, the trigger current of the circuit breaker on multiple boards with this circuit is hardly above 6.3 A but even below that. 33 units have been tested with these results:
- The LM5066i on 9 boards opens the circuit breaker at a current below 6.3 A. Lowest was 6.20 A.
- On 16 boards, the circuit breaker opens at a current between 6.3 A and 6.4 A
- Highest possible current was 6.6 A on only one board and ~6.5 A on all the other 7
So ~75% of those boards do not met the calculations of the TI excel calculation sheet. Including the resistor tolerances, still ~25% of the boards are out of the calculated current limit for the circuit breaker.
How can this be? Why is the actual circuit breaker current below the calculated values?
Best Regards,
Christian
