ITS724G diagnostic

Question

We are using two ITS724G devices from Infineon in one of our designs. We are now struggling with the diagnostic function and want to check if someone else have had the same problem and maybe have a good solution.

The problem is that two outputs share one diagnostic signal and the ITS724G device detects both short to ground/overtemperature and open load. See truth table:

Our problem is that we do not always have something connected to each channel. If one of the channels (channel 1) detects "open load" the diagnostic signal (ST) is always active and thus we can not detect "overtemperature" on the other channel (channel 2). We can get around this by setting channel 1 high and then detect "overtemperature" on channel 2.

We have tried to solve the problem by first doing an initial test to check which outputs are in use and if there is any short circuits. Then based on that information we try to check during runtime for open load and overtemperature on the channels that are in use. This is very tricky and there are many trade offs. We have seen that the diagnostic signal is not constantly low when overtemperature happens but is going low and high with a cycle time of 10 to 50 ms. Now we try to use this information to detect if there is a short circuit.

Is there any one else that have used the diagnostic signal on the ITS724G or similar component?

Answer 1

If you are not interested in the open-load alarm you can use a pull-down resistor on the output.
Quite high looks from the number in the datasheet, enough to pull 5uA to ground and keep output below 1.7V.

This will solve your problem of not being able to differentiate between short circuit and open load. You are right that short circuit will cause thermal cycles, the period and frequency depend on the load and ambient temperature. They require empirical determination.