TPS25947: Circuit Breaker Behaviour

Hi Bakker,

I see that the Vout is not equal to Vin in the last waveform and it looks like the device did perform some action on it.

Can you share the setup details and load details. Also if you are using e-load, please mention the mode you are using and how are you applying the ramp rates. 

Best Regards,
Arush

Hi Arush,

I will get a scope capture with the Vin included.

The e-load was set to CC mode and 20A in all cases. The soft start current ramp rate was varied for each of the three tests shown.

I also measured the voltage on the ILIM pin, and it matches the output current shape, greatly exceeding the expected trip voltage in the last test.

Kind regards,

Rob

Hi Rob,

It would be best if you can test the device in CR mode of e-load. The device when performing circuit breaker/current limiting acts like a current source and using the CC mode of e-load is like connecting two current sources/sinks of different value in series. This results in misbehavior of devices.

When using CR mode, you can sweep the resistance value to create different sweep case for Iout or use dvdt pin of device for different output voltage slew rate. 

Please share with me if this resolves your issue. 

Best regards,
Arush 

Also, can you accept my friend request. That will enable E2E DM option. 

I have repeated the test with the e-load in CR mode, please see scope capture below.

Vin and Vout are also included.

It seems that we are having the same issue as before with the trip current.

Hi Robert,

I am not fully sure why this is happening as you are seeing no issue with 50mA/us (slower) and 300mA/us (faster) and seeing issue with 200mA/us. I believe, this should not depend on slew rate.

In CR mode, how are you sweeping the load? 

Let me also discuss this once and get back to you on this by Tuesday EOD. 

Best Regards,
Arush

Hi Robert,

Can you probe itimer pin along with Vin, Vout, Iout. Similarly probe dvdt pin.

Is this issue repeatable

a) on same ic device

b) across multiple ic device

Best Regards,
Arush

Hi Arush,

I have managed to replicate the issue on the TPS25947EVM dev board.

Please see the waveforms below:

The dev board was configured as below:

In CR mode, the e-load has a soft start function which allows the load to be swept.

Thanks,

Rob

Hi Robert,

We generally don't do current ramp rate testing as we don't expect any different behavior at different ramp rates. In your case also, you do not see any issue for fastest and slowest ramp rates. 

I will have to replicate this on bench. I can back to you on this by end of next week. 

FFT internally work with a comparator across FET Vds. When the current*ron drop is greater than certain threshold, it trips the device. 

Best Regards,
Arush

Hello Arush,

Do you have any updates on this fault?

Thanks,

Rob

Hi Arush,

Did you manage to replicate this behaviour on the bench?

We are still facing this problem on our side and cannot find a solution.

Cheers,

Rob

Hi Arush! 

Just checking in on this thread. Any luck replicating this on the bench?

Thanks,

Rob