TPS281C30: How to protect the VIN of this component in the case of a Vout-to-GND short?

Hi Sravya,

Thank you for the response! So I currently have the following set up for my voltage supply which is my VIN:

The short would be 100ohms and under, do you think this should gett the "Perm_Prot_24v" line high and protected while Vout is shorting and the HS switch is detecting the short to switch off?

Thank you

Hi Sravya,

So does that mean the capacitor will only shortly delay the power prot 24v shorting? As it doens't detect the short due to the capacitors?

I did a test of what the protected 24v line which is the blue trace.

Thanks!

Hi Matthew,

I am unable to visualise the schematic of where you are shorting. Can you please give the complete schematic of how the HSS is used and where you shorted the output. Thanks

Hi Sravya,

Here is a system level view of where I am shoring and where my scopes probe is for the blue trace above:

And here is a snippet from the schematic of the device that should have the protection but it does not provide any hence why I am looking for a new component for this application:

So the TPS281C30 would but to replace the BTS441RG. As mentioned I need that Perm_Prot_24V to be protected at all costs and not drop the voltage if the output (Prot_24V) shorts to ground. This is because the Perm_Prot_24V line holds important relays closed.

Does that make sense?

Thank you!

Hi Matthew,

We have couple of questions.

1) Did you put your current compliance of the supply correctly? It should be greater than what the load/short/device current limit is asking for?

2) How much input cap do you have on the perm_prot_24V line and before the two oring diodes that you have?

3) If you had a 100uF cap on the perm_prot_24V like you showed, the cap should be discharged slowly at 2.5V/1ms which doesn't seem to be the case from your waveform.

4) Why are you looking for TPS281C30? Do you have a 60V requirement at supply? If I understand your application correctly, you will have to pick a device with current limit range below the current compliance of your supply. Otherwise, supply will always collapse.

Thanks,

Sravya

Hi Sravya,

1) My power supply only supplies a Max of 3.1A so nowhere near this HS's current limit. I inherited this design/board so I am not sure why such a large component was specced.

2) I have 2 seperate 28v supplies that have a 100uF capacitor before going through the diodes and being joined on the board

3) I have both connected as shown, both inputs were going to the same bench supply for this test. Would that still be the case in a short circuit scenario?

4) I was looking for a lower current HS switch for this use case and came across this component. I am not sure what else would be a better fit. Even you have any other suggestions that that would be really helpful, I was looking for the following:

• 6-32V voltage supply to HS
• Short circuit protection if Vout shorts to ground
• Enough current to allow Gigavac GV241MAB contactor to close from further up HS switch - Datasheet says max inrush spike of 3.6A and transients of +/-60V

I hope they make sense! I really hope what I am trying to do is possible.

Thanks again for the support, I really appreciate it!

Hi Matthew,

If your supply max compliance is 3.1A, how is the contactor given the excitation current of 3.6A. What is the current limit setting you have given for TPS281C30? If you are choosing TPS281C30 current limit to higher than 3.6A to allow the excitation current, then supply will collapse during output short because current will be limited to >3.1A.

Apologies I mixed that up a bit there I think! I think that the max pick-up current is probably at the min pick-up voltage as I assmuse it is calculated due to power if that makes sense? Here is the datasheet to see if you agree with that:

If what I am thinking is correct then the lowest voltage I would ever see that operating at is 12V which is 2.55A if I used P = V*I (8.5V*3.6A = 30.6W) to get the power that the pick up values infer. So If I specces my resistor to make my current limit between 2.8A-3A then would that pick up the short before my supply collapsed?

Apologies if any of these are stupid questions!

Hi Sravya,

I will ask the manufacturer to get a value of max pick-up current for 12v and above. If that is below the power supply then maybe we are on to a winner.

Lastly can I just confirm that the following scenario is possible with the TPS281C30:

1. Max current load is 2.5
2. Power supply is max 3.1A
3. TPS281C30 has resistors setting the current limit to 2.9A
4. 24V supplied to VIN of TPS281C30
5. TPS281C30 is switched on from uC signal to supply 24V on Vout
6. A short occurs over a component connected to Vout and ground
7. Voltage will lower but the capacitors will keep VIN active enough to not drop the VIN supply
8. TPS281C30 will detect short circuit and open switch and closing odd Vout
9. VIN remains active and uC detects fault status of TPS281C30 and switches off HS

Does that sound right? The bit I am unsure of is between steps 7 and 8. If the capacitors are holding the voltage for a few ms then will the current be high enough to trigger the short circuit detection beforfe the caps make VIN collapse?

Thanks again for all the help, it has been really useful!