TPS560430: Circuit behaves as if there is short but nothing burnt

Hello,

Your IC may be damaged after enduring such a  large current draw, if possible can you try replacing the Cboot from 1uF to 0.1uF as per the datasheet recommendation and retest using a brand new IC. If this does not result in a change in operation, then there may be a short somewhere that you can't see.

Other than the Cboot, I do not see anything wrong with your schematic.

I can also review your layout if you'd like as well.

Regards,

Harrison Overturf

Hello Harrison,

I found the problem over the weekend. I brought the wrong component. I brought TPS560430X3FDBVR which apparently is a 3.3V fixed regulator version. Because of the feedback resistor, it gave out higher than 5V which might have blown the components after the regulator which resulted in a short.

I need to buy TPS560430XFDBVR‎ which is an adjustable one. The circuit around it will adjust the output to 5V. This one will work for my circuit. 

Please let me know if you agree with me? I would use a second opinion. Here is the picture which proves my theory: 

Hello

So I brought the correct component and soldered on a brand new board. The same thing happened. Now sure why? There's literally nothing connected after the output capacitor of the regulator. It's impossible to have a short. Seems like there is a design flaw that I can't see. Can anybody see what I can't see?

Hi Varun,

Can you determine if it is VR5 or VR3 that is shorted? Are they both populated? Is anything else populated that is connected to 12V? 

Can you try removing VR3 and see if the short goes away?

I notice from your schematic that you have several PWR_FLAG symbols. What do these connect to?

Regards, Jason

Hello 

VR3(3.3V linear regulator) is not populated. Only VR5 (Switching regulator 5V) and its components to get 5V are populated. It's impossible to have a short as it's not connected to anything. 

Power flags are representing whats the voltage at the point and going forward. The only source of power is the 12V which will be reduced to 5V and 3.3V subsequently. Currently, I've connected the board to a 5V (DC power supply) and limited the current to 1A. The power supply is giving out 1.3V only. It increases slightly when I increase the current limit to 2A but there is smoking coming out. This leads me to believe that there is a short for sure. Something is wrong with my circuit. I'm even thinking of going back to a 5V linear regulator. I used them before and dint have a problem. This is my first experience with a switching regulator.  

Please look at the attached image. The components inside the yellow highlighter are populated on the board. Nothing else. 

Hi Varun,

It sounds like the board itself may have an issue.

Is it possible that the PWR_FLAG nodes may be shorted together?

Have you tried removing VR5 and applying power? Is there any current draw?

Regards, Jason

Hello 

I'm not sure if the power flags are causing an issue. It never happened before though. On one of my other boards, I had 24V, 12V, and 5V. No power flag short. The only difference is, they all were linear voltage regulators. 

I removed the VR5 and the DC power supply is not drawing any current. So it's an open circuit. No short till VR5 (not much there anyway). 

After VR5, there is a short because that's when the problems arise. but I didn't connect anything after VR5 except the components recommended by the datasheet of VR5 for 5 V output. 

So you think I should just ditch this board and make a new one with 2 linear voltage regulators? 

Varun R

Varun,

If there is a short on your board, switching to linear regulators will still have an issue.

Have you tried checking for shorts using a DVM? You can do a ohm check from 12V test point to other points on the board near. 

If you want to discuss ideas offline, you can contact me directly at jarrigo@ti.com.

Regards, Jason

I just sent you an email. 

Varun R