TPS2660: eFuse RTN, GND and Input pins are seen shorted to each other

Hello User,

Welcome to E2E.

Is there a chance of VIN abs max violation?

Input voltage transients or surge or negative voltage which could violate the abs max.

Thanks 

Amrit 

Hi Amrit Jit

Yes, it may have exceeded abs max values.

I removed eFuse from the board and there is no short between GND-RTN-VIN pads of eFuse on the board.  Then I measured the eFuse pins on the air, there is still short between GND-RTN pins but surprisingly there is no short between VIN-RTN & VIN-GND pins anymore. Some 100's K and M in opposite direction is measured. I also tested GND-RTN in a diode test mode. It seen really failed. 

While eFuse mounted on the board VIN-GND & VIN-RTN was seen short, but after removed eFuse from board, VIN-GND & VIN-RTN is not seen short anymore in the pins of eFuse. Is this normal? How can be explained this short circuit is gone now?

Best Regards,

Hi Amrit Jit,

GND and RTN are separated in schematic. 

I measured the eFuse pins after fixing it on a paper. There is no short between eFuse pads in the board. I think measurements are proper. As I said before, I am surprised that GND-RTN short is still there in the IC pins, but no short between VIN-RTN & VIN-GND pins anymore. 

Board is working after mounted a new eFuse. 

Best Regards,

Hello Doner,

Sometimes failure signature erase with heat treatment during soldering.

Just curious to know if the same IC working after placing on board.

What's the test condition where device is failed?

Thanks 

Amrit 

Hello Amrit Jit, 

Actually, there was no short in the board after desoldering the failed eFuse. 

I will solder the failed IC on the same board and see the results. 

I think this thread is seen closed here. Let me know your e-mail, if possible, then we can talk about the test condition quickly. 

Best Regards,

Hello Doner,

I have opened the thread.

If you want to discuss privately, I have sent you a message.

Thanks 

Amrit 

Hi Amrit Jit,

I mounted the failed eFuse to the same board. Surprisingly, VCC-GND short came again. It is seen short again around 16-18 ohm, so we came to initial situation now. 

- I know there is no short between VCC-GND in the board. Because I have taken measurements from pads on the PCB when there is no eFuse. I also mounted a new eFuse and board was working properly. 

- I know there is no short between VCC-GND in the failed eFuse. because I took measurements pins of the failed eFuse on a paper. In fact, a permanent short circuit is seen between GND-RTN pins in the failed eFuse. 

But when I mounted failed eFuse onto the same board, now is VCC-GND is seen short around 16-18 ohm. what can be reason of this behavior? 

And I should say this: there are more than one boards where eFuse' GND and RTN pins are shorted to each other which are separated normally in the schematics. This can be root cause. What can be reasons of the GND-RTN be shorted? And when GND-RTN are shorted, can this lead a something unexpected results? 

Thank you,

Hi Amrit, 

Thank you for your reply. 

Normally, there was a 0-ohm as R1. (UVLO resistor). But after I mounted 110K as R1, now VCC-GND is seen ~110K. Board is now working properly with "failed" eFuse. So probably UVLO-RTN is shorted inside the chip. 

But I think that root cause of above is the short between GND-RTN due to some reason. 

Please note that, there is no TVS diode input and no schottky diode at the output of eFuse, and there is a common mode choke (500uH) and inductor (18uH) at the output of the eFuse. Could these have caused a GND-RTN short circuit inside the chip ? 

Thank you

Hello Doner,

Is there any possibility RTN pin abs max violation?

VOUT side since there are inductance, you should consider placing a Schottky diode for negative voltage.

How many units do you see such issue?

You can submit for FA where we can do Xray to find which block is damaged.

Thanks 

Amrit