TPS26600-02EVM: reverse input protection

Hi Dmitry,

I will check and get back on this.

Regards

Kunal Goel

Thank you. Please notice that there is a thread entitled "TPS26600-02EVM: breaks from reverse voltage" that describes my situation exactly, except that I tested with -10V rather than -12V. And there was no resolution documented in that thread. Does that mean that the datasheet is wrong to suggest that efuse can be deployed without a diode on its input where reverse input polarity is possible?

I am checking on this. Sorry for delay. 

Hi Dmitry,

Could it be possible that eFuse was already damaged before you did reverse polarity test?

Can you try on other channel and this time disconnect FLT from VIN?

Regards

Kunal Goel

efuse worked in the test immediately prior to that, those tests were done with direct input polarity. Both undervoltage protection and overcurrent protection worked as expected. After those tests input wires were flipped and short developed within 3 seconds of applying power with flipped wires. 

Yes will try on the other channel without FLT jumper.

Here is what I tested:

1. desoldered that failed efuse and replaced with a fresh chip. Checked that short is gone from the input- confirmed.

2. applied 10V and confirmed that efuse works, lowered voltage below 10V and confirmed that undervoltage protection works. During this test I saw green and then red LEDs light up, so all good here.

3. removed J8, reversed input wires and applied -10V- there is zero on output, no short on input, so reverse input polarity protection works.

4. reinstalled J8, applied -10V- same, all good.

5. flipped wires back to normal polarity, applied 10V, confirmed that efuse is operational- all good.

6. reversed wires again, removed J8, applied -26V- all good.

7. up to this point I used the same load meter as in the original test but a different power supply. So brought back original power supply, reinstalled J8, applied 10V- all good.

8. removed J8, reversed wires, applied -10V from the original power supply- no issues, all good.

9. reinstalled J8, applied -10V from the original power supply- still all good.

10. flipped wires back to normal polarity, applied 12V and let it sit for a few minutes with 2.2A current.

11. reversed polarity again, applied -12V- still good, with J8 installed.

12. final check- restored polarity, applied 12V and 2.2A, confirmed ok, increased to 2.23A and observed overcurrent protection kick in with red LED lighting up.

So here is my question based on all of this- could it be an assembly defect of eval boards for this RHF chip where RTN got shorted with excess solder to GND pin either by shorting pin 16 to pin 17 or to the pad, thus disabling reverse protection? Would that result in the symptoms that I described- a few seconds of reverse voltage passing through followed by damage to efuse with short on its input?

I think GND to RTN short would explain why both my board and the board from the other thread had the same disastrous reverse input behavior. So my second question is whether you can check regarding eval board assembly protocol- was there QA done to make sure RTN and GND are not shorted on the RHF side on assembled eval boards?

Hi Dmitry,

I will check and get back.

Regards

Kunal Goel

Hi Dmitry,

You observed this issue on two EVMs?

Regards

Kunal Goel

I observed on one board. But Shai from "TPS26600-02EVM: breaks from reverse voltage" thread observed exactly the same issue on his board. So between me and Shai we have observed it on two eval boards.

Hi Dmitry,

Let me check on this.

Regards

Kunal Goel