TPS63020: latch-up and Enable pin not work

Hello Pawel,

Do you have any idea what could have caused the high output in the first case? As this device does not discharge the output when disabled (or during operation when PS is enabled), the output needs to be discharged by the load if it gets such high. The question is where is the energy coming from, charging the output capacitors to 6.1V.

The same is valid for the second case. The IC will not discharge the output when disabled.

Please observe the switch nodes when the output is such high. They are not allowed to switch in this case. If they are not switching, the IC is operating as expected.

I can observe that you have a discharge circuit R17 and Q4, but I wonder if there is maybe a problem with this one if the input voltage is too low.

Hello Brigitte,

thank you for reply, i dont wrote it in my previous post but i checked this. its are basics.

Our device is very simpe: battery powered MCU (MSP430 family) and GSM/3G communication module supplied by TPS step-up converter. Both ICs are connected via UART (2wire). There are not any other Voltages exists ( 3.6V battery and 4V TPS output).

So, i'm sure that TPS converter are not work properly and it was a source of 6V.
Below i add screenschot from L2 pin from TPS63020 when VOUT=6.2V.

In case of lath-up at Vout=4V L2 wave looks similar, with different voltage level. So it means that output capacitors are supplied from TPS IC only, and are dischargeing by GSM/3G module.

Additionaly 3rd case what i mentioned about (latch-up with Vout=0V) below are waves: 

And everything is fine (at all cases all sets) after battery reconnection, and sometimes this issue is back after some time (some time means minutes or hours it can't be measured precisely now). 

Hello Pawel,

I am sorry, when I reviewed you schematic yesterday, I misinterpreted the connection to PS/SYNC. You are right, then the output voltage never should fall out of regulation because even when the output gets too high, the converter should regulate it down.

You mention that you have these problems on all systems, correct? How many systems do you have? Did you test if exchanging TPS63020 solves the issue?

When you have a system that shows the issue again after re-connecting the battery, could you please check if the problem is gone when Q3 and Q4 are removed?

Where do you measure the ENABLE signal? Can you please check it again on the pin of the IC?

We have two different projects, both didn't have problems at prototype state. In both we use TPS63020 for provide power supply for GSM/3G modules but this modules are different in projects.
Problematic project was produced with over 100 pcs one moth ago, and there we didn't find this issue. Currently we produced around 30pcs and 28 of them have this defect. The second one of projects we produced small qty till now and last production was over 3 months ago.

Yes, like you suppose I use some wire to connect oscilloscope and I connect it at more comftible point, but also I checked ENABLE signal on IC's pin directly - signals are same.

Also yesterday I exchanged IC on defective sets but i'm not sure about results, becaue battery was discharged during this night. I can supposed only that the lath-up of DC/DC converter at 4V or 6V was happened and that was a reason of battery drain. I have to repeat this test with more samples.

Of course i will try also your suggestion about Q3 and Q4 and i will share the results.

Hello Pawel,

What is the difference between the prototype systems and the final systems? Maybe this differences help to identify the root cause of the issue.

Hello Pawel,

I haven’t heard back so I’m assuming you were able to resolve your issue. If not, just post a reply below (or create a new thread if the thread has locked due to time-out).

hello,

Problem is not solved yet,

I'm keep quiet because i don't have any breaking news. This problem is so complicated because this defects are not permanent. Many sets are fixed after supply power reset, rest of them are defective sometimes, sometimes not, and i can't find any rules.
I have one set with TSP63020 permanently broken: in this case ENABLE pin works fine but Vout=6.2V always (Vfb= around 0.7V and resistors are ok). It's only one pcs and probably it's efect of lathup with Vout over 6V by long time.

Now main question is: why TPS63020 don't respond for ENABLE singnal properly, and what's conditions are required to call this issue?

Hello Pawel,

I never saw TPS63020 not reacting on the enable pin, so I do not have any idea about the conditions that could cause this in your system. I only can try to recommend possible tests to find out what causes this issue or recommend a failure analysis of the component that is damaged or that is showing this issue stable.

If you want to do a failure analysis of the damaged device, please have a look at this website. I would encourage you to start such an FA, because it might give some information on the root cause.

Here some possibilities for checking out the root cause:

- Please share your layout and BoM. If you do not want to share it here, please send it to lbs_request@ti.com

- What is the difference between the prototype systems and the final systems? Maybe this differences help to identify the root cause of the issue.

- Is it possible that there is a problem with the connection of the FB pin in your system? Please check if you can observe a difference of the FB voltage when measuring it on the side of the package of the device (if you not already did).

- On systems that show this issue, please heat the device and all external components again to a temperature hot enough to melt the solder, then push all devices down on the board and check if the issue is gone then.

- Did you check if the problem is gone when you remove the load (if this is possible during operation)?

-Please measure in all 3 observed cases the EN pin, both switch nodes and the output voltage at the same time?

Hello Pawel,

Have you been able to get additional information with the above questions? Especially the difference between the prototype and the final system would be interesting for me.

What happens if you replace the ICs with new ones?

Hello,

Now I can share some info about reason of this issue, and now we can consider how to solve it.

About your questions:
There wase some differences between prototype and current project but all was at second PCB.
I will try to catch L1 and L2 signals related with ENABLE and share it by next post. Some of them are already shared by me previously.

Now the point of this post:
This issue happened only whed two conditions are exist: battery supply AND internal GSM antenna are used.
Unfortunatelly internal antenna is located near to the battery and TPS63020 IC (around 20mm distance to the IC with open space between them). Problem was never happened when we change one of this parts. At this project other kind of antenna is used in other variant - external antenna with 2 meter cable.

I supposed that there are some noises related to communication by GSM and nearly located antenna. You told that you don't saw device not responded to ENABLE, but maybe you have some knowledge about TPS woked in high electomagnetic field? Maybe our PCB layout should be redesigned to work properly in that conditions?

I attached here some screenshots of part of PCB layout related with TPS63020 IC. This system (device) have two PCBs conneted by standard 2 row pitch 2.54mm connector (located at top edge of my screenshot). On second PCB only one critical component is located, microcontroller whitch is source of ENABLE signal. Both PCBs are soldered to this connector and device can not be disconnected after soldering. So we can skip mechanical-connection issues.

 

 

Hello Pawel,

Thank you very much for sharing the results you have up to now in digging into the issue and for sharing the layout.

You mention the following:
This issue happened only whed two conditions are exist: battery supply AND internal GSM antenna are used.
Unfortunatelly internal antenna is located near to the battery and TPS63020 IC (around 20mm distance to the IC with open space between them). Problem was never happened when we change one of this parts.

As the problem is not existing when you are using the internal antenna, but not the battery, I think the high electro-magnetic field alone is not the root cause of the issue. The electromagnetic field should be the same, independent of the source, as I understand it. Please correct me if I am wrong.

So it seems to be a combination of the electromagnetic field and a floating GND connection, at least if the total system is supplied from the battery and you do not have another GND connection elsewhere. Do you agree?

When I have a look at the layout, it seems that the GND connection of the input capacitors of TPS63020 and the the GND connection of the bulk capacitors C1 and C3 is relatively weak. I could imagine that you get some GND shift between the battery and the IC when the high electromagnetic field is there.
If the GND shift is big enough, it might be possible that the EN signal and the voltage on the TPS63020 are shifted enough that it cannot enable the device anymore.

I do not know, if it helps, but you might check if a thick connection from the GND of the bulk capacitors to the input capacitors of TPS63020 make the problem appear less frequent (even a reduction points in this direction because it is almost impossible to solve a layout issue by adding some wires somewhere).

In general I would recommend the following, if you redo the layout:
1. Try to get all ICs (not just the TPS63020) as far as possible away from an antenna, or shield the antenna signal at least to the ICs with some GND layers (be careful, cuts in the GND layers might amplify the electromagnetic field, so try to not have cuts in the GND layers in the area of the ICs). I recommend this because ICs in general might be influenced by electromagnetic fields, not because I ever have seen an issue with TPS63020.
2. Remove the thermals when connecting to planes. Thermals increase the impedance and are in almost all production sites no longer necessary because the board is heated in an oven for soldering and not punctually heated. Please clarify with your manufacturer if thermals are necessary. If they are necessary, make them wider. They are very thin on your board.
3. Connect the bulk capacitors to the GND layer with a lot of vias.
4. Try to layout GND of TPS63020 the way that it has a good connection to the bulk capacitors, to the input capacitors and to the output capacitors. It is ok to use a GND layer for this, but I would try to keep the high current loops of the buck-boost converter on the top side via a GND layout that is lower impedance than a number of vias.