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TPS65023 failiure - very high current to DCDC1

Daniel Ciu
Prodigy 240 points
Other Parts Discussed in Thread: TPS65023

Hi,

We're having a problem with a TPS65023, it worked fine for several days (including temperature tests) and at some point out of the blue it failed.

The component was hitting our PSU's current limit and heating to temperature of 130deg celsius, it seems like the over current is going into VINDCDC1.

We removed the component from our board and mounted it on an EVB, when all the regulators and bucks are set to off the current is hitting 0.8A (it starts with about 0.3A and after several minutes it reaches 0.8A and heats up quite a lot).

DCDC2 and DCDC3 seem to be working fine, DCDC1 is quite weird, if we enable it the current jumps to our 1.7A limit and the output seems to be 1.2V (as it is programmed to be), we didn't want to increase the current limit any further because we didn't want to burn the component.

When DCDC1 is off the output voltage of that buck converter is about 1.4V and the pin seems to behave like a linear regulator when we apply some load.

the component responds to I2C transactions (reports power failiure) and the LDOs seem to work fine.

We're unsure as to what part of the device failed, what could be drawing the extra current? and how does it change when we turn the DCDC1 converter ON?

What could have caused this failiure? we haven't been able to recreate it on other components (we managed to do some damage by temporarily shorting DEF1 to VCC, the supply current increased permanently by 400mA but we're not seeing any of the other weird behaviours so the failiure mode must be different).

Regards,

Daniel

  • 0
    TI__Genius 16870 points

    Hi Daniel, 

    What is your load? Can you send scope shots of the SW node, Vout and inductor current for VDCDC1? It would be best if you can reproduce the failure but, if you can't be sure to include a working prototype too for a base line. Also take a shot of the failed unit's enabling: include the EN, SW and Vout for VDCDC1

    Do you have anything that could be back biasing the VDCDC1 Vout rail from your load? What is the temperature test range that you did on your prototype before the failure? 

  • 0 in reply to Michael Green
    Prodigy 240 points

    Hi,

    The load on the board is about 1A max from that converter, I'll try to get the scope shots but it might take some time.

    The component is currently on an EVB connected to a tester and we can see the failiure at all given states (with load, different supply voltages, etc), on the board the component was biasing the da-vinci core only so there isn't anyting that could've back biased the converter.

    The temperature range was -20 to 70 but the problem itself started when the board was at 25degrees.

    What is the ESD rating of the component? we haven't been able to find it in the datasheet.

    It seems like the PMOS of the component suffered some damage but the NMOS behaves strangely as well, we've seen some overshots and undershots at the inductor pin (+7, -2V on the board for about 5ns), could that have caused this?

    Regards

     

  • 0 in reply to Daniel Ciu
    TI__Genius 16870 points

    Hi Daniel, 

    1. I will wait for your scope shots. I can't really debug your problem without the this data. 
    2. Please check this app note http://www.ti.com/lit/an/slva273/slva273.pdf. Verify that you are indeed power sequencing correctly and in line with what this document reports. Power sequencing is critical and can cause problems if handled improperly. 
    3. The temperature testing does not look like the problem. 
    4. ESD: Please see this post: http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/t/100380.aspx
    5. For your last question please see this app note: http://www.ti.com/lit/an/slva494a/slva494a.pdf