• State TI Thinks Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 3 answers
  • Subscribers 62 subscribers
  • Views 384 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS43060: Pgood is not pulled low when EN is low.

user5874164
Prodigy 90 points
Part Number: TPS43060

Hi, we have a small problem with the PGOOD signal.

We are using the TPS43060 in a 12V to 18V boostconverter. The PGOOD signal is connected to a microprocessor and to 3.3V through a 100k pullup resistor. 

The EN pin is connected to the same microprocessor with a 10K pulldown resistor. 

The datasheet says: "The PGOOD signal is also pulled low if the EN voltage or VIN voltage is below their respective voltage thresholds" 

Does this mean that whenever EN is low, PGOOD should also be low? 

Some time during startup it the PGOOD signal is not pulled low, even though the EN signal is low. This does not happen all the time, and is quit hard to reproduce: We have not found out exactly what triggers this behavior. 

We have also tried to disconnect the microprocessor from the PGOOD signal, leaving only the pullup, and we are still able to get PGOOD to be hight when EN is low.  

  • 0
    TI__Guru 68495 points

    Hi User,

    According to the datatsheet, PGOOD pin is an open drain pin.  If the device is not properly biased, the open-drain FET may not be turned on, this leaves the pin an high impedance and the external pull-up can show it at high voltage.   Only when the IC is properly biased (VIN is in the operating range and VCC is established), then the internal logic can work properly, and the PGOOD can be used to serve as the power good flag.

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 90 points

    When EN is low, we are measuring 0V on VCC. 

    This seams to be normal operation, 

    "It will turn on when the VIN voltage exceeds the typical 4.1-V UVLO threshold and the EN voltage exceeds the typical 1.21-V enable voltage threshold. ... When both thresholds are exceeded, the VCC LDO output comes into regulation."  - 8.4.1

    Does this mean that PGOOD will not be reliable when EN is low? 

  • 0 in reply to user5874164
    Prodigy 90 points

    correction, VCC is not 0V. When EN is disabled, VCC slowly decreases from 7.5V to 1.8V. 

  • 0 in reply to user5874164
    TI__Guru 68495 points

    Hi User,

    The PGOOD control circuit does need some voltage on the VIN pin to function.  When EN is low to disable the IC, the PGOOD will be pulled low if VIN<5V in all worst case conditions (including hot).  At room temperature, of lower, the needed min VIN is about 3.5V to have PGOOD in function.  So, in your case of VIN not lower than 12V, the PGOOD will be low if EN is low.

    Hope this clarifies. 

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 90 points

    I made some plots to better show what is happening.

    I only have a 2 channel oscilloscope, so i was not able to capture all signals in one go, but i tied to be consistent on all the plots. 

    What I am doing is that i am running the booster normally, and then turning setting the enable pin low. After approximately 7 seconds the PGOOD signal turns on again, without me changing the enable signal. 

  • 0 in reply to user5874164
    Prodigy 90 points

    I did some more testing. 

    We had an old similar board of the same type that does not have this issue. 

    I tried to desolder the booster chip from one old an one new board and switched them around so a new board got the old chip and the old board got new ship. 

    When i did this the problem moved with the new chip. The old board now got pgood problems, and new board works fine. 

    Can it be that there is some difference between different batches of chips? 

    here is the markings on the top of the chips i tested. 

    good chip: 

    43060

    ti82i

    avs8

    bad chip: 

    04060

    ti85i

    cgot

  • 0 in reply to user5874164
    TI__Guru 68495 points

    Hi,

    This is interesting info.  Although I don't think there is any design change between the two devices, I will ask our design team to confirm. 

     Is it possible that the bad chip was damaged somehow?  Do you have other ICs from the same batch to test? 

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 90 points

    Hi again,

    Did you hear back from the design team? 

    We are seeing this problem in a large number of chips (more than 20). I have not been able to good identify the batch of the others bad chips, but i do not think they all has the same marking. 

  • 0 in reply to user5874164
    TI__Guru 68495 points

    Hi,

    Yes they don't have any design change since the device was released.  Mostly the IC was damaged somehow during handling.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    TI__Guru 68495 points

    May I assume the issue has been resolved so I can close this thread here?  You can always re-open it by adding a new post.

    Thanks,

    Youhao