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.

TPS65105: TPS65105

Part Number: TPS65105

Hello, 

I am using TPS65105 regulator in my project and now i am facing the issue. I want 11V in AVDD side but i am getting a voltage drop from 8V to 4.91V, whereas, VGH, VGL voltage i am not getting as expected. It is coming nearly 0v. please help me out as it is very urgent.

I want the voltages as follow,

V01 = 11V,

V02 = -6.8V

V03 = 20V

VCOM = 3.8V

Attaching the schematics for the reference

  • Hello Ashwini,

    Can you please elaborate on what you mean by "i am getting a voltage drop from 8V to 4.91V"? Your input supply seems to 5V so I am not sure what you mean by voltage drop from 8V to 4.91V.

    Is the boost converter switching at all?

    Can you please attach scope plots of input supply (VCC_5V), boost SW node (AVDD11_IND), boost output (AVDD_11V) and VGL_-6V8 all four traces at the same time? Please capture these scope plots at power ramp up and you can set the trigger to rising level of VCC_5V.

    Another scope plot with (VCC_5V), boost output (AVDD_11V), VGL_-6V8 and VGH_20V all four traces at the same time and triggering on rising AVDD_11V

    These scope captures should help us determine what may be going on.

    Kind Regards,

    Liaqat

  • Hello Liaqat,

    I am getting following voltages,

    AVDD_11V = goes to 13.5 and settles to 8.6V

    VGH_20V =  voltage is coming in mV arround 250MV

    VGL_-6V8 = voltage is coming in mV arround 200MV

    VCOM_3V8 =  0.67V 

    I even measured feedback voltages, Below are the voltages what i am getting

    VFB1 = 0.5V ( It shows 1.53 to 0.61),

    VFB2 = 1.47V

    VBF3 = IN mv 

    these voltages are not matching with datasheet.

    I will share the scope image shortly.

    Can you please check the schematics ..

    fyi we are not using linear regulator for 3V3. so made the transistor DNP. and connected the pins as mentioned in datasheet.

    Regards,

    Ashwini 

  • Hello Liaqat,

    Please find the below scope snaps,

    Please check and give suggestions.

    Regards,

    Ashwini 

  • Hi Ashwini,

    It appears that boost is not reaching to its regulation level at startup. VGL and VGH only start ramping up once boost is in regulation so that this the reason for VGL/VGH not starting. Is the boost voltage of 8V with load connected? If it is with the load connected can you please disconnect the load and see if boost is able to achieve proper regulation to 11V?

    The switch node waveform appears to be unstable but this could be due to insufficient sample rate setting of the scope. Can you please check SW node waveform again to ensure that it is repeating stable waveform of fixed frequency?

    I had already reviewed this schematics earlier and schematically I did not see any problem. So I am puzzled as to why boost is not able to achieve regulation.

    Could it be some board assembly issue? How many boards have you built and do all of them exhibit the same behavior? You will need to debug further. Please do let me know the results of your further debug.

    Kind Regards,

    Liaqat

  • Hello Liaqat,

    Thank you for your reply..

    Yes it was an assembly issue. It is working in the other boards.Some caps and resistors were mounted wrong in it .

    Now all voltages are proper and display is working too..

    Thank you for your support..

    Best regards,

    Ashwini Rajesh Kamath B

  • Hello Ashwini,

    You are welcome I am glad that your design is up and running now.

    Kind Regards,

    Liaqat

  • Hello Liaqat,

    Out of 7 boards assembled 3 are working with perfect voltages and rest 4 boards are showing 9V  at AVDD_11V point, 

    I am not getting 11V at the main boost regulator side and even other voltages like Vcom, VGH , VGL are in mV range even after checking all parts in the board. 

    Voltages show 11V and drive low to 9V and then all other voltages are not at all coming even after the debug .

    so can you please suggest what affects the main boost regulator to get proper voltages at the output side and what is the main thing i should check for the proper 11V voltage at main boost regulator side.

    Infact what is the main thing that affects AVDD_11V voltage?

    can please suggest what to check in the circuit, all 4 boards have same issue and we are not able to figure it out.

    Thanks & Regards,

    Ashwini Rajesh Kamath B

  • Hello Ashwini,

    If 3 boards are working and the other 4 are not working, I could only think of board assembly issues to be the problem. I would suggest to double check the boost resistor divider values (R117, R126, C111) and the REF capacitor C70 value. Remember that VGH/VGL will not come up unless boost is in regulation so please focus on double checking assembly values for boost circuit.

    Kind Regards,

    Liaqat

  • Hello Liaqat,

    Vref Voltage is coming properly and FB1 voltage is coming as 0.9v in non working board and 1.14V in working board.

    we changed those values again and checked it is the same issue. Any other way to debug this issue ? 

    Boost regulator is going to 11v and coming back to 9v nearly ..what may be the issue for this? 

    please give your inputs as it is high priority for us..

    Regards,

    Ashwini

  • Hello Ashwini,

    Since some of your boards are working where as others not and since you have already double checked component values, the only thing that I can think of is perhaps that the exposed center pad of the TPS65105 device may not be soldered properly. This center pad needs to be soldered to GND copper and if the connection is not solid, it is possible to have voltage offsets. You can try demounting the TPS65105 device on a non working board and remount it to see if this resolves the issue.

    Kind Regards,

    Liaqat