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TPS552882-Q1: Not working as designed

Saira Shaikh
Prodigy 170 points
Part Number: TPS552882-Q1

Tool/software:

Dear Team,

Greetings of the day!

I have designed the TPS552882-Q1 Circuit for the following parameters:
Input: 10-12.6V 
Output:12V 
Current requirement: 0.05-2A

Custom Board 1: 

The circuit seems to work at the beginning and then eventually when used multiple times, it doesn't seem to work.

When I probe and check the voltages, I get the following observations:

1. EN/UVLO: 4.9V
2. VCC: 5.2V
3. At the The High Side Buck MOSFET, the Gate Voltage is 1.5V. I believe its not getting fully ON and hence Voltage is not going ahead.

Custom Board 2: 

The circuit seems to work at the beginning and then eventually when used multiple times, it doesn't seem to work.

The circuit gives unstable behaviour where it starts to give 12V and desired Current but eventually the voltage drops to 3.2-3.5V and the current consumption increases to the maximum value set at the input supply.


I am attaching the schematic down below. We request you to kindly help us with the same. this plays a pivotal role in the circuitry. Thank You.

 

Kind Regards. 



  • 0
    TI__Mastermind 27760 points

    Hi Saira,

    1. How many pcs of the total boards have you seen the abnormal operation?

    2. Could you show the waveforms of SW1, SW2, Vout and iL when you saw it abnormal operating?

    3. Please also share the layout file with us to check.

    4. What is the input voltage range and max output current?

    5. What is the part number of the output capacitors?

    BRs,

    Bryce

  • 0 in reply to Bryce Xun
    Prodigy 170 points

    1. Hi I have made 5 PCBs and out of which all of them are showing abnormal Operation
    2. The 4 photos are as in the following order:
    SW1



    SW2


    Vout




    IL pin



    3. I'd like to request you to please let me send you mail with the Layout file. I won't be able to attach the file here on the forum due to IP reasons.
    4. Input Voltage Range: 9-12.6V in actual use case since we are suppling the voltage from a Battery. However, currently at the time of we are giving power directly at the input of the IC, providing 12V. Max Output Current is 1.5 to 2A. However, currently at the time of testing the load is only drawing 50mA.
    5. Since the 10uF/35V capacitor was unavailable, we have used 4.7uF/25V and part number is most likely GRM188R6YA475KE15D. The 220uF/35V is most likely EEE-1VA221UP.

  • 0 in reply to Saira Shaikh
    TI__Mastermind 27760 points

    Hi Saira,

    1. Can you show the waveforms at the moment of the output voltage falls from 12V to 3.2V?

    2. Have you checked if the impedance of the each pins are normal as OK board or not?

    3. Please send the friendship to me, so you can share the Layout file with me via message.

    4. I don't find the ESR value of the EEE-1VA221UP, can you tell me the value?

    BRs,

    Bryce

  • 0 in reply to Bryce Xun
    TI__Mastermind 27760 points

    Hi Saira,

    I have received the layout file, and the layout looks not good for SW2 trace, VCC trace, PGND-AGND connection, ISP-ISN connection, see layout guideline for more information.

    www.ti.com/lit/an/slvaer0b/slvaer0b.pdf

    But to locate the root cause for this phenomenon, the waveforms at the moment of abnormal is significant to us.  

    BRs,

    Bryce

  • 0 in reply to Bryce Xun
    Prodigy 170 points

    Hi Bryce,

    Thank you for the prompt response.

    1. Waveforms during abnormality

    2. The impedance at each pin show OPEN except PIn 7(4.1E) & Pin 13 (38K)

    4. I'll get back to you with the ESR value since its unavailable in the datasheet
    .WAVEFORMS B3 IRREGULAR VOLTAGE DROP TPS55.pdf

  • 0 in reply to Saira Shaikh
    TI__Genius 14950 points

    Hi Saira,

    We will wait for your feedback about the ESR value. Can you help check if the MOSFETs are damaged or not? Will the circuit return to normal when changing to new MOSFETs?

    Regards,

    Mulin

  • 0 in reply to Mulin Yuan
    Prodigy 170 points

    1.1Ohm @ 120Hz is an approximate value of ESR.
    MOSFET Don't seem to be damaged However, we tested on a New board with new MOSFETS and we have observed a similar pattern on all boards.

    We have tested 4 boards and each of them have the following observation.

    1. Initially it works fine for a few mins, as long as external supply is given.
    2. When we switch OFF and Switch ON the external Supply, the output seems to have gone. Additionally there is a voltage drop at the power supply and the Current goes into CC (Constant Current at the maximum set limit.)
    3. When the IC or Q3 mosfet is pressed, it seems to function normally sometimes. Not always.
    4. Can you please point out what are the exact issues with the layout, since we cross verified and none of it seems to be a direct problem causing issue.
    5. Can you please guide us what can be done, since it's a critical power source for our board. 

  • 0 in reply to Saira Shaikh
    TI__Genius 14950 points

    Hi Saira,

    Bryce is OoO, I don't have the layout file. Waveforms that you provide is tested when the device already work abnormally. Can you share the waveforms when device work normally? Since you find when power supply is on and off and then device damage, can you capture the input voltage waveform to see if there is any abnormal behavior? Can you check if there is any solder problem?

    Regards,

    Mulin

  • 0 in reply to Mulin Yuan
    Prodigy 170 points

    Hi Mulin,

    Can I share the layout file with you? Please accept my friendship request. 

    The waveforms in the document "WAVEFORMS B3 IRREGULAR VOLTAGE DROP TPS55" is the one when the irregular behaviour is observed. The Expected output voltage is 12V but I am getting only 2.38V as you can see in the waveform. 

    I'd like to request you to elaborate on the Device Damage point. I couldn't interpret properly.

    We have resoldered the whole Circuit properly. The issue seems to go away for a bit but the drop is observed again.

    Kind Regards.

  • 0 in reply to Saira Shaikh
    TI__Genius 14950 points

    Hi Saira,

    Since you can observe the drop again, can you capture the moment when damage occurs?

    Regards,

    Mulin