• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 4 answers
  • Subscribers 62 subscribers
  • Views 573 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.

TPS54260: Issue with 1.2VOUT @ 1.5A load

Jia Zhi Lim
Prodigy 150 points
Part Number: TPS54260

Dear all, 

I am doing a project with the requirement configuration stated below.

Configuration
Label Value
VIN 15V
VOUT 1.2V
OUTPUT CURRENT

1.5A

I use TINA simulation tool to determine the components value. Based on that, I had made some changes to the components value that is label in the schematic below with the reference from webench power designer. Then I am using TPS54260EVM-597 evaluation module (HPA597) 

However, when testing the circuit, I encounter critical issue listed below:

1: Input of Cboot voltage is 7.2V and the Output of Cboot voltage is 1.12V

2: Results for switching frequency measured before the inductor is not working

Please assist where the root cause is, Your prompt reply is appreciated.

  • 0
    TI__Mastermind 27045 points

    Hi Lim,

    PH node average voltage is close to Vout, voltage cross Cboot you measured is about 6V, this is correct in normal operation.

    What's output capacitor you used for 1.2Vout? did you apply some load current on output during testing?

    B R

    Andy

  • 0 in reply to Andy Chen
    Prodigy 150 points

    Hi Andy, 

    Thank you for your reply. 

    we use Aluminum cap 1000uF + on board 47uF + 47uF.

    we tested with/without load and the results (waveform) are the same. The only differences is with 1.5A load, there is a buzzing sound coming from the inductor. Without load there is no sound coming from the inductor.

    Jia zhi 

  • 0 in reply to Jia Zhi Lim
    TI__Mastermind 27045 points

    Hi Jia Zhi,

    Can you simulate circuit loop response in TINA? TPS54260 COMP network should be modified with output capacitor combination.

    I suggest you to remove 1000uF E-cap first, check if switching is stable at 1.2Vout, then add 1000uF Cout and modify the COMP network per data sheet instruction, or simulate it in Webench by editing the capacitance and ESR of output cap.

    B R

    Andy

  • 0 in reply to Andy Chen
    Prodigy 150 points

    Hi Andy,

    We have tried again on new evaluation modules. The values are replaced to be as shown below.

    The only difference is that we are using 2 x e-cap(470uF, 16V, unknown ESR) as Cout.

    I have attached pictures showing switching waveform and output voltage in without load and with 1A load.

    At no load condition, the switching seems not working properly, but the output voltage is stable.

    At 1A load condition, the switching frequency is not regular, and the output voltage ripple is too big, our design requires a lower ripple.

    Switching voltage measured before inductor without load

    Output Ripple without load (steady 1.2V with Vpp = 7.00mV)

    Switching voltage measured before inductor with 1A load

    Output Ripple with 1A load (1.2 V with Vpp of 166.00 mV)

    Do you have any suggestion on how should we move forward in solving the issue?

    Thank you.

  • 0 in reply to Jia Zhi Lim
    TI__Mastermind 27045 points

    Hi Lim,

    The SW waveform shows the loop is not stable.

    The Webench recommend to use capacitor with ESR <10mohm. you may try to use super ceramic cap 470uF 3.3V with this circuit.

    another solution is to use 1pcs 470uF 10V normal electrolytic cap plus one 10uF 6.3V ceramic cap on output, then modify the COMP network as below:

    Rcomp=22K

    Ccomp=15nF

    Ccomp2=1.8nF

  • 0 in reply to Andy Chen
    Prodigy 150 points

    Hi Andy,

    Thank you for the clarification, we tried simulation on the circuit with high ESR Cout(100mOhm) and the result show unstable switching as well.

    We have ordered cap with low ESR to test again, will update here after we tried with the low ESR cap.

    For your second proposed solution, we cannot use E-cap due to requirements constraints. But may I know what is the reason of the proposed change?

    Regards

    Jia Zhi.

  • 0 in reply to Jia Zhi Lim
    TI__Mastermind 27045 points

    Hi Jia Zhi,

    The E-cap is just recommended as alternative solution in case you don't have low ESR cap on hand.  

    B R
    Andy

  • 0 in reply to Andy Chen
    Prodigy 150 points

    Hi Andy,

    We have tried with using Cout with low ESR, about 2.5mOhm and the switching frequency is close to the simulation and the output voltage is stable at 1.2V with about 14mV Vpp. The design is fine.

    Thank you very much for pointing out the issue with ISR.

    Regards, Jia Zhi.