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TPS62913: Technical issues

Zhonghui Xu
Expert 5445 points
Part Number: TPS62913

Hi team,

I got a question from customer.I put it in the word

.The output ripple of tps62913 is large.docx

Thank you very much for your help.

Best regards,

  • 0
    TI__Mastermind 49370 points

    Hi Zhonghui,

    I will check this and get you back tomorrow.

    Thanks,

    Nancy

  • 0
    TI__Expert 7860 points

    Hi Zhonghui,

    The schematics provided in the word document are in agreement with the typical application. 

    A question I would like to ask the customer is if they have been able to measure output voltage ripples smaller than 8mV on other circuits when using their oscilloscope test setup? This could help verify that they have the correct equipment setup for measuring small ripple voltages and that noise or limited resolution from the ADC isn't causing the 8mV peak they are describing. 

    It would also be helpful if a plot of Vout vs. time, was supplied when Iout is at rated load.

    Nancy may also be able to provide more feedback.

    Thanks,

    Joseph

  • 0 in reply to Joseph Conrad
    TI__Mastermind 49370 points

    Hi Zhonghui,

    I agree with Joseph's input. Besides his comments, Here are my suggestions.

    The schematic and layout look good to me. The ripple waveform in your document shows picking up some noise during measurement. Please refer to TPS62913EVM user's guide for output ripple measurement recommendation.

    1.  We don't recommend to use a normal 10x oscilloscope probe with a high-impedance termination to the oscilloscope. 

    2. Please use a 1x probe, so you can get a higher resolution waveform on the scope.

    3. Zoom in the waveform with different time scale(like 400ns/div or 1us/div). So we can see few cycles with clarity.

    4. The EVM user's guide recommend to use a coax cable with 50ohm termination to measure the ripple. If you could not do that. You may measure the ripple on the EVM with your set up and compare to the ones in the EVM user's guide. This will rule out the setup and measurement issue.

    5.As EVM user's guide recommended, please check your inductor and Ferrite bead placement orientation. For  low noise  orientation, the "dot" or "mark" needs to be placed on SW side.

    6. Make sure the LB1 Ferrite bead is recommended.

    Thanks,

    Nancy

  • 0 in reply to Nancy Zhang
    TI__Expert 5445 points

    Hi,

    Thank you for your help.

    it is useful.

    Best regards,

  • 0 in reply to Nancy Zhang
    TI__Expert 5445 points

    Hi zhang,

    Thank you for your time.

    The customer have one more problem .please check  the word.

    TPS62913 reply.docx

    Thanks,

    Best regards,

  • 0 in reply to Zhonghui Xu
    TI__Expert 4645 points

    Looking at the information provided, the schematic shows that the spread spectrum feature is enabled by using the 42.2k resistor for S-CONF.  Can you try the circuit an 18.2k resistor for S-CONF and see if the behavior is different? 

  • 0 in reply to Steve Schnier
    TI__Expert 5445 points

    Hi team,

    The customer has replaced the resistance. Please check the attachment.

    TPS62913 reply_0701.docx

    Thanks a lot.

    Best regards,

  • 0 in reply to Zhonghui Xu
    TI__Expert 4645 points

    There seems to be a step change at the same frequency as the converter, approximately 2.2MHz. What coupling could be happening on the board to cause this.  Can the SW node be shown as well? The VOUT signal also looks very noisy.  I believe the measurement is from a barrel-tip measurement across an output cap, correct?  This may be picking up noise, but since I have not seen this on any board yet, If the same measurement technique is used on a TPS62913 EVM, does the output look good?  If not, it is the measurement technique. Have the same components been put on an EVM to see if there is an issue there?  If there is no issue with the same components on an EVM, then the cause is likely layout.  If it can be seen on the EVM, it may be components. 

  • 0 in reply to Zhonghui Xu
    TI__Mastermind 30031 points

    Hi , 

    Sorry that  I will close this threat first. Please re-open it if there is any future question.

    BRs,

    Lucia