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SN6507DGQEVM: SN6507DGQR IC part

Karthik B
Expert 1310 points
Part Number: SN6507DGQEVM
Other Parts Discussed in Thread: SN6507

Hi Team,

  • We are using SN6507DGQR this part in our design and used as per the recommendation in the datasheet to get the VOUT=24V using Vin=24V., but we see an issue in the output voltage,
  • We are observing 37V~38V at the output, could you please suggest how to debug this and fix this on board asap.
  • attached the schematics reference & review.

We are using the below Parts:

  • Transformer:750319697
  • Diode : PMEG200G20ELRX
  • Inductor : 74438335330

Ref Schematics:

Regards,

Karthik

  • 0
    TI__Guru 54125 points

    Hi Karthik,

    Thank you for reaching out.

    Can you please confirm if you are observing 37V to 38V under what load conditions?
    Can you please confirm if the inductor L10 is populated during the tests?

    If the L10 inductor is populated, then please remove the inductor and replace it with a short and test.
    If you are still seeing the issue then please share the SW1 and SW2 waveform. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Expert 1310 points

    Hi Koteshwar Rao,

    We are seeing 37V or 38V at NO LOAD condition we are using digital multimeter and oscilloscope to measure the voltage.

    Yes we confirm that above testing is with L10 inductor

    Now we removed the L10 Inductor as per your feedback and directly shorted the path and see the VOUT voltage to be 26.5V when measured using digital Multimeter & 27V when measured in Oscilloscope.

    We have attached the SW1 & SW2 waveforms for your reference in the attachment.

    SN6507DGQR_SW1_SW2_Waveforms.pdf

    Regards,

    Karthik

  • 0 in reply to Karthik B
    TI__Guru 54125 points

    Hi Karthik,

    Thank you for conducting the suggested test and confirming the output voltage. The inductor L10 is only needed when duty cycle control feature is used, otherwise it doesn't need to be used. Although the inductor might not affect the output voltage when load is applied, but under no-load conditions, it is possible for the inductor have an impact on output voltage.

    27V of output for your design seems expected, once load is added, I expect it to come down to voltage between 24V and 25V.

    I will go ahead and close this thread but if you have any further questions, you can respond back or create a new post. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Expert 1310 points

    Hi Koteshwar Rao, 

    Having 27V when we measure it without load is not reasonable correct, because this is a product and when we want to use this voltage there will be always a confusion if i can use a 24V device or not is there any way we can fine tune this and get it atleast to the 24.5V or 25V

    Do you see the necessity to mount the RDC resistor by any chance, currently its DNP on the board.

    This is a product that will be used by our end customer and if they check and see that there is 27V instead of 24V then the boards will not be accepted and we may get NC for the same.

    Regards,

    Karthik

  • 0 in reply to Karthik B
    TI__Guru 54125 points

    Hi Karthik,

    Thank you for clarifying your concerns.

    Please note that SN6507 is an open-loop push-pull transformer driver and the output it produces is unregulated output. Due to this, the output is not expected to be tightly regulated and if one needs such a regulation, they are required to use an LDO as a post-regulator to get a tightly regulated output.

    I am copying below a couple output voltage vs output current example plots from SN6507 datasheet to indicate the expected output voltage variation. The variation of output voltage shown below is about 0.5V for one plot and 1V for another but this is from 20% load to 100% load. At 0% load, the output voltage is expected to be considerably high. To get a regulated 24V output, please consider using an LDO at the output.

    To get a regulated 24V output, please consider using an LDO at the output.

    Karthik B said:
    Do you see the necessity to mount the RDC resistor by any chance, currently its DNP on the board.

    RDC is needed if duty control feature need to be used. This feature provides partial line regulation where the duty cycle is adjusted with the variation in input voltage. This is still open-loop and it cannot match the regulation that can be achieved by a closed-loop power supply solution.

    Let me know if this answers your question, thanks.


    Regards,
    Koteshwar Rao