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SN6507: Fsw Problem

İskender önem
Prodigy 10 points
Part Number: SN6507

Hi team,

I have a problem about adjusting switching frequency "Fsw" of SN6505. It is known that it operates between 100kHz to 2Mhz. However, when I placed a 111k Ohm resistor between CLK pin to GND. Driver does not work.

I have tried with 30k, 40k and 50k Ohm resistors for between CLK to GND pins. Results are same: Driver doesn't work.

When I shorted CLK to GND or placed 9.6k Ohm resistor, it works properly at 1.07 Mhz as it mentioned in datasheet.

I want to adjust Fsw to 105 kHz. Is there anyone who can help me?

Regards,

  • 0
    TI__Mastermind 49535 points

    Hi Iskender,

    Welcome to TI E2E forum!

    Could you please check if there was any connection issue on the PCB? You might also want to test it another PCB with a different sample just to make sure there wasn't any issue and whatever the problem with earlier PCB might not happen in a new PCB.

    We expect the switching frequency to align according to the resistor used at RCLK as per the Table 8-1 in SN6507 datasheet and these have been tested by us and other customers. Hence, I request you to check if there is any problem with the PCB or any connections. Please do check and let me know if you still see an issue, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points

    Dear Koteshwar,

    Thanks for your answer.

    I have rebuilded circuit but it still doesn't work. 

    If there is a connection error for CLK pin, it will stop switching.

     

    Clearly we can understand that CLK is connected properly. Other check point is that I have tried 9.6K resistor for CLK. Again it is operates at 1.07Mhz.

    To sum up, I can say that there is no connection error.

    However, IC stop switching when I connected other resistor (30k 40k and 111k) to CLK. I know you are approved your products after test but there is an issue. 

    Note: I have tried 4 different SN6507 and all of them work at 1.07MHz for shorted to GND or 9.6k to GND.

  • 0 in reply to İskender önem
    TI__Mastermind 49535 points

    Hi Iskender,

    Thanks for confirming that you have verified it is not a connection and for sharing additional inputs.

    İskender önem said:
    Note: I have tried 4 different SN6507 and all of them work at 1.07MHz for shorted to GND or 9.6k to GND.

    Did you mean to say you have tested 4 different SN6507 devices and all of them work at 1.07MHz when RCLK is 0Ω or 9.6kΩ but do not work when connected to 111kΩ? If this is true, then it is possible the issue isn't necessarily with the device but maybe with other component in the design. Could you please share your schematic so that I can check if there is anything that could be causing an issue?

    For the power supply to work at 111kHz, the transformer needs to be designed accordingly. If it is a 1MHz transformer with low V-t product then the design might not work as expected although I would still expect to see switching waveform at the SW1 and SW2, even if they are not very clean. Please do share the schematic along with the transformer part number so that I can review the same. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Mastermind 49535 points

    Hi Iskender,

    I wanted to reach out and check if you still facing the switching frequency issue. If you do, please do help share the information requested in my previous post. Thanks.


    Regards,
    Koteshwar Rao