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LM25085A: LM25085ASDX/NOPB doesnt have any output.

Fatih Eksi
Prodigy 10 points
Part Number: LM25085A

Tool/software:

Hi,

I wanted to use this part for CC-CV converting. I used same schematic config as in datasheet (my schematic below) but IC seems not to be active. As if it is in shutdown mode. When I measure gate pin of PFET with osciloscobe I only see a flat high voltage. It is not trying to drive the fet. What can be the problem? What am I missing? I tried various changes but no result. Thanks in advance.

  • 0
    TI__Mastermind 24115 points

    Hi,

    It looks like the C13 capacitor is not in the application schematic example. Please remove this capacitor and see if that helps.

    Can you please also note which schematic you are referring to in the datasheet. It looks like your component selection is somewhat different from the figure 28 example circuit.

    Additionally please ensure that the current limit on your power supply is set appropriately.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 10 points

    Hi Joshua, thanks for answer. 

    I resoldered the board to be sure if some solder problems are there or not, new things came up.

    Now IC is trying to drive the mosfet but mosfet is not acting. 

    My mosfet is : IRF5803TRPBF. EVM board has SI7465DP-T1-E3.

    VCC and VIN difference is about 8VDC. And it is stable.

    So it tries to drive the mosfet with this difference of VIN and VCC. But I think it is not fast enough to turn on with the 140ns pulse of IC as you can see osciloscob pic below. I decided to order the mosfet that is used in EVM. Can this be the problem? 

  • 0 in reply to Fatih Eksi
    TI__Mastermind 24115 points

    Hi Faith,

    Yes, an improper MOSFET can result in issues with the part's in-operation. Please check the PFET section of the device datasheet for more information on these requirements.

    I am also seeing that the EVAL board uses a Vishay Si7465DP P-MOSFET. The one you listed is an N-Channel. Can you please provide a link to the EVAL board you are referencing?

    Did you also remove the C13 capacitor as previously mentioned?

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    TI__Mastermind 24115 points

    Hi Faith,

    As I have not heard from you in some time, I will close this thread for now.

    Please feel free to reopen the thread if you have any additional questions.

    Thank you,

    Joshua Austria