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LM3414HV: Schematic review

Kai Hsiao
Guru 12675 points
Part Number: LM3414HV
Other Parts Discussed in Thread: LM3414

Hi Sir 

Please help to review schematic 

Vin=8~50V ,Iout=1A ,Vout=6V

Please 

  • 0
    TI__Mastermind 28655 points

    Hello Kai,

    Everything looks okay except when your input voltage is on the high range, 50V.  The minimum on-time:

    "7.3.2 Minimum Switch ON-time
    As the LM3414 features a 400 ns minimum ON time, it is essential to make sure the ON time of the internal
    switch is not shorter than 400 ns when setting the LED driving current. If the switching ON time is shorter than
    400 ns, the accuracy of the LED current may not maintain and exceed the rated current of the LEDs. The ratio of
    the LED forward voltage to input voltage is restricted by the following restriction, as shown in Equation 1."

    At 500 KHz minimum on-time will be around 300 ns with 6V output and 50V input.

    Also, TVS1, SMAJ70CA, will not protect the LM3414, the clamping voltage is much too high.  The '70' is the standoff voltage, not clamping voltage.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    TI__Mastermind 28655 points

    Hello Kai,

    I haven’t heard back from you, I’m assuming you were able to resolve your issue.
    If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 20 points

    Hi Sir 

    Please help to review PCB Layout

    Vin=8~50V ,Iout=1A ,Vout=6V

    Please 

  • 0 in reply to Roger Liao1
    TI__Mastermind 28655 points

    Hello Kai,

    Can you tell me what the layers are?  I see vias (I'm not sure what the vias are doing, just heatsink?), a red layer and a transparent red layer.  If the red traces are carrying current they are small for 1A.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 20 points

    Dear Irwin:

    How r u!

    I Reply is as follows,

    1. PCB 2 layers

    2. T/H is on and down 2 layers

    3. A red layer and a transparent red layer are Polygons

    Best regards,

    Roger

  • 0 in reply to Roger Liao1
    TI__Mastermind 28655 points

    Hello,

    It's not real clear in the picture if that is a ground plane on the bottom and what it covers.  I would added some vias next to the (-) side of CIN to make the GND path shorter, CIN is the source for the high frequency switching current.  Other than that is should work beside the points I made about Vin, Vout and switching frequency plus TVS1 above.

    Best Regards,