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TPS63002: Output fluctuation or Disabled?

Willies Wu
Prodigy 100 points
Part Number: TPS63002

I followed the recommended design for all of the components on datasheet and try to use this Vout to drive multiple high power LEDs with a N-channel MOSFET before connecting the the cathode to the GND.

Will this configuration turn off the chip ?

 The vout I got were always 0.1V or 0.2V.

  • 0
    TI__Expert 5425 points
    The way you connected the TPS63002 looks ok to me. I do not find a specification or a part number for the LED in you schematic. In many LED's the heatsink is either connected to the anode or the cathode of the LED. In your circuit this would mean that either the LED or the MOSFET is shorted. Depending on the type of the short and the resistor values this can cause an overload condition during startup of the TPS63002 which means the output voltage will not rise.
  • 0 in reply to Juergen
    Prodigy 100 points

    Thanks Juergen,

    The LEDs I selected are LZ1-00G102-0000.

    Its thermal pad is electrically neutral, so I connected them to the GND.

    The current limiting resistance is 536 ohm, so each path shall use around 2.6 mA.

     Will the chip have an issue, while the current draw is very small ?

    Or 

    Will the chip have an issue, while the Vout is open circuit?

    Thanks

     

  • 0 in reply to Willies Wu
    TI__Expert 5425 points
    So the LED's should not be a problem.
    The TPS63002 does not have a problem operating at light load or no load at the output. To debug your circuit I actually would recommend to disconnect all the LED 's and check whether you get the nominal 5V output voltage.
  • 0 in reply to Juergen
    Prodigy 100 points

    Thanks Juergen,

    I have tested disconnecting all LEDs, but the Vout was still ~0.2 V.

    Besides, I also tested a new inductor and a new IC, but all of them gave me the same Vout.

    Is there any way to measure whether the IC's  heat pad contact the PCB successfully?

    I saw someone posted about heating pad issue, hence we had already been cautious to assemble it. 

  • 0 in reply to Willies Wu
    TI__Expert 5425 points
    I think if you want to check the soldering of the exposed thermal pad when the device is soldered on the board you need X-ray inspection. If you take it off you may get an indication whether it was soldered when you find solder on the exposed thermal pad of the device and the corresponding pad on the PCB.

    Another option why you are not getting any output voltage is soldering problems. If pins are shorted e.g. to the exposed thermal pad or to adjacent pins, or if they are not connected the device may not work properly as well.
  • 0 in reply to Juergen
    Prodigy 100 points

    Thanks Juergen,

    I am still testing the chip. 

    Do you think the layout will affect the result?

    (I think it will affect the transient response, but it should not affect whether we will get 5 V or not)

    I also tried to follow the recommendation on the datasheet for the layout.

    Thanks 

  • 0 in reply to Juergen
    Prodigy 100 points
    Hi Juergen,

    I tested today again, and some how the R3 had a large voltage drop (~2.5 V), which really confused me, as this would disable the chip.
    But why would this happen ?
    I have checked the resistance value, which is 100 ohm as the datasheet used.
    '
  • 0 in reply to Willies Wu
    TI__Expert 8420 points
    Hi

    Were you able to solve the issue? did you find out any bad soldering?

    Thanks,
    Sabrina
  • 0 in reply to Sabrina
    Prodigy 100 points

    Hi Sabrina,

    After the testing, the new boards did work,

    but it's not simple to debug the soldering with the heating pad or slight shift of the pins,

    so sometimes we needed to use a new IC, which meant the yield rate probably won't be good in a large scale.

    If there is any testing method that can be easier to utilize,

    it will be really helpful.

    I think from the the schematic perspective, it does what it needs to do.

     

  • 0 in reply to Willies Wu
    TI__Expert 8420 points
    Hi,

    Yes debugging the soldering could be tricky, optical verification is not very effective.
    If the ICs are assembled during PCB manufacturing, the manufacture may have methods to check it.
  • 0 in reply to Sabrina
    Prodigy 100 points

    Thanks for the follow up.