• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 161 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMR33630: LMR33630 not providing the right voltage

Daniele Cavazza
Prodigy 20 points
Part Number: LMR33630

I'm testing a prototype with related to this schematic using LMR33630ADDA:

Since in the layout the connection to AGND was missing I removed the IC and added a wire to ensure this connection ad soldered again the IC.

With Vin=12V, I get 2V inthe output instead of 5V.

IC sinks 120mA even with no load connected to the output and this is strange.

Assuming that everything was soldered properly, what could be the reason of this behaviour?

Thank you

  • 0
    TI__Prodigy 490 points

    Hi Daniele,

    That's strange. Were you having the same issues prior to adding the AGND connection? 

    Could you also provide us with your board layout?

    Regards,
    Carol

  • 0 in reply to Carol Zhang
    Prodigy 20 points

    Hi Carol,

    before connecting the board Vout of LMR33630 was 0V and current from power supply 10mA (leds and other LDOs).

    After connecting AGND PAD Vout of LMR33630 is 2V and current from power supply is 120mA 

    Here some layout screenshots:

    TOP

    INNER1_GND

    Thank you for your support

    Daniele

    INNER2_VCC

    BOTTOM

  • 0 in reply to Daniele Cavazza
    TI__Prodigy 490 points

    Hi Daniele,

    Thank you! Your layout looks reasonable. 

    Are you able to replicate this issue with a different IC? It is possible that the original device got damaged when it was originally powered up without the AGND connection. 

    Regards,
    Carol

  • 0 in reply to Carol Zhang
    Prodigy 20 points

    Hi, 

    I tried with many boards, al least 3 and the result was always the same.

    With the last board I paid attention not to power up the board before doing the wiring modifications.

    So the problem seems to be not random but systematic.

    There could be something wrong around the board, but if I try to supply the +5V net and the +12V net separatly I don't see any short circuit or anomalous current sinking from the power supply.

    What else can I check?

    Thank you

    Daniele

  • 0 in reply to Daniele Cavazza
    TI__Prodigy 490 points

    Hi Daniele, 

    Could you confirm that your boot capacitor is the correct value and soldered on properly? If there is an issue with the capacitor, there may not be enough energy to drive the power MOSFETs, causing Vout to be lower than expected. 

    In the process, it would also be helpful to just confirm that all values are expected and soldered well. 

    If there are no issues here, could you provide us with waveforms of Vin, Vout, and SW?

    Regards,
    Carol

  • 0 in reply to Carol Zhang
    Prodigy 20 points

    Hi Carol,

    your suggestion to check CBoot was very useful.

    I taked out Cboot from the board and measured it with a multimeter: it was 0nF. After that I mounted a new 100 nF capacitor and the switching was providing 5V as apected.

    These steps was repetead with other 2 boards with the same result.

    So the issue was the value of CBoot and 0nF isvery strange, I have to check this issue with the manufacturer.

    Thank you very much for your help.


    Reghards,

    Daniele

  • 0 in reply to Daniele Cavazza
    TI__Prodigy 490 points

    Hi Daniele,

    No worries at all! I am glad we were able to figure out your issue. 

    Let us know if you have any other questions.

    Regards,
    Carol