• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 599 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LMZ23608 short-circuited to GND for unknown reason

Maxime Puech
Prodigy 140 points
Other Parts Discussed in Thread: LMZ23608

Hi,

I'm using the LMZ23608 for a 24V / 5V conversion on a new design, and I am experiencing some issues. I powered on the board, and after a while the 24V power supply indicates an overcurrent (current limited to 1.13A). I disconnected the power supply and measured a resistance of about 2 ohms between the 5V supply rail and ground. I unsoldered the LMZ23608 and the short-circuit was not there anymore. The problem happenned in two boards already, and it seems to happen randomly. 

What are the reasons why the LMZ23608 would be short-circuited ? Overcurrent ? Overheating ? What about its overcurrent protection and thermal protection ? Today I don't know if the problem occurs because there is another problem on the LMZ23608 load, or if the problem is dued to the LMZ23608 itlself. 

In normal operation, the cunsumption on the 5V rail is 800mA, and the case temperature of the LMZ23608 is about 60°C, nothing that seems to exceed its spectication. 

Thank you for your help.

  • 0
    TI__Genius 10115 points

    Hi Maxime,

    About how long does it take after the power up of the LMZ23608 before the current increases to the current limit?

    Is it immediate on turn on or does it take time?

    In terms of what would cause the output to be short circuited, this kind of damage is usually from overvoltage or from overheating when the LMZ is mounted on the PCB.

    If the short is not caused by damage internal to the module, here are a few possibilities.

    1) A short on FB pin  to Agnd will cause the output voltage to go up and draw more current.

    2) A short of SH can cause the current to be uncontrolled. 

    I am attaching the guideline for surface mounting the part so that you can review it.

     

    Regards,

    Marc4670.Texas_Instruments_English_LMZ1_LMZ2_PowerModules_SMT-Design_Guide-SNAA214_REV_H_Lock.pdf

  • 0 in reply to Marc Davis-Marsh
    Prodigy 140 points

    Hi,

    I have had this problem with 2 boards, and we were using them for days before the short circuit occured. 

    I don't think we had any overvoltage problem since we are using a reliable AC/DC power supply for the board. I suspect overheating, but as I said the case temperature was only 60°C in nominal operation. 

    The FB and SH pin are not short-circuited to ground, and the circuit behind the LMZ23608 works fine after the short-circuited LMZ23608 was replaced.

    I spoke to a coworker who told be that he had some problems with the LMZ23608 too : the component wasn't working at all, it was like if the circuit was open. He replaced it with a new LMZ23608 and it was working fine. Is this possible that we have defective components ? 

    What about ESD ? Can it cause a short-circuit of the output ?

    Thanks for your help,

    Regards,

    Maxime.

  • 0 in reply to Maxime Puech
    TI__Genius 10115 points

    Please check your solder reflow process and see if it complies with the document I posted.  If the reflow temperatures are exceeded you could see an internal short that is intermittent.

     

    Marc