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LMZM23601: Inductance reducing issue

Kazuki Kuramochi
Genius 10965 points
Part Number: LMZM23601


Hello Expert,

My customer facing the issue that mounted inductor's inductance is reduced after mounting.
Then, I have some questions for this device as below.

1. Is there any limitation from the point of view of damage for inductor?
2. Is there any limitation on the Vin range(Max 36V) when when we use this device with Vout=3.3~12V condition?
3. Could you tell me the operating temp range of mounted inductor?(125C or 85C or others?)
4. Does this device  has any rating regarding pressure and bending?(we worried about any damage happened during manufacturing procedure by physical damage.)
5. In the datasheet's functional diagram, there isn't any description regarding parasitic diode on LS and HS FET. We this there is parasitic diode on FET. Dose this understanding correct?


I'm looking forward to hearing back from you.


Best regards,
Kazuki Kuramochi

  • 0
    TI__Mastermind 19911 points

    Hello, 

    Here are some comments.

    1. Assuming the proper soldering profile is followed, there should be no damage to the inductor during the mounting process. 

    2. The maximum input operating voltage is 36V. 

    3. 125C

    4. Not aware of such rating. Normally the pick and place force is minimal in SMD mounting. 

    5. Yes, there are body diodes, just like any synchronous switcher. 

    Cheers, 
    Denislav

  • 0 in reply to Denislav Petkov
    TI__Genius 10965 points

    Hello Denislav,

    Thank you for your swift reply.
    It is really helpful for me.

    I understand your explanation however I have new questions.
    Would you answer following questions?

    1. Is there any limitation regarding physical damage from the bending mounted board and etc...?
    2. Have you heard similar issue that device cause abnormally  heating up and output failure with decreasing of inductor's inductance after few days from the mounting?
    3. Datasheet has vin derating curve when we use with Vout<=2.4V case, Is there there similar chart from 2.4V to 3,3V?

    I'm looking forward to hearing back from you.


    Best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Mastermind 19911 points

    Hello Kuramochi-san, 

    Here are some comments. 

    1. We have gone through normal BLR qualification for this device, just like any other device. If there is some excessive bending in the application board, I imagine there could be damage. 

    2. Not after few days of mounting. Usually if there is some issue with mounting the part due to pick-and-place or solder profile, it will be apparent right away. Do you have any waveforms of VIN, VOUT, and the SW node (SW can be probed on the inductor) showing the part operation. It could make sense to submit the part for failure analysis it is has failed.

    3. The VIN derating for <2.4V is due to the minimum on time of the part. High VIN to low VOUT results in small duty cycle and low on-time. The curve puts a limit on maximum VIN so the minimum on time is not violated. For higher output voltages the minimum on time will not be reached even at maximum input voltage. 

    Regards, 

    Denislav

  • 0 in reply to Denislav Petkov
    TI__Genius 10965 points

    Hello Denislav-san,

    I appreciate your swift support.
    Would you confirm my comments as below?

    1. Would you provide explanation material of BLR thermal cycle and mechanical shock purification for us?
    2. Is there possibility to happen damage on inductor during mounting process?
      1. They have confirmed that this issue improved when they replace inductor from normal unit to defective unit.
      2. So we suspect this issue is from damaged inductor.
    3. I understand that there isn't any derating chart between Vin=2.4 ~ 3.3V but it is only related with min on time.

    For the measurement result, I'll share you when I receive it.


    Best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Genius 10965 points

    Hello Denislav-san,

    Sorry for rushing you but this issue happened on customer's Pre-MP stage and it cause schedule delay of MP.
    Would you provide answer soon?

     
    Best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Mastermind 19911 points

    Hello Kuramochi-san, 

    I am waiting for feedback from the team on the BLR specifications. 

    Apologies for the delay, hoping to provide additional comments tomorrow. 

    Regards, 

    Denislav

  • 0 in reply to Denislav Petkov
    TI__Genius 10965 points

    Denislav-san,

    Thank you for sharing your situation.
    I understand and waiting your update.


    Thank you and best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Genius 10965 points

    Denislav-san,

    I have question for this device's behavior when input voltage is larger than 28V.
    Datasheet said that switching frequency is smoothly reduced from 1000 kHz if Vin is larger than 28V.
    They want to know about whether there is any risk when they use this device around Vin=28V condition.
    Would you tell me your opinion for this case?

    Our customer worry about the device happen oscillation if Vin repeat enter and exit this condition.

    Also, I'm waiting your updated regarding other remained questions.


    Best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Mastermind 19911 points

    Hello Kuramochi-san, 

    I received feedback from the team. 

    1. The package BLR testing followed JEDEC JESD22-A-104F Test condition G -40/125C, 60 min per cycle.

    2. Yes, the frequency will gradually fold back as the input voltage goes above 28V. If they have input transients around 28V they may see frequency fluctuation around the VIN change and some change in output ripple voltage. I would suggest testing the input transient in their application and monitor the output voltage to see if the ripple or frequency reduction is acceptable for the application. 

    Regards, 
    Denislav

  • 0 in reply to Denislav Petkov
    TI__Genius 10965 points

    Hello Denislav-san,

    Thank you for your support.
    I understand that  VIn=28V is boundary condition that it cause frequency variation and it may cause ripple and noise.
    As far as my understanding, it may cause issue regarding noise but there isn't any risk for stability. Is this correct?

    For the test, I understand it was tested with JESD22-A-104F.
    However, this test is temperature cycle test.
    We would like to know about whether there is any rating regarding Vibration, shock and any mechanical damage test as like as JESD22-B111,  JESD22-B113?


    Best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Mastermind 19911 points

    Hello Kuramuchi-san, 

    Correct, operating the device at 28V is not a reliability risk. 

    I will check with the team on the vibration/shock question.

    Cheers, 
    Denislav

  • 0 in reply to Denislav Petkov
    TI__Genius 10965 points

    Hello Denislav-san,

    I'd like to share about detailed information.
    So I sent mail to you.


    Best regards,
    Kazuki Kuramochi