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LM25122-Q1: LM25122-Q1 ISSUE & Schematic review

CHO SR
Genius 3185 points
Part Number: LM25122-Q1

There was a problem using LM25122-Q1.

Input : typ 12V
output : 24V, 2A

However, the customer has a shutdown in output load 1.8A.

Could you review my schematic as attached file.

Schematic review.pdf

  • 0
    TI__Guru 59435 points

    Hello CHO,

    I cannot observe anything obviously wrong in the schematic. Could you please share your inductor specifiction and please measure the inductor current shortly before the system turns off.

  • 0 in reply to Brigitte
    Genius 3185 points

    Hi Brigitte

    Sorry for the late reply.

    The customer checked late because he was on vacation.

    1.Attached is the inductor specification. 

    2. The inductor current measurement is not confirmed.

    However, the customer tested the inductor change, and the problem was not solved..

    Inductor Part : EMA13050S-330M --> EMA13050S-100M 

    EMA13050S Series-Datasheet.pdf

  • 0 in reply to CHO SR
    TI__Guru 59435 points

    Hello CHO,

    Changing the inductor from 33uF to 10uF will not really help to increase the current, as this increases the ripple current by a factor of 3.

    What is the minimum and maximum input voltage? Could you please ask the customer to check the input voltage on the input capacitor at 1.8A output current?

  • 0 in reply to Brigitte
    TI__Guru 59435 points

    Hello CHO,

    The current rating of the inductor seems not to be sufficient for the application. Please exchange the inductor with at least 11A current rating and check the maximum output current again. (this is only for testing)

  • 0 in reply to Brigitte
    Genius 3185 points

    Hi Brigitte

    1. What is the minimum and maximum input voltage?
    • Min : 10.6V
    • Typ : 14.4V
    • Max : 20V
    1. Could you please ask the customer to check the input voltage on the input capacitor at 1.8A output current?
    • Input cap : 330uF(AL)*2ea, 10uF(ceramic) * 2ea, 0.1uF(ceramic) * 2ea, 0.01uF(ceramic) *2ea
    1. Please exchange the inductor with at least 11A current rating and check the maximum output current again. (this is only for testing)
    • 33uH(rated 6.8A) and 10uH(rated 12.5A) are same the symptom.
    • But 10uH generate heat.
  • 0 in reply to CHO SR
    TI__Guru 59435 points

    Hello CHO,

    Please test with a 33uH inductor with 11A current rating not a 10uH with 12.5A rating.

    Please measure the voltage on the input pin while the output current is at the maximum achievable.

  • 0 in reply to Brigitte
    Genius 3185 points

    Hi Brigitte

    Please test with a 33uH inductor with 11A current rating not a 10uH with 12.5A rating.

    --> To be updated after purchase of inductor. ( ~ Aug 21 )

    Please measure the voltage on the input pin while the output current is at the maximum achievable.

    LM25122-Q1_Data.zip

    1. LM25122 Loadless EN pin input and output waveform.

    2. Start after connecting load.(1.9A)

    3. Shutdown after load connection. (1.95A)

    4. After the shutdown.

    5. No-load CSP & CSN

    6. CSP & CSN After Load Connection

    7. CSP & CSN during shutdown

    8. Update the schematic to a pdf file.

  • 0 in reply to CHO SR
    TI__Guru 59435 points

    Hello CHO,

    Please reduce the R1003 and R1005 to 10 mOhm and check the maximum output current again.

  • 0 in reply to Brigitte
    TI__Guru 59435 points

    Hello CHO,

    As I did not hear back from you, I expect that you have been able to solve your issue and will now close the thread. If this is not the case, please post below or create a new thread if this one is already locked.