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.

LM26420-Q1: short-circuit to ground

Part Number: LM26420-Q1
Other Parts Discussed in Thread: LM26420,

dear

My circuit using LM26420-Q1, designed a way to output 3.3 V, the input is 5v, often there are veneer LM26420 SW pin resistance 4Ω or so (still work, only LM26420 extremely hot) or to the ground short-circuit situation. After the replacement of LM26420 phenomenon disappeared, the chip can work properly, SW impedance is normal. In normal operation, the current of 3.3 V is about 0.5 A.

Other output also used LM26420, output 2.5V 1.8V 1.2V 0.85V, etc. , but these voltage LM26420 controller did not appear a problem, so please help to see where my circuit design problem?

details sch and PCB shows as attachement, any advise? thanks in advance

  • Hi Raymond,

    Thanks for contacting us.

    From your description, it seems that the SW mosfets get damaged in certain conditions.

    Can you please provide the following info?

    - What is the maximum input voltage? How is it regulated?

    - What is the inductor value? I don't see it in the schematic.

    - What is the percentage of device where you see this problem?

    - When this problem happens, is only an output rail affected?

    - Have you noticed if this problem happens at the first turn on (possible damage during assembly), or after a while that the device is running (possible damage during operation)? 

    - What is the maximum voltage on the SW node? Please send an oscilloscope screenshot of SW waveform.

    Thanks,

    Stefano

  • dear

    What is the maximum input voltage? How is it regulated?
    HE:  max voltage=5.05V,normal use=5V
    - What is the inductor value? I don't see it in the schematic.
    HE:inductance bournsSRP2512A-1R0M
    - What is the percentage of device where you see this problem?
    HE: 35 devices,now 7 have problem,Occurrence probability  20%
    - When this problem happens, is only an output rail affected?
    HE:single 3.3V output channel short circuit,also have 2.5V and 3.3V output channel short in the same time。
    - Have you noticed if this problem happens at the first turn on (possible damage during assembly), or after a while that the device is running (possible damage during operation)?
    HE:According to the user's feedback, most of the power was found to have problems
    - What is the maximum voltage on the SW node? Please send an oscilloscope screenshot of SW waveform.
    HE:
  • Hi Raymond,

    Thanks for the data.

    I'll provide my feedback tomorrow.

    Thanks,

    Stefano

  • HI Raymond,

    Since this is getting a pretty long discussion, let's move it offline.

    I will write you an email.
    Thanks,
    Stefano