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LM5122 output issue

peng ben
Prodigy 20 points
Other Parts Discussed in Thread: LM5122, LM5122EVM-2PH, LM5069

Hi ,

     I use LM5122 design DC-DC for battery charger device,24Vto 60V@2A,  the device output for R Load can work 60V @1.8A, but connect to 48V battery, battery voloatge is 51V, the device can't work, out put just 0Ato 0.18A wave,output voloatge is battery voloatge 51V. for some minute,the LM5122 chip broken. out feeback Rfbt use 110K,Rfbb use 2.2K. also CSN,SCP use 100&100pf.

     SCH use WEBENCH .

  • 0
    TI__Guru 58761 points

    Hi

    The cycle-by-cycle current limit of LM5122 is triggered if the output voltage is lower than the target output voltage for a long time.

    This cycle-by-cycle current limiting activates LM5122's internal hiccup mode operation eventually. To disable the hiccup operation, please tie RES pin to ground.

    Regards,

     

  • 0 in reply to EricLee
    Prodigy 20 points

    Dear Eric Lee,

            Thnks for reply me, I do it by your suggestion, the devis out put is OK.  the DC-DC efficency about 98%.

    thanks again & HAPPY X’MAS!

  • 0 in reply to EricLee
    Prodigy 50 points

    Hello Eric Lee

    I have the same problem as a previous post regarding the use of the LM5122 in a battery charger application. I am working with the LM5122EVM-2PH evaluation board with 28V output connected to a battery bank. When I use a resistive load, the output voltage is stable at 28V up to several amps but if I connect the output to a 24V battery bank (28V charge voltage), the voltage immediately drops to the same voltage as the battery (about 25V) with an output current under 80mA. I can then hear a "buzz" from the circuit.

    Why is this and how can I overcome it ?

    Regards

  • 0 in reply to Steven Lambert
    TI__Guru 58761 points

    Hi

    - Connect RES pin to GND

    - Check your input power supply current limit.

    - Check if UVLO pin voltage drops below 1.2V.

    - Check if the initial battery voltage is higher than input voltage. 

    Regards,

  • 0 in reply to EricLee
    Prodigy 50 points

    Hi Eric Lee

    Thanks for your support. I have tried your suggestions but unfortunatelly they have had no effect.  The UVLO voltage stays stable at 1.8V.

    I have noticed that if the input supply voltage is increased above the output voltage and then reduced again, the circuit functions as expected and the output voltage regulates. This seems to trigger or reset something.

    Could this have something to do with the Skip Cycle Mode or Pulse Skipping ?

    Kind regards

  • 0 in reply to Steven Lambert
    TI__Guru 58761 points

    Hi 

    Did you see an improvement ? 

    I don't think there is something to do with the Skip Cycle Mode or Pulse Skipping. 

    Regards

  • 0 in reply to EricLee
    Prodigy 50 points

    Good Day Eric Lee

    I found the problem to be inrush current which triggered the over-current protection of the LM5122. I have since added an inrush limiting circuit using the LM5069. It works much better now and I am able to achieve the 430W I was aiming for.

    Many thanks for your support.

    Regards