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LM3478: Not able to operate it for high current application (O/P: 4.2V 8A)

Dhvanish Parekh67
Prodigy 205 points
Part Number: LM3478

Hi,

We are using LM3478 in one of our project with below configurations:

Vin: 3.0V to 4.1V

Vout: 4.2V

Iout: 8A

Below is the schematic that is designed based on the suggestions provided on webench:

Same has been taken from the webench design tool.

Few observations as below:

1. As soon as output current crosses 3.5A input capacitor C161 starts heating (>50-60 C)

2.  If raising load current >4A IC stops the switching and we receives VIN-0.3V in output.

3. Tried changing resistor value for R163 and change the operating frequency but no any change observed in results.

Thanks,

Dhvanish Parekh

  • 0
    TI__Guru 68495 points

    Hi Dhvanish,

    Thank you for designing with the LM3478.  Please use a quality ceramic capacitor for C161.  Also, please use short cable to connect your power source and remember to twist the input and return cable.

    Changing R163 is not a solution here.  Anyway, you have an error in your schematic.  C133 should be placed across ISEN pin and AGND. Change it to 1nF.

    Best Regards,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 205 points

    HI Youhao,

    Thank you for the response!

    We tried modifying the capacitor as suggested and also applied few other changes as listed below:

    1. Changed input capacitor C161 to 47uF (previously 15uF).
    2. Changed C133 to 1nF and kept it across ISNS and GND pin (tried with / without 100R (R157) between Rsns (R170) and Isns pin.
    3. Added 47uF Electro. capacitor on the output side.
    4. Shorted input path for switcher IC.

    As a result was able to get the output of 4.2V upto 3.8A output current. As soon as we try to increase the current above this, the switcher IC stops working.

    Any other area to look into? Or different experiment advise to perform?

    Thanks,

    Dhvanish Parekh

  • 0 in reply to Dhvanish Parekh67
    TI__Guru 68495 points

    Hi Dhvanish,

    Sorry for the delay owing to my business trip.  Could you monitor the ISEN pin voltage waveform?  Please how both overview (a few cycles) and a zoomed in (one or two cycles). 

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    TI__Guru 68495 points

    Hope the issue has been resolved, given no further update from your side.  You are welcome to re-open this thread by adding a new post.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 205 points

    Hi Youhao,

    We were able to achieve upto 4A successfully with the same design without any modification.

    Now we are trying to reach up to 9A (originally design for) and at the same time checking the efficiency and the other parameters also.

    If possible give me your mail id so that I can be in touch with you till I complete overall experiments. 

    Once again, Thank you for the extended help!

    Thanks,

    Dhvanish Parekh

  • 0 in reply to Dhvanish Parekh67
    TI__Guru 68495 points

    Hi Dhavanish,

    I am really glad to hear your progress!  I am send you a connect request through PMS, lets continue the discussion through emails.  Let me close this thread here.

    Best Regards,

    Youhao