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Original question:

LM25011: Doesn't work properly

LM25011: Battery charger not working

Felipe Marques
Prodigy 230 points
Part Number: LM25011

Hello everyone,

I have developed a battery charger based on LM25011, but, I am not able to make it work. Even tough I have read the datasheet and the support forum, no idea came up, so, I appreciate any toughts.

The initial project was: Vin = 32V, Vout, 20.7V and Iout = 2A.

Below you can find the schematic.

In the beginning, the output voltage was just as equal as the input voltage, but, after some tests some IC burned. I noticed the IC was hot (maybe the temperature protection was working in order to protect it). So, I have tried to change some components, as C8 = 4.7uF, C11 = 10nF, R16 = 100kohms, R19 = 1kohms, R20 = 4.64kohms, L1 = 10uH and C13 = 10uF, in order to make anything works. After that, I decided to look at the layout.

I tried to minimize the input loop adding new conductor bettween C10 and C11 ground pads. It did not help. Tha same for the output loop, when I added a wire betweem R17 ground pad and the track close to the LM25011 thermal pad.

Thank you in advance!

  • 0
    TI__Expert 3835 points

    Hi Felipe,

    How is the device not working. Can you show me some start up waveforms and switch node?

    Do you have top layer GND pour for your device? It could be heating up because of poor thermal dissipation from the layout.

    Your input capacitors are too far from the device. Put this as close to the device as possible. Move R16 farther and reduce the component size. Your power good resistor is not pulled up to any voltage. Remove if the feature is not needed. Your switch node is very large. Move the inductor close the device. Do a single trace to C12 to minimize the boot trace. Your FB trace is very long, move R20 and 19 closer to the device.

    I suggest you follow the layout guidelines on section 10.1 of the datasheet.

    Regards,

    Ethan

  • 0 in reply to Ethan T
    Prodigy 230 points

    Hello Ethan,

    Thank you for the reply.

    About yuor questions and suggestion:

    "How is the device not working. Can you show me some start up waveforms and switch node?"

    i don't have any components to make this tyest. Yesteday I ordered new samples. As soon as they arrive I make this measurement.

    "Your input capacitors are too far from the device. Put this as close to the device as possible."

    OK!

    "Move R16 farther and reduce the component size."

    OK!

    "Your power good resistor is not pulled up to any voltage. Remove if the feature is not needed."

    OK, I will remove it.
    "Your switch node is very large. Move the inductor close the device."

    OK!

    "Do a single trace to C12 to minimize the boot trace."

    Do you mean remove the plane and add traces instead?

    "Your FB trace is very long, move R20 and 19 closer to the device."

    OK!

    As I mentioned before, I need new samples in order to make such tests. It is very likely I have them until next Friday.

    Tahnk you again Ethan.

    Regards,

    Felipe.

  • 0 in reply to Felipe Marques
    TI__Expert 3835 points

    Hi Felipe,

    I look forward to your update. Yes remove the boot strap plane and add a short thick trace to the capacitor.

    Regards,

    Ethan