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TPS25940: TPS25940L

angelo valente
Prodigy 10 points
Part Number: TPS25940


Tool/software:

Hi team,

I'm working with the TPS25940L. The input voltage is an 8V battery, with an OV=9.9V and a UV=5.5V. The eFuse works well, even with undervoltage and/or overvoltage. 

In the connection chain, after the eFuse, I have two other switching devices (one buck for 3V3 and the other buck-boost for 5V). Everythig works fine until I apply a load (such a WI-FI); in fact, the voltage drops at the eFuse output.

The peak current measured on the IMON pin is about 1.5A, and the eFuse has been set with a current limit of 5A.

The problem is detected whether a load is connected to +3V3 or +5V. If I bypass the eFuse, everything works normally even with the load connected.

I don't know why the eFuse behaves this way.

Do you have any suggestions? 

I've attached an image showing the connection (figure 1 ), the waveforms captured by the oscilloscope (figure 2) and the circuitry of eFuse (figure 3)

Figure 1Figure1

Figure 2Figure 2

Figure 3Figure 3



  • 0
    TI__Mastermind 39295 points

    Hi Angelo,

    Please share the waveform labels also without them, it is very difficult to make sense of it.

    angelo valente said:
    The problem is detected whether a load is connected to +3V3 or +5V. If I bypass the eFuse, everything works normally even with the load connected.

    From this it looks like the input supply of eFuse should be able to handle the load and should not have foldback but for sanity check, probe Vin of eFuse and see if the supply is dropping when you face this above-mentioned issue.

    angelo valente said:
    The peak current measured on the IMON pin is about 1.5A, and the eFuse has been set with a current limit of 5A.

    Another thing is your schematic doesn't have many caps near the device. If we add any sudden load, the current will come from the input of eFuse and may cause OCP event. Check the FLTb signal. It doesn't go low for OCP event.

    My colleague will take over from here.

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    Prodigy 10 points

    Hi Arush,

    I checked the eFuse input voltage, and the power supply (battery) does not decrease when the above-mentioned problem occurs.

    Unfortunately, I didn't include the current measurement.

    I also added additional capacitors (64uF) to the output eFsue, but the problem persist. 

    I attach an image showing the waveform of the FAULT and PG signals, when the problem occurs.

    Thanks for the support.

    Best regards 

    Angelo

  • 0 in reply to angelo valente
    Prodigy 10 points

    Hi team,

    I did another test. I connected a resistive load to the eFuse's output and discovered that it isn't actually limited to 5A (despite the 17.6K resistor at ILIM pin17), but it's already limiting me at 1A. 

    Is it likely that component has some issues related to the manufacturing process?

    Another question that I wanted to ask is how the component behaves when the board it's mounted on, overheats (about 70°C) and whether this could affect its characteristics and/or perfomance?

    Thanks for the support.

    Best regards 

    Angelo

  • 0 in reply to angelo valente
    TI__Expert 5670 points

    Hi angelo 

    Thank you for your patience

    I would like you to send me current waveform measuring at the output rather than from IMON pin. Because we need accurate information on current to understand the behaviour

    Can you share me whole schematic and also can you please ground the DEVSLEEP pin and perform the test. It looks like the device is entering into DEVsleep mode. So can you do that test and send waveforms with VIN VOUT IOUT PG pin in it 

    Best Regards

    Sailendra

  • 0 in reply to Sailendra Kumar
    Prodigy 10 points

    Hi Sailendra,

    unfortunately, I can't ground the DEVSLEEP pin.

    I also connected an electronic load to the eFuse output, increasing the current to 4A (in 100mA steps), but at about 1A, the eFuse output voltage began drop (to about 4V), while the input voltage remained steady at 8V.

    I tried another identical board with the eFuse mounted on it and it worked perfectly.

    Thanks for the support.

    Best regards 

    Angelo

  • 0 in reply to angelo valente
    TI__Expert 5670 points

    Hi angelo 

    Could you please tell me why you cannot ground DEVSLEEP pin?

    Can I also know how you are loading the device. Have you used CC load or CR load?

    Best Regards 

    Sai

  • 0 in reply to Sailendra Kumar
    Prodigy 10 points

    Hi Sailendra,

    Unfortunately on my board where the eFuse is mounted, I don't have a TP on the DEVSLEEP pin, so it's difficult for me to solder a wire and connect it to ground.

    For the load, I first used a CR and the a CC load. But in both cases, at almost 1A of load, the eFuse output voltage dropped.

    Best regards 

    Angelo

  • 0 in reply to angelo valente
    TI__Expert 5670 points

    Hi angelo

    Can you let me know at least  if the DEVSLEEP is grounded internally by checking voltage on it.

    Also  would like you to send me current waveform measuring at the output rather than from IMON pin. Because we need accurate information on current to understand the behavior

    Best Regards

    Sailendra

  • 0 in reply to Sailendra Kumar
    Prodigy 10 points

    Hi Sailendra,

    unfortunately, I no longer have the board.

    However, the eFuse output current was costant, while the output voltage decreased after (about) 1A.

    We repleaced the eFuse (only the eFuse, without modifying the circuitry)

     and it work fine. There were no further problems. 

    In fact, I managed to get up to 4.5A of load.

    Best regards 

    Angelo

  • 0 in reply to angelo valente
    TI__Expert 5670 points

    Hi Angelo

    Thanks for the update

    Best Regards 

    Sailendra