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TPS25910: TPS25910 power limit

user132886
Prodigy 80 points
Part Number: TPS25910

Dear Sirs!

I have a 14,5VDC power supply, I put the TSP25910 in series with it. I have some small load on the TPS25910's output and there is a big one: 14,5V/2,2A. I set the current limit to 3,5A

Unfortunately this load made the chip to be hot - 125°C

I don't really understand the datasheet and the EVM document: I thought that the IC could have 3-20VDC output at 5A as I see in the EVM's documents schematic on page 3.

In contrast with this in the datasheet I see that there is a Power limit 3-7.5W  on page 4. and there is a Power limit vs Junction temperature Figure 3. on page 8. and there is a Maximum load at startup on page 17. (it means to me that 12W could power up...)

So what is the truth? Did I misunderstand the power handle capacity of this chip? Could I use it for my 14.5VDC/2.2A load or not?

Please help me!

Regards: Zsolt

  • 0
    TI__Guru 57737 points

    Hi Zsolt,

    TPS25910 has Power limiting functionality but it is not Output power limit. It limits the POwer limit across the Internal FET. You can see this in the block diagram below,

    The Internal FET experiences high power loss across it during startup and short circuit conditions. These are the conditions where there is voltage across the FET and current flowing through it. During steady state conditions, the power loss is only due to (I*I*R) loss which is much less than 5W.

    Now regarding the chip becoming hot,

    • How did you measure the temperature?
    • What is the Ambient temperature?
    • Where are you testing this device ? Is it being tested on the EVM? This is to understand RQJA of the device.
    • What is the kind of load that you are using ? Is it a resistive load or an electronic load?
    • What is the total load current ? I understand that you have two loads at the Output of TPS25910.
    • Do you see a drop in Output Voltage ? This will let us know if the device is current limitimg.

  • 0 in reply to Praveen GD
    Prodigy 80 points
    Dear Praveen!

    Thanks for your answer, yes meanwhile I realized how tthis chip works... but it is too late for our project.

    I desoldered my GATE capacitor and it seems to be good, but after an hour measurements I have to say that this chip is not good for our project, I saw that at starting up the chip's power limiting was working without GATE capacitor.

    How did you measure the temperature?
    with IR thermometer

    What is the Ambient temperature?
    23°C room temperature

    Where are you testing this device ? Is it being tested on the EVM? This is to understand RQJA of the device.
    No, it is our hardware

    What is the kind of load that you are using ? Is it a resistive load or an electronic load?
    It is a tablet

    What is the total load current ? I understand that you have two loads at the Output of TPS25910.
    I have max. 2.5A load on 14.5VDC

    Do you see a drop in Output Voltage ? This will let us know if the device is current limitimg.
    No, there is no voltage drop.

    Is there any pin compatible eFuse device which I could use instead of TPS25910?

    Thank you.
  • 0 in reply to user132886
    Prodigy 80 points

    Some clarification:

    I have to charge a tablet's battery and I have some electronics which need 5 and 3.3VDC from the 14.5V input voltage, so I have 2 more DC/DC converter on the board.

  • 0 in reply to user132886
    TI__Guru 57737 points
    Hi Zsolt,

    We do not expect the IC temperature to go as high as 125C with 2.5A Load and 25C Ambient. Can you replace the IC and perform the same test?
    Also, please share you schematics.
  • 0 in reply to Praveen GD
    Prodigy 80 points

    Dear Praveen!

    This high temperature situation come into being during startup, not in the steady state! Although sometimes the power up is going without problem - without high temperature state - and the my hardware is running good!
    I could show you my schematic only on next week.

    Zsolt

  • 0 in reply to user132886
    TI__Guru 57737 points
    Hi Zsolt,

    As there would be power loss during startup which will increase the Junction Temperature. Please test the IC at your maximum ambient temp condition with maximum load possible during start up and make sure that the device does not hit thermal shutdown during startup.
    If the device hits thermal shutdown at startup you will have to reduce your load during startup.
  • 0 in reply to Praveen GD
    Prodigy 80 points

    Hello!

    If there is thermal shutdown at room temperature, I don't really understand why I would have to try it at max. ambient temperature.

    Yes, I think we could not use this chip.

    Thank you,. Zsolt