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Startup Problem with TPS71701DCK

Gerald Bobe
Prodigy 50 points
Other Parts Discussed in Thread: TMS320C28345

I'm using a TPS71701 in a 2.5V Supply.

The device is configured for 2.5V as described in the Datasheet, and the load current ist very low. I'm using a 10µF X5R Capacitor at the input and at the output. The input Voltage is 3.3V and the enble pin is connected to Vin.

Actually I have the following behavior:

At an Ambient Temperature of 30°C or less everything works fin, and the temperature of the device never goes higher than 65°C. But if I schwicht of the device after a certain time of operation, everything is roughly warmed up 50°C, then the starup of the device fails, and the output remains at 0V. If the temperature goes down to 20°C, the cycling of the supply is followed by normal operation. I can reconform the chip behavior also, if I warm up the unconnected device to 50°C, in thaat case I won't stat either.

I have this behavier in 10 out of thousand units, and the problem moves with the TPS71701 to an other unit.

Has anyone a tip  for me?

Thanks,

Gerald

  • 0
    TI__Mastermind 41770 points

    Hi Gerald,

    Do you have any other components on the input or output of the LDO other than the input/output caps and the load?

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    Prodigy 50 points

    Hi Darwin,

    here is the answer for Your questions:

    At the Output there are a 2 additional 100nF Caps for decoupling. The output powers only the VCCAnalog Supply of an Altera Cyclone III (3C5) Device.

    The Input is Sourced from a 3.3V Digital System Power Supply with a lot of decoupling Capacitors and digital devices like the FPGA I/O, a TMS320C28345 I/O and a bunch of LVC Logic devices. Ist absolutely stable with a clean power up behavior, rated 2A in total.

    I investigated some more things Today:

    If I replace the TPS with a new one, the supply works fine on the same PCB.

    More interesting is, that the non functional TPS works fine in the 1.8V PLL analog supply of the TMS320C28345.

    Thanks for Your help in advance,

    Gerald

  • 0 in reply to Gerald Bobe
    TI__Mastermind 41770 points

    Hi Gerald,

    Since the failures don't transfer when replacing IC it probably is not the board. It may be that the devices are damaged. Do all failed units use the same TPS top marking code?

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    Prodigy 50 points

    Hi Darwin,

    the top marking of all our devices is "BMT". Including the functional and non functional units.

    I have done some further measurements to evaluate that behavior:

    1. I put a 10R for current Measuerement in the output, that did not change the behavior, works at low temp, fails at ca. 60°C.

    2. I removed all load exept the 10µF and the voltage divider, that did not change the behavior, works at low temp, fails at ca. 60°C.

    3. I put a resistive load with 40mA in, that did not change the behavior, works at low temp, fails at ca. 60°C.

    Attached you will find two plots, the first is the startup in normal operation, the second is with the LDO pr heated to 60°C. With input voltage, output voltage and current.

    Hopefully You have an idea,

    Gerald

  • 0 in reply to Gerald Bobe
    TI__Mastermind 41770 points

    Hi Gerald,

    I am unable to view the waveforms you have attached. In any case, it seems from the description above the devices might be damaged. You will need to contact your local TI FAE to get working samples and begin the failure analysis process for the failed units.

    Regards,

    Darwin