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TPS5405: Diagnosing Damaged Regulator

Sara Stredulinsky
Prodigy 20 points
Part Number: TPS5405
Other Parts Discussed in Thread: TPS54202

Tool/software:

I develop a prototype PCB that included a TPS5405 to regulate voltage between an 11.1V LiPo battery and the rest of the system. I used the following set up for the regulator:

On my first test of the regulator, using a DC Power Supply set to 11.1V it output 5V perfectly as designed. Awhile later, I finally tested it on the actually battery, only for it to output almost no voltage. A possible culprit for the malfunction is an error I made in the design that resulted in an op-amp frying, as after I removed the op-amp from the PCB, the regulator started regulating voltage again, just not correctly. With an input of 6V from the power supply it output less than 5V (1), at around 8V it output 5V (2), and at around 11V it output 3V (3). When connected to the battery it output 2V (4).

(1)      (2) (3)

(4)

What I'd like to figure out is if the chip itself is damaged and needs to be replaced, or if it's an issue with the supporting RLC network.

I checked each of the pins on the scope while on battery power (I may have gotten some of these out of order):

BOOT:   VIN:  

ROSC: (may have mixed up with SS)   LX:

COMP:

What sort of output should be expected at each pin? Does it seem to be a chip problem or some other issue? What other tests should I run if necessary?

Thank you for your time!

Sara

  • 0
    TI__Mastermind 27636 points

    Hi 

    I will take a look at this and get back to you later.

    Thanks and best regards.

  • 0
    TI__Mastermind 27636 points

    Hi Sara

    The 1mH inductance is very large. Please also share the layout images.

    Please connect to the DC supplier and check the waveform of Vin, Vo ,LX, during power up and during steady state. 

    Also, what's you application ? we have newer part like TPS54202 that is synchronous, easy to use, and high efficiency. 

    Thanks and best regards.

  • 0 in reply to Gui He
    Prodigy 20 points

    Hello Gui He,

    Thank you for your help!

    I've reviewed the TPS5405 documentation and my notes, and I'm honestly not sure why I used the 1mH value for the inductor. I must have lost track of the actual value somewhere along the way. What inductor value would you recommend?

    Here is the top and bottom layout of my PCB (the bottom is mostly ground plane):

    The application is a prototype PCB for my senior design project as an Electronic Engineering Technology student. It's a control board for a small hovercraft, based around an Arduino Nano as the microcontroller, where the battery directly feeds a fan motor while the buck regulator steps down the 11.1V to a steady 5V for the rest of the board. Unfortunately, I don't have time to design and order a revised board at this point, so I'd only be able to swap the TPS5405 to a chip with the same package and pin-out.

    I didn't have any easy way to add all the oscilloscope images individually, so I put them in a Google Drive folder. Each is labelled with the pin, the condition (startup or steady), and whether or not it was AC or DC coupled.

    https://drive.google.com/drive/folders/1D8Q7R_tvZUb4qyt5twe2QwmMPsSrxkRq?usp=drive_link

    I also tried varying the voltage and noted the following behavior: if I started at 8V and slowly ramped up, the output voltage stayed steady at ~5.2V up to 11V, but at 12 V the output got wobblier and dropped to 4.24V and lower at higher levels. However, if I went to a higher voltage, then backed down again to 11V the output voltage remained lower than 5V.

    Putting the 11.1V battery on (which seems to have an effective voltage closer to 11.4-11.7V), the output voltage stays at ~1.2V.

  • 0 in reply to Sara Stredulinsky
    TI__Mastermind 27636 points

    Hi Sara

    please let me check and get back to you later.

    Thanks and best regards.

  • 0 in reply to Sara Stredulinsky
    TI__Mastermind 27636 points

    Hi Sara

    Thank you for sharing the information and sorry for late reply. I moved to new department and got busy. I suggest you measure the Vin and see if there is any overshoot during power up. Especially if there is a long cable input from the battery to the buck Vin. 

    The layout also need optimization, the Cin should be placed as close as possible to the Vin and GND pin of the device to eliminate voltage spikes on SW. 

    Please connect VSENSE to the C10 _Vout terminal instead of the L1_Vout terminal.

    Seems I have no access to the files. Not sure if the IC on you PCB is damaged or not, recommend you replace a new device and do the test and check Vin and SW voltage waveform during power up.

    Please note that the Cin should use capacitor with voltage rate >Vinmax. The inductor: please check the current spec of the L1, the Isat should > the peak current limit of TPS5405.

    You can take a look at the TPS5405EVM User Guide.

    Thanks and best regards.