• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 386 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS61022: Device Repeatedly Fails; even at low load currents; (SW Pin is shorted to GND); Vin=3.6 to 4V, VOUT=5.5V

Jerry Molnar
Prodigy 210 points
Part Number: TPS61022

Hi!
We are unable to successfully use the TPS61022 - it always fails in our board.....and it is a bit of head-scratcher!!

The failure mode is that the SW pin is shorted to GND.

The part is configured for a 5.5V output and a single Li-Ion battery input (The part fails whether we use a battery or power supply as the input).

The schematic is as follows:

It might be a bit hard to see the values - the caps are 22uF, 10V, 0603 X7R ceramics.

The upper resistor R7 is 820K, 1%; The lower resistor is 100K 1%

There are (not shown) 2X 100uF, 16V aluminum polymer caps (24mOhm ESR) on VIN as well. (Digikey P16468CT-ND).

We tried 2 different inductors. Both are from the datasheet - The Wurth 744316100 and the Coilcraft XAL7030-102MEC. Same result.

We didn't try a feed-forward cap on that board (I did on the eval board (5V) but it didn't seem to matter);

The circuit has to supply a maximum of 2.25A at 5.5V.

It has never failed at no load.

It always fails if we try to put the full load.

I had it supplying 100mA and then 200mA, seemingly fine (Using a pure resistor load and no other load).
Then a power on/off/on cycle...and the part was blown up. I can't recall if the 200mA load was connected during this cycle, but most likely it was.

U2 is the device
C41, C42 are the electrolytics
L3 is the inductor
C24 is the input ceramic
C28, C29, C30 are the output ceramics.


Any insights.... clues.... suggestions? Schematic, layout???

Thanks in advance!

Jerry Molnar

  • 0
    TI__Genius 12335 points

    Hi Jerry,

    Looks like there are some problems with your layout, the output capacitors should be placed close to VOUT and GND as much as possible, otherwise the large parasitic inductance would cause large voltage spike on the SW node, and then damage the IC.

    You can refer to this app note for more details about the layout guidelines.

    https://www.ti.com/lit/an/slvaes4/slvaes4.pdf?ts=1697076086366&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS61022

    And more, about your schematic, I find you used 3x22uF, 0603 capacitors. We recommend to use 3x22uF, 0805 capacitors, because the effective capacitance of ceramic capacitors is related to the package size. The effective capacitance of 0603 capacitors is usually only half of the capacitance of 0805 capacitors. This may be not related to the issue you met, but may have a risk of instability.

    Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 210 points

    Hi Nathan,

    Thanks for your reply - very helpful and much appreciated.

    We will improve the layout on the next rev...

    I have 3 minor follow-ups:

    - In the eval board schematic, there is a 49.9 ohm resistor. Is that a placeholder in case it is needed in combination with a feed forward capacitor?...i.e. what is the purpose of the 49.9?

    - When do you recommend a feed forward capacitor. It is mentioned in passing in a couple of places, but no clear guideline.

    For example, if we put 4X22uF caps on the output, does that potentially increase the need for the feed forward capacitor?

    - Finally, since our design uses the part at the max output voltage 5.5V, does that imply any risks to damaging the part?

    Thanks!
    Jerry

  • 0 in reply to Jerry Molnar
    TI__Genius 12335 points

    Hi Jerry,

    About the three questions,

    1.the 49.9ohm resistor is used to test the bode plot, if you don't need to test the bode plot, then you don't need to place the resistor in you board.

    2.About the feed-forward capacitors, please refer to the datasheet, please be noted that the 40uF here is the effective capacitance not nominal capacitance. For 4x22uF, 0603 ceramic capacitors, you don't need to add the feed forward capacitors.

    3.No risk, 5.5V is within the safe operation range.

    Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 210 points

    Hi Nathan,


    Thanks for your thorough and complete answers to my questions. Much appreciated.

    All the best!
    Jerry