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Original question:

TPS61088: Advice to solve a problem with TPS61088 and TPS62142.

WEBENCH® Tools/TPS61088: Issue with TPS61088: Doesn't function

Jacob Booth
Prodigy 40 points
Part Number: TPS61088

Tool/software: WEBENCH® Design Tools

Hey everybody,

I'm trying to boost a 4.2V lion 18650 battery to 12V at around 3A maximum discharge. I chose the TPS61088 but it is not working currently. Would you be able to help me debug my circuit? I made it using the TI Webench designer. I am concerned that my inductor selection is too high (4.7uH) and its saturation current is too low (~6.3 A I think) I thought that this would be sufficient because I would be drawing significantly less than that. I am also concerned that the values for my error compensation network are incorrect. Also, should I tie the enable pin to VIN or would VCC be better? I want the regulator to be always enabled. I don't believe soldering is an issue, but if there is an easy way to check that would be helpful. There is an LC filter and a ptc fuse on the output, but I don't think these would cause issues. So far testing has been done with no load except a status LED (and fuse and LC filter). 

Currently the circuit just passes through the battery voltage with about a 0.5V drop (4V in ~3.45V out) and I can't see any switching behaviour on the oscilloscope. I've attached an image of my schematic. Thanks so much for the help.

  • 0
    TI__Mastermind 40080 points

    Hi Booth,

    Your schematic is OK!  Are the maximum output 12V 3A?

  • 0 in reply to Helen chen
    Prodigy 40 points
    No, the regulator does not function. It doesn't do anything except pass the battery voltage through with about a ~0.5 V drop. So I put 4V in I get 3.5V out instead of 12V. It doesn't seem to be switching. I will try to replace it with a new part and solder at low temperature but I don't think its a soldering issue. I have two of the boards assembled and they both exhibit the same behaviour.
  • 0 in reply to Jacob Booth
    TI__Mastermind 40080 points

    Hi Booth,

    The schematic is OK. But I think there may exist some problem in the pcb board or the soldering. Could you please share the layout to me? If possible , you can apply for a TPS61088 EVM board from the local TI office.

    Too low solder temperature also can't solder well,  and u may depend on the soldering flux during the soldering.

    what is your maximum output power , is it 12V/3A?

  • 0 in reply to Helen chen
    Prodigy 40 points

    Here is the layout I used. I tried to match it to the datasheet recommendations. I soldered a new chip on and this one doesn't have any voltage on the output. It still doesn't do anything.

    The maximum power was meant to be designed for 3A at 12V, but right now I am getting nothing.

  • 0 in reply to Jacob Booth
    TI__Mastermind 40080 points

    Hi Sir,

    The layout doesn't has big problem. But it can't output 12V/3A. it can work well at no load condition. Did you check the no load condition?

    if it doesn't work at the no load condition, then please check the whether it is well soldered. There's an ESD diode parallel with each pin. for example, please check the diode between the GND and the EN pin (net), if there's a diode between GND and the EN net, then the EN pin is well soldered.

    Then you can use the same way to check Vcc pin, SS pin, COMP pin. for the Ilim pin, you can check the impedance from the Ilim net to the GND, it should be 100k ohm

    By the way, please check the layout example on datasheet page 20.

  • 0 in reply to Helen chen
    Prodigy 40 points
    Thank you for your help. Yes those are small mistakes because of how I setup the ground pours. I will fix those in future but they aren't causing the problem.

    You were correct, it was a soldering issue. There wasn't a short, I just wasn't using enough solder paste. I ordered a stainless steel stencil because I wanted to assemble two of these boards, and I applied solder paste by squeezing paste with a credit card. I probably did not apply enough pressure or I did not use the right kind of solder paste because not enough paste was dispensed. I quickly took off the chip and manually applied some flux and paste and then resoldered and it now works well. Deceiving because it looked like it was soldered correctly and there was no shorts.

    Thanks again.
  • 0 in reply to Jacob Booth
    TI__Mastermind 40080 points

    Great news! Good luck :)