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0V on FB pin for TPS60500

Pontus Olvebrink
Prodigy 70 points
Other Parts Discussed in Thread: TPS60500

Hi

I'm having some problem with the TPS60500 on my final design for a project I'm doing. I have a supply voltage of roughly 4.9V which

I want to convert to approx. 3.3V and I've set the voltage divider correctly. But for some reason I get an output voltage of 4.39V and 0V

at the FB pin for some reason. I'm using the reference design for the project and all values except the voltage divider has been changed.

The whole solution should work because I've verified it once with a test board which gave me exactly the right voltages (3.27V on Vout and

0.8V on FB) but for some reason it's not working for my larger design. Is there a possibility that the chip got destroyed when soldering it even

though it looks fine. Or is there some way to find out what has gone wrong?

 

Hope someone can help me

 

Best regards

Pontus

  • 0
    TI__Mastermind 36110 points

    I'm interested in knowing what your project is about.  The TPS60500 is very easy to design and work with, so the most likely cause of your problem is a soldering issue that is shorting pins together or not properly connecting a pin to the PWB.  You could have damaged the IC during manual soldering if you heated the IC too much. You could also have ESD damage if you are not working in an ESD safe environment.  You should measure the voltage waveforms on the flying capacitors to see if the IC is switching.  Also, I don't understand what you mean when you say the output voltage is 4.39V and 0V.  It should be a fixed output voltage and should not be switching.  Can you show scope pictures of the waveforms.

  • 0 in reply to Matthew Day
    Prodigy 70 points

    Hi and thanks for the reply!

    I'm using it in a low powered sensor platform that's going to be powered by an old iPAQ using serial communication to to talk to a MSP430. I'm sorry if I confused

    you there about the voltages. It's not switching on the ouput voltage, it's a constant 4.39V. But when measuring the node at the FB pin it's 0V even though it

    should be 0.8V. I've verified  that all of the pins are correctly soldered and pretty sure that I didn't overheat it as well. As for ESD damage that might be a possibility

    as I've only done it at a normal labb in my school with no fancy equipment except for a really good soldering iron. I will see if I can use one of the oscilloscopes

    to see if there is some switching on the flying capacitors and see if I can get some pictures for you. If I see no switching is it safe to assume that the IC is broken

    for some reason and just remove it and replace with a new one?

     

    Best regards

    Pontus

  • 0 in reply to Pontus Olvebrink
    TI__Mastermind 36110 points

    It's most likely a damaged IC.  If you measure a short circuit between Vin and Vout, the IC is definitely damaged.

  • 0 in reply to Matthew Day
    Prodigy 70 points

    Hi Michael I found the error which was really stupid. I had gotten some soldering led beneath one of the resistors and

    accidentaly connecting it to the ground plane... That's the reason I couldn't figure out how it was linked to ground the whole

    time even though I went through it in a microscope a couple of times.

     

    Thanks anyway!

    Pontus