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TPS61200-EVM Issues/Help!!!

Adam Cooke
Prodigy 110 points

Hi. I am using the TPS61200EVM. I am using four .5V/400mA solar cells in series as the input. However, when I test the output with a voltmeter, I am getting nothing. What am I doing wrong..? Am I missing something?

Any help would be much appreciated. I am a high school student.

 

Thanks

  • 0
    TI__Guru**** 150830 points

    Verify with the voltmeter and oscilloscope that your input voltage is stable and above 0.5V.  Make sure you connect the supplied jumper across pins 1 and 2 of JP1 (VBAT and EN) to enable the chip.  Remove any load that is connected to the output to begin with.  This should get you up and running.

  • 0 in reply to Chris Glaser
    Prodigy 110 points

    Thanks for the response. When I have a 3V lab supply as the input, I only get 3.3V out (I should be getting more?). However, if I use the solar cells at 1.5V as the input, I am getting nothing out, 0V.... The chip is enabled and the voltage us stable. I thought this was designed to work with solar cells?

  • 0 in reply to Adam Cooke
    TI__Guru**** 150830 points

    Yes, the IC works with solar cells.  The EVM as shipped outputs 3.3V.  This can be changed by changing the FB divider resistors.

    Do you have a load connected?  If so, remove it from the output.

    Can you post an oscilloscope picture of Vin, L, and Vout at both 5 us/div and 1 ms/div?

  • 0 in reply to Chris Glaser
    Prodigy 110 points

    Finally figured out the solar cells as input and it works great. However, I need 5V out. How exactly do I change the FB divider resistors?

     

    Thanks

  • 0 in reply to Adam Cooke
    TI__Guru**** 150830 points

    Glad you got it working.  Can you post what was wrong and how you solved it so that all may learn?

    Please read the datasheet and user's guide which are located here: http://focus.ti.com/docs/toolsw/folders/print/tps61200evm-179.html  They may have also shipped with the EVM.   There is an equation for adjusting the feedback resistors in the datasheet.

  • 0 in reply to Chris Glaser
    Prodigy 110 points

    All I did to fix it was I took the solar cell outside, and it worked fine. When four were hooked up in series indoors, I was getting 1.3V from the solar cells but when attached to the boost converter, I was getting 0 out. I figured that maybe there wasnt enough current or something from the indoor lights, so I decided to give it a shot outside and bingo. All is well as far as that goes.

    I read about programming the output voltage in the data sheet by adjusting the feedback resistors. However, I am not sure how to physically do it...?

  • 0 in reply to Adam Cooke
    TI__Guru**** 150830 points

    Yes, the solar cells probably did not have enough energy to support the start-up of the converter.  When the converter would turn on, it would crash the input bus at which point it would turn back off.  This would only be observable on a scope, not a multimeter.

    So the datasheet has the equation for calculating the resistors on page 15.  I assume that you found that.  Then, the schematic in the user's guide shows what value resistors are on the board.  You just need to change one resistor to change Vout.  I suggest that you change the top one.  To physically do it requires the desoldering of the resistor and then the soldering of the new one in its place.