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tps61202 unstability

seybyer
Prodigy 40 points
Other Parts Discussed in Thread: TPS61202, TPS61200, TPS61070, TPS61220

been using a tps61202 for a sloar charger. tps61202 is included in the first module that converts the input from the solar panel (max of 6V) to 5V. its output will be then forwarded to the next module that charges a lithium ion battery.

i have used the schematic on page 1 of  tps6120x datasheet (lower part). As I have observed, there were no much difference bet the one i used and the one shown in the evaluation kit. I know that it was not the same circuit that is shown in the evaluation kit but there were instances that the circuit worked. but now, its not functioning. should i change to what is shown on the eval kit?

or maybe you can recommend a more 'stable' buck boost converter for an input of at most 6V.

thanks.

  • 0
    TI__Guru* 76416 points

    What may be happening is at start up the TPS61202 will draw a large amount of current.  This will overload the bus, UVLO is activated and the device turns off.  When the device turn off bus voltage rises and the device tries to restart and the cycle continues.  

    There is an application note on how to use an external circuit to reduce this inrush.  It is written for the TPS61070 but will work for the TPS61200, adjustable version required.

    http://focus.ti.com/lit/an/slva307/slva307.pdf

     

    Another part to look at is the TPS61220, Vin min is only 0.7V and it is a lower power part.

  • 0 in reply to Bill Johns
    Prodigy 30 points

    Hi 

    I am currently considering using the TPS61200 in conjunction with solar panels. The panels would give me an output voltage of 0.5V - 0.6V. This i will use as an input to the boost converter (TPS61200). I require an output voltage of approximately 5V and an output power between 4W - 5W. I was considering connecting a power mosfet on the output of the TPS61200 but it does not have an SW pin like some of the other converters provided by TI...so that definitely will not work. Another option would be to connect some external LOGIC circuit to the 5V output of the TPS61200 and then have a FET on the output of this LOGIC circuitry to boost the current required to attain a higher power output. I've lloked at app notes regarding the TPS61200 but none of them provide a solution with external driver FET's connected to the TPS61200. Can anyone possibly help me?Any other suggestions on how I can achieve this???

    Thanks..Peace!

  • 0 in reply to Ashley Peters
    Prodigy 40 points

    i dont think you can use external FET for tps61202 since (as i've remembered, kindly check datasheet to veirfy)  it has an internal transisitor. in addition, based of my experience using tps61200, the (boost) conversion would result to a great loss in power. you might want to check this site http://powerelectronics.com/power_management/boost_converter_efficiency_calculations-809/ .

    ive used tps61202 with input from solar panel with rating 5V and 3.3V (ive used different panels for two set ups). Voltage-wise, the converter functions properly. however, current is reduced because of reduced power. I actually dont know how to deal with this that's why we removed our tps61200 circuit in our module.

     

  • 0 in reply to seybyer
    Prodigy 30 points

    Hi Seybyer..

    many thanks for ur help and advice...its much appreciated...U mention that uve removed the tps61200 circuit  from urls module...could u kindly tell me what u guys have used in place of the tps61200 circuit??

    Or is there any other boost converter circuit that i can use that would give me the power out (5Watts) with the small input voltage (0.5V) that im currently looking for?

    I am currently looking for a circuit that would allow me to boost the current from the output if the tps61200 but if it doesn't work as you say then i  am wasting valuable time...

    Thanks bro

  • 0 in reply to Ashley Peters
    Prodigy 40 points

    we removed it from our circuit and instead we changed our panels with a much higher rating. we don't have much time to do the research that's why we settled in that solution.

    regarding your query about a 5W boost converter, i haven't encounter one but if i do so, i'll inform you immediately. Good luck.

  • 0 in reply to seybyer
    Prodigy 30 points

    thanks seybyer....

    please inform me if u encounter anything that will solve my problem...

    i am also running out of time for my project and i cannot keep on researching for days on end...

    thanks again take care

    and good luck!

    Peace!