Parallel solar panels with LTC3105

Is it possible to parallel solar cells for use with a single LTC3105? Something like below.

A little background: The device is a cube, with solar panels mounted on each face. The idea is that in a given plane, only one of the panels will be illuminated whilst the other is in darkness.

Also, I'm not sure if the diode should be on the SHDN pin as it is an input pin. Can anyone shed some light?

  • +1
    •  Analog Employees 
    on Aug 1, 2019 2:18 PM

    Hi,

    I do not see any reason why you cannot parallel solar panels for your input. However I have a few comments on your schematics. Why have you set your VOUT and MPPC to 5V? What exactly are your design requirements? This part is basically a step up converter and most efficient while boosting. In buck mode the part still works but is not very efficient. Also if your MPPC voltage is around 5V then please check if the input voltage from solar panels is within the operating range of VIN of the specification in LTC3105 datasheet. If the input voltage can be higher than 5.5V then this part is not recommended.  LTC3129 could be another part which could work better in that case.

    A diode in the SHDN pin should not be required however the enable circuit for this Pin should have very low leakage current else the internal pull up resistance in the part will be pulled down and the part will never startup.

    Thanks

  • Hi Anisha,

    The MPP voltage of the solar panel I am using is 5.01V. Vout is not too important, as it is being regulated down to 3V3 later on. 

    Looking at the LTC3105 datasheet, yes, the maximum rating is 6V. It would be wise to change the component as the open circuit voltage of the solar panel is over 6V. 

    The SHDN pin is basically connected to the IO pin of a microcontroller (via an opto isolator). My main concern was that the SHDN pin is an input pin, so the diode would disrupt its function.

    Solar panel http://ixapps.ixys.com/datasheet/slmd121h10l_nov16.pdf

    Thanks

  • 0
    •  Analog Employees 
    on Aug 2, 2019 2:52 PM in reply to SatEE

    Hi,

     

    The input operating voltage for LTC3105 is 0.225V to 5V. 6V is the absolute max rating. The part might not fail till the abs max value however its behavior and performance is not guaranteed beyond the operating voltage mentioned in the electrical characteristics of the datasheet.

    Also as I mentioned before this is a step up converter and works best while boosting. If Vout < Vin , the part will be still be in regulation but the synchronous rectifiers will be disabled and the body diode switch will be closed. This will make the process highly inefficient and it is not recommended as you will not be able to harvest any energy in that condition.

    So as suggested before, LTC3129 seems to be a better match for your application.

     

    Thanks