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Solar powered lithium charger with LTC3105 & LTC4071

I would like to implement the lithium battery charger given at https://www.analog.com/en/design-center/reference-designs/circuit-collections/ltc3105-ltc4071-2-cell-solar-panel-li-ion-battery-charger.html#cc-overview.  Battery being charged is Li-Ion 3.7V, 2200mAh.

However, my solar panel measures Voc=5.6-5.8V, and Isc=30-34mA.  Max power point is 4V delivering 100mW.  These are higher output parameters than what is outlined in the design.

My desired Vout is 4.2V for Li-Ion charging, so just a slight boost over the MPP voltage of 4.0V.

Three questions:

1. Will the charge circuit still work?

2. Testing seems to show the IN voltage from the panel drops to roughly 3.4V instead of being held at 4V by the MPPC.  Is this expected?

3. Will the open circuit voltage at 5.6V (above Vin spec but under absolute max) cause additional problems?

It is important that I maximize the energy harvest from the solar panel, which is why I've been looking at parts with MPPC.  Can you suggest parts or full solutions that would be more appropriate?

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  • Hi,

    I think I replied to your comment you asked about LTC3105 in another message. As mentioned LTC3105 will work for Vin>Vout however it will not be efficient. Also your Vin is above the input voltage range. Operating the part higher than the input voltage range specification is not recommended and its behavior will not be guaranteed.

    Instead of LTC3105 you can use LTC3129 which has mppc feature and higher Vin range and would be more efficient for your operating range.

    Thanks  

Reply
  • Hi,

    I think I replied to your comment you asked about LTC3105 in another message. As mentioned LTC3105 will work for Vin>Vout however it will not be efficient. Also your Vin is above the input voltage range. Operating the part higher than the input voltage range specification is not recommended and its behavior will not be guaranteed.

    Instead of LTC3105 you can use LTC3129 which has mppc feature and higher Vin range and would be more efficient for your operating range.

    Thanks  

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