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September 6, 2010
To make this work you would have to enable to MPPT function by adding a resistor divider on the Vin_Reg pin, or by greatly increasing R1 to limit your charge current. The solar panel you mentioned is just a little under powered for what this chip wants to do. If Sparkfun make a breakout board for the LTC3331 that would be much better.
The charge current is set by resistor R1 (0.22Ω). Normally max charge current is Ichg = 0.1/Rsense. So perhaps you could change (reduce) it, but I’m not sure what saturation current the inductor has. You need to make sure you stay below that with some room to spare. The LTC demo board uses a 0.05Ω resistor and an inductor with a 7A saturation rating.
Perhaps you could copy what the Linear Tech evaluation board did, and add a jumper that engages a voltage divider on the Vin_Reg pin, see JP4. Without this, the LTC3652 doesn’t do its version of MPPT, it is just a nice high voltage switching battery charger.
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