Open source design files for the LT3652 Power Tracking 2A Battery Charger can be obtained from Circuit Maker. Circuit Maker is a free PCB design tool from Altium. Designs can be imported into Altium Designer.
A PDF version of the schematic can be obtained here.
This project is based on a Linear Technology LT3652 Power Tracking 2A Battery Charger for Solar Power.
Featuring a wide 5 to 32V input range and input supply regulation loop for peak power tracking, this battery charger suits Li-Ion/Li-Polymer, LiFePO4 and SLA Chemistries with a programmable maximum battery voltage of 14.4V and a maximum current of 2 amps.
The current schematic design is for a 2A, 12V SLA charger with 13.8V float.
The R1/R2 voltage divider sets the maximum power point voltage to 17.2V. The maximum charging current is reduced when the input voltage is below 17.2V (VIN_REG pin is under 2.7V). Set this voltage divider to your PV Panel’s VMPP.
The maximum charging current is set by R3. A 0.05 ohm shunt sets the maximum charging current at 2A, the maximum current possible from the LT3652.
The R6/R8 voltage divider sets a battery voltage of 14.4V. R6 should be selected to obtain a 3.3V input on the VFB pin. This pin has an 110nA input bias that can be compensated using a voltage divider with a 250k equivalent resistance. R7 is calculated to compensate the network and obtain this 250k equivalent resistance.
R9/D7 are optional and can be used with sealed lead acid batteries to set a float voltage after C/10 has been reached. i.e. for a 12V SLA battery, the initial battery voltage can be selected to be 14.4V, and this reduces to a float voltage of 13.8V once C/10 is reached and the CHRG LED is extinguished.
The boost pin is used to bootstrap the internal switch gate. It has an operational range of 0 to 8.5V. As such, 6.2V Zener D3 is used to reduce the potential on the boost pin.