Research Notes

Options for MPPT/Battery Charging

not AEC-Q100 :(

Option #1: https://www.analog.com/en/products/ltc3130.html +

the LTC3130 is a buck-boost converter that can do MPPC
- it outputs a fixed voltage chosen by a resistor divider (the LTC3130-1 has fixed output voltages)
- we could connect one of these to the output of each solar panel and then connect their outputs together directly to the battery charger input
  - I should figure out why RG SAT thought he needed to use or-ing ideal diodes and multiple MPPT chips but then decided against it and find out if his final design even worked
- the output current up 600mA at 19.3V input and slightly less at 12V input for 12V output . This behaviour improves for smaller output voltages and gets worse for larger ones.
  - battery pack charging voltage is ~8.4V
  - one solar panel outputs 500mA
- we would need a separate solution to charge the battery pack which leads me to …

Options for Battery Pack/Charging

two chargers like this: https://www.batterytender.com/connecting-batteries-chargers-in-series-parallel

MPP

MPPC is a term used by analog deivces: https://www.analog.com/en/resources/technical-articles/techniques-to-maximize-solar-panel-power-output.html but it describes what we want to do
The maximum power voltage (VMP) of a solar panel does not, typically, vary much as the amount of incident light changes https://www.analog.com/en/resources/technical-articles/solar-battery-charger-maintains-high-efficiency-in-low-light.html

Option	Problem
LTC3105	made for single PV cell (max Vin=5V)
not AEC-Q100
LTC3129	max Vin=15V, would need to reduce 8 cell string to 6 cells
not AEC-Q100
LT3652(HV)	battery charger
LTC4000-1	battery charger
LTC4020	battery charger
LTC3130	not AEC-Q100
LTC3119	not available for purchase

LTC3130 Design

Tasks Remaining after Schematic Review

We originally made this schematic for the EPS board, but now we want to print the part on its own instead. Here are the step required to make that happen:

[ ] choose input/output connectors
[ ] update the layout to match the schematic changes
[ ] address the inductor sizing problem (my idea is to put multiple inductor footprints in parallel on the board and then only populate one at a time so we can sweep the inductance value and see what the minimum we can use it)
[ ] print, assemble, and test 🙂