Battery Charger: LTC4010
- for best reliability, input voltage should be (2V*n_cells)+0.3V = ~21V
Undervoltage Protection: LT6703-2
- 1.4-18V voltage comparator with built in reference
- V- pin exposed, will output a logic 1 if input < reference
- low current draw, ~6.5uA
- open collector output, will likely need FET driver
Boost Converter: TPS55330
- 12V to 21V boost converter
- 1.5A output current
Load Switch:
- 2A-5A (higher end of the range is better)
- battery voltage can be ~14V, so voltage needs to be >14V
- active high enable
- WSON package for better power dissipation
- may need to be a high side MOSFET driver + power MOSFET
Best load switch we could find: http://www.ti.com/product/tps22810
- 18V max Voltage
- 3A max Power
79mΩ Ron
Or we can use an NMOS and a Power PMOS in the following manner:
Here, Q1 will an NMOS that feeds to the gate of Q2.
- 5A continuous drain
- 20V drain to source voltage
- Ron = 45 mOhm @ 4A, 4.5V
OR Gate:
- actually needs to be a NOR gate (inverted or), since a logic 1 at the output of the OR gate should turn off load switch
- able to take battery voltage on power supply, or pair with regulator that drops battery voltage to logic voltage
- 5V or 12V logic compatible (12V preferred)
- SOT package preferred
System Block Diagram:
