A 5V, 2.5A Uninterruptible Power Supply based on the Linear Technology LTC4040 2.5A Battery Backup Power Manager. The LTC4040 includes a step-up DC-DC converter to power your 5V equipment from a single cell Li-Ion or LiFePO4 Battery. When external power is available, the step-up regulator operates in reverse as a step-down battery charger.
Battery chemistry and charge voltages can be set up with F0, F1 & F2. For Li-Ion cells, regulated charge voltages of 3.95V/4.0V/4.05V/4.1V are available. For LiFePO4 cells, 3.45V/3.5V/3.55V/3.6V is possible. As the batteries are used for back-up purposes and as capacity is degraded when cells remain fully charged, it is recommended to trade of capacity (up-time) for battery lifetime.
A fixed resistor on the PROG pin, sets the maximum charge current. The current design uses a 2K resistor to set the charge current to 1A. The LTC4040 includes a safety timeout or approximately 4.25h for Li-Ion batteries and 2.13h for LiFePO4.
A current shunt can prioritise system load over charge rate, ensuring the input power supply is not overloaded.
D2, D3, D1
R5, R6, R7, R13, R12, R11, R2