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
RES SMD 324K OHM 1% 1/8W 0805
RES SMD 1.69M OHM 1% 1/8W 0805
CONN RCPT USB 4POS UNIV SERIAL
SiR172DP Series N-Channel 20 V 0.0074 Ohm 41.7 W SMT Mosfet - PowerPAK® SO-8
Samsung Electro-Mechanics 100F 20% 10 V X5R Dielectric SMD Ceramic Multilayer Capacitor 1210
RES SMD 174K OHM 1% 1/8W 0805
RC Series 0805 0.125 W 1 kOhms 1% ±100 ppm/°C SMT Thick Film Chip Resistor
R8, R9, R10