This read me is currently under development
This project is the hardware part of the superior UPS-2 project
https://github.com/ECOM-Engineering/UPS-2_Uninteruptible-Power-Supply.git .
If you are looking for a simple power-down switch, please refer to the s_shut project
https://github.com/ECOM-Engineering/Raspberry-Shutdown.git .
Please refer to the [UPS-2 schematic](./doc/UPS-2 Schematic.pdf).
UPS-2 hardware builds an uniterruptible, efficient power supply with a wide input range. There are no glitches during switching and very low power dissipation resulting in cool operation.
Switching between main supply and backup source (usually a battery) is performed by the dedicated TPS2121 switch by TI with no CPU intervention. This guaranties a seamless switchover between the two power inputs. Furthermore, this design allows high efficiency thanks to the very low 56mΩ on resistance.
5V output voltage regulation is performed by the TI TPS56339 3A buck converter with an efficieny of >94%.
Output is protected by the Raspberry standard 'ideal diode' against back driving, if Rasbperry Pi is powered through it's USB connector.
Please refer to the TPS2121 data sheet
TPS2121 (U2) Power Mux is operated in th 'fast switchover' mode: If input PR1 (derived from Main input) falls below approx. 8V, U2 switches over to the Battery input without CPU intervention. Capacitors C5, C6, C7 remove switching spikes and Voltage drop during switching over. C7 is a low EMC type with enough capacity in order to limit voltage drop during switching at up to 3A output load.
Voltage scaler allows measuring supply voltages by the ADC of the CPU. In order to minimize quiet current of the voltage sources, it uses as high resistors as possible regarding the input bias of the ADC.
System Controller provides
- communication with the user via LED indicators and a switch for manual controlling
- communication with the Raspberry CPU via serial or parallel interface
- firmware flash update via debug port or via Raspberry serial interface
UPS-2 uses an Cortex M0+ CPU of the STM32G030 from STMicroelectronics. This CPU provides an incredible 32Bit performance/price ratio.
Debug connetor J6 uses the SWD serial wire debug and flash programming. Pins 1..4 are compatible with the STM32 eval and diccovery boards.
This memory meets the Raspberry-Pi Hat specification and can be programmed by the user. Currently, this EEPROM is not used and is unprogrammed.
For Jumper Settings and functions please refer to the UPS-2_User Guide
Board outline corresponds to the mechanical Raspberry-Pi Hat specification.
UPS-2 uses a 1.6mm 2-layer PCB.
- KiCad EDA system for schematic an PCB layout.
- Typora for markdown texts (this readme)
- Libre Office for Text and illustrations
- git and github
This project contains all documents necessary for production including BOM with digikey part numbers and Gerber files for PCB 2-layer production.
In order to make production as simple as possible, PCB uses mostly SMD components that may be produced and soldered by nearly any prototyping service (no fine pitch, 0805 resistors, capacitors). First prototypes have been produced in Switzerland by https://www.quick-pick.ch/.
Hardware is licensed under the open source license CERN-OHLW v2 .
Document Copyright (c) 2021 Klaus Mezger, open source under MIT license.