Weekly Summary - Robert Tang
Introduction
Brief documentation of what Robert Tang has been up to each week to help in synthesis of final report and so @Kevin Li can visualize where the time is going and help resolve roadblocks. Formatting is expected to be similar to Weekly Summary - Meghan Dang.
Table of Contents
Related Resources
Weeks
Week 1
Started and completed the Electrical Bootcamp
Carried out component selections, selecting resistors, capacitors, diodes, LDO IC to make a LDO regulator that converts 12 Volt to 5 Volt
Created footprints for the LDO IC and LED, and created schematics and PCB layouts
Applied methods such as polygon pouring, carefully selecting via placement to maximize the efficiency and effectiveness of the 4 layer PCB board created
Researching about linear regulator and started looking into the project beginning next week (Week 2), which is buck converter.
Week 2
Started the project (24V to 5V at 5A buck converter)
Learnt about how a buck converter work, and more details into buck converters, such as CCM, asynchronous and synchronous buck converters.
Started selecting components for the buck converters
Selected buck converter IC (MPS)
Selected input capacitor
In the process of selecting an inductor, looking at inductor values between 4.7uH to 6.8uH
Started designing schematics
Imported WARG template, and power ports connection
Created footprint and symbol for buck converter IC
Placed the input capacitor (from WARG library)
Week 3
Finished the schematics, the schematics is sent to Meghan and Kevin for review
Buck converter part:
Implemented input and output capacitor network (carried out calculation and selected components from the library)
Feedback voltage network implemented (0.5V V_FB)
Added all other components
Reverse Polarity protection
Research different methods of RPP
Diode, high side PMOS, low side NMOS, Driver IC and high side MOSFET
Selected a Driver IC (LM74700QDBVRQ1) and according to the datasheet selected the NMOSFET
Created symbols and footprint for the IC
Implemented the circuit in the schematics
Adjust the finished schematics based on comments
Started doing the layout, and getting the necessary formats of the PCB board
Imported the layer stackup and design rules
Week 4
Updated schematics
Added comments to the schematics
Changed components
LED circuit: 390R to 1kR for a smaller current
Added 2*10uF caps and 0.1uF caps for better filtering at the RPP circuit
Modified NMOS symbol
Started and finished placement
Placed the components, carefully considering the signal integrity
Detailed comments can be found in the 24V-5V design document
Started routing
Week 5
Updated placements:
Update the connector to the correct one
The new connector is huge to compensate for that I shifted most components to the left a bit
Fixed small footprint issues
Almost finished routing
Connected V_BAT, V_BAT_PROC, 5V0 rails with big polygons
Doing a 4-layer PCB (signal/power+GND+GND+signal/power)
For 5V0, route to L4 first and then up to L1
Changing the thermal relief for certain pads
Placed GND stitching and GND pour on L1 and L4
The other routing details can be seen in the PCB doc and the design doc
Week 6
Chill week
Fixed small issues on the PCB to make the board looks good
Tried to start a PDN analysis
Need to account for:
VBUS: Input connector -> NMOS, NMOS -> Buck IC
SW: Buck IC -> Inductor
5V: Inductor -> Pixhawk Conn, Inductor -> USB-C Conn, also do Inductor to farthest decoupling cap down (basically before the via punch down to L4).
Started looking at the next project
Pre-charge circuit
Week 7
24V to 5V @ 5A Buck Converter
Adjusted layout for better appearance
PDN analysis:
Encountered some issues, finally calculate the impedance by voltage drop over the current
The screenshots are updated in the design document
12s Pre-charge Circuit
Defined system block diagram
Researched about what pre-charge circuit, CAN interface, and current/voltage sense
Looked at options for pre-charge IC, currently reading the TPS48111 IC
Week 8
Buck:
Components and layout reviewed
Added bottom layer silkscreen and exported the Gerber file for fab
Verified selected Pixhawk connector’s compatibility with the harness
LED Board harness (helped work session)
Board review (6s to 5V buck)
12S Pre-charge
Looked at the TPS chip thoroughly for understanding how it work
Looking for more options for the pre-charge ic
Implement the STM32 MCU and the CAN circuit for the CAN adapter board
Week 9
24V to 5V Buck:
Added bottom layer meme
Export Gerber files and have it verified
Add to order in JLCPCB (midterm order)
12S Pre-charge:
Selected pre-charge IC (TPS48111 chip)
Implemented symbols and footprints
High level system architecture defined
Started looking at options for powering the STM32 (12S to BUCK to LDO to 3.3V)
Week 10
24V to 5V Buck
Saved to Github
12S Pre-charge
Schematics
STM32 and CAN circuit implemented and updated pin connection according to design
Pre-charge circuit implemented
Pre-charge IC footprint and symbol changes (to make the whole schem look good)
Implemented all functions except for the input GPIO pins
STM32 power archeitecutre
BUCK + LDO, buck circuit (12S battery to 6V Buck and 6V to 5V LDO)
Week 11
Ordered 24V to 5V Buck PCB
12S Pre-charge
Schematics:
Added CAN connectors, modified LDO to a smaller size, modified pre-charge FET.
Layout:
Placement roughly done, needed review
Started routing (the main power path)
Week 12
Finished first rev routing for 12S Pre-charge board
Finished routing the main path (VBAT to FETs to VOUT), pretty optimal
Made the LDO+BUCK power architecture more compact
VBAT-RPP-BUCK-LDO-3.3V
Removed some of the CAN components to make the routing more differential
Added SWD connector for programming the board
Helped bring up the water controller, gained knowledge on how to apply solder paste on the PCB
Week 13
Buck order has arrived at the end of week 12, started assembling them this week
Assembled 2 boards first for testing
1 board worked all right, used that for testing
Power efficiency testing: bypass the RPP circuit, and use wire connection instead of USB-C to the eload, to get a efficiency around 90% at 5A output
RPP testing: reversed the polarity of the input connection, the board shuts down, when plugged in the correct direction board worked.
The other board have some issues.
Buck IC and Inductor are shorted to Ground
Smoke coming out of the board when powered with 24V
BUCK IC was shorted perhaps during assembly, replaced the BUCK IC and the board was working again
Assembled the rest of the 3 boards on Friday
After debugging and cleaning up on the boards, 2 of them worked without issues (tested max current draw of 5A with eload, and tested the voltage output)
1 doesn’t work because I ripped the copper off, the pcb board itself is damaged, will need to check next week
REV2 of the 12S Pre-charge board
Added current sense trace, made changes to the layout as per Kevin's review, doubled up power polygons (vias)
Week 14
Waveform capturing on the buck converter
SW, FB and VCC nets
12S Pre-charge board
Keep working on layout
Fixed schem.