Introduction

• Background

  • Target use for Fixed Wing 2025

  • Buck converter can be designed smaller than 12S Servo Module because of lower input voltage.

• What

  • Same current limiting circuits as 12S Servo Module

    • 4 Channel

    • Leverage the validation we’re already doing on this PCBA as much as possible

  • Common CAN circuit from ESC CAN Adapter

  • Buck Converter for 6S to 5V

    • Could be copied from Tracking Antenna Nucleo Shield Arch using AOZ2261NQI-12 though maybe higher switching frequency. Test this chip on the previous board if possible, cc @Jerry Tian.

  • Keep 30.5x30.5mm mounting pattern from Mounting Hole & Pattern Specifications

    • using 61x30.5mm mounting pattern for ease of routing and to keep all components on one side

  • Current Sense

    • just on the input current would be nice, get some metrics as to how much current the servos require during maneuvers and we already have a CAN line so why not!

  • Target all components on a single side of the PCBA for easier assembly & mounting

• Why

  • 12S Servo Module has some room for optimization for this airframe

    • no CAN support

    • buck converter could be made smaller and lighter since lower max input voltage

• Who

  • @Meghan Dang to take this up July 2024 as lead engineer

  • @Daniel Puratich guidance and review for architecture & design

• Link

  • https://warg.365.altium.com/designs/7B43FD95-910B-4734-8E93-0F4806D2D4FE#design

Engineering

• @Meghan Dang to fill in details

System Block Diagram

Power Block Diagram

Needs Assessment

• Steps down 6S battery voltage to 5-6V to supply servos

• Cut off power to servo if it fails

• Convert CAN from pixhawk to PWM for servos

Requirements

• Supports 18V~28V for 6S battery (rough calcs, 3V-4.6V max per cell)

• 3x4 header inputs & outputs

  • Input:

    • CAN, GND from PIxhawk (creating own 5V PWR)

  • Ouput:

    • PWM, PWR, GND

• 30.5mmx30.5mm board to comply with Mounting Hole & Pattern Specifications

Components

notes:

• input cmc ← perhaps not needed, check 12s doc to read why they implemented

• current sense

  • use INA180 unless determined otherwise

  • shunt resistor: calculate for it? to be looked up

• buck converter

  • check if existing solves, check for board space

  • if not, make buck with lower input voltage & smaller inductor to maximize board space

• LDO

  • does current one from can circuit solve? if not look for other one

  • purpose is to reduce noise from buck.. consult esc can doc for details

• diode

  • what kind of diode… to be looked up

• current limiting eFuse

  • current ones probably solve, however finding a singular IC with 4 channels instead could be better → maximizes board space

  • try and do some component selection here; will probably ask more questions

  • determine whether 4channel efuse vs 4 individuals will be better

    • things to consider:

      • cost

      • board space

      • power dissipation probs not super critical

      • if 4 channels exist for this purpose

• thermistor

  • not sure how to select one, will see later, not super high priority

Buck IC

• AOZ2261NQI-12

• does this solve??

  • yep

inductor selection

• switching freq

  • 600-800kHz

• inductance

  • anywhere from 4.6-5.5 ish

    • lower value, higher fsw based on EQ below

      • range also changes with input voltage, using typ of 22.2V

  • https://www.digikey.ca/en/products/detail/taiyo-yuden/LSXBH10050HL4R9N/16663531

  • https://www.digikey.ca/en/products/detail/bourns-inc/SRN8040TA-4R7M/6155126

  • https://www.digikey.ca/en/products/detail/pulse-electronics/BWVS008080404R7M00/12141054

  • https://www.digikey.ca/en/products/detail/tai-tech-advanced-electronics-co-ltd/HPC-8040NV-4R7M/17835863

Open

Current Sense

• INA180A3

  • 100V/V gain

• shunt resistor

  • 220mOhm

  • should do additional calcs?

  • ask abt this

  • PA2512FKF7T0R1E

• RC filter (output) .;

  • 1kHz cutoff

  • use formula from datasheet

  •  

• RC filter (input)

Open

• f = 1kHz

• Cf set to 1uF

  • size cap to be

Current Limiting IC

https://www.digikey.ca/en/products/detail/texas-instruments/TPS4H160AQPWPRQ1/6175214 choice (for now)

• Source

  • 6V from buck

• 4-channels

• Passives

  • 15k pullup on fault pin

  • Cin

    • TBD

  • Cout

    • TBD

  • 50k to gnd on RLIM

• ^for old IC

• Overcurrent limit for eFuse

  • if possible, implementing adjustable current limit using microcontroller could be the play

    • this would require using a combination of EN and ILIM pins (perhaps also FAULT pin)

    • put notes from datasheet here:

• Passives

  • R(CL)

• = 0.8 x 2500 / 1A

• V(CL) & K(CL) can be found in data sheet

• R(cl) = 2k

CAN Circuit

• lowkey look into how microcontrollers work

• how do they get info from voltage input?

  • using ADC pins

• connect voltage divider VOUT to ADC pins then efs interprets that data omg so awesome

• i removed OSC_EN and

Thermistor

• NTC Thermistor

  • bc they’re pretty standard and faster than alternatives

• 10k

  • because it’s pretty standard?

  • makes readings more accurate probably

  • used voltage divider to get 3.6 or 5 for mcu pin

• 0603

• operating temp

  • -40 ~ 125 C

based on this graph, selected 10k and another 10k normal resistor for voltage divider, @ 25C outputs 3V which the MCU pin can read, at ~40C voltage divider outputs 4V, max that MCU can read

Diodes

• Purpose

  • OR-ing bc two sources, don’t want to do current sharing

• max reverse voltage VR

  • around 10V

• selected diode array to save space

• selected 20V and 2A max bc they didnt have anything ~1A or higher at 10V, 2A good safety margin

Connectors

• XT30

  • for VBATT input voltage bc will probably use a harness anyways & takes up less board space

• TSW-104-08-F-T-RA

  • for servo connectors bc 4 channels 1 component, makes life easy

  • taken from 12S Servo Module

• SM04B-GHS-TB(LF)(SN)

  • for can line

Voltage Sense dividers

• https://developer.wildernesslabs.co/Hardware/Tutorials/Electronics/Part5/Voltage_Divider_Practicals/ ← good resource, explained a lot of assumptions that were made throughout design process

• general notes:

  • generally higher resistance resistors make for better power losses and minimal impact on voltage due to load resistance

• kinda made assumptions before reading this and now everything makes sense

• pins should be chosen based on what voltage divider ranges will be

• because thermistor and vbatt voltage dividers have varying VIN/R1 values, they should be on FT pins (5V tolerant) because it gives more room

  • ranges from 3V-7.3V

added caps to all to make them low passes with ~1khz cutoff

LDO

• putting two LDOs in series to drop 6V-5V, and 5V-3V3

• for 6V-5V

  • https://www.digikey.ca/en/products/detail/microchip-technology/MCP1825ST-5002E-DB/1635502

• for 5V-3V

  • reuse LDO from ESC CAN Adapter

LED

not entirely sure what goes into selecting addressable LEDs, are there any firmware impacts i should be considering?

• https://www.digikey.ca/en/products/detail/harvatek-corporation/T3A33BRG-H9C0002X1U1930/15930508

  • seems fine?

  • VIN is 3.3-5.5 but abs max is 6.5V so can be run on 3V3 rail

  • it’s kinda chonky

• going with the one from SSD for now, using logic modifier also from SSD

  • wanna know more abt how the logic thing works

Layout

Placement

following layout guidelines for the most part

choosing not to use separate PGND and AGND pours on buck

• hopefully won’t be too noisy

• will probably be fine

Simulations

Input filtering sim

• resonance peaks at ~10dB which is chill, much better compared to https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2539980265/RCA+Fried+Boards?search_id=2fb11de2-5048-4262-8172-71d5792f14ca which was ~60dB

• won’t explode