Introduction

• Who

  • Andrew Chai Engineer

• Background

  • Something like

    • https://p-systems.io/product/power_module

    • https://store.p-systems.io/products/power-module?variant=41060173086897

• What

  • 30.5x30.5mm mounting pattern

  • 5V @ 4 A buck buck capability

  • high current pass through with 2x XT60s

    • 100 A pulsed current capability

    • 60 A max continuous current capability

  • pre accurate current sensing

  • Use the custom CAN circuit designed for ESC CAN Adapter .

    • EFS would need to dev for it but nws.

  • Single JST GH four pin to CAN x port on pixhawk

  • Balance Lead Connection

    • Measuring each cell voltage would be nice as well to improve SoC calculation.

    • would need 2x headers if we run two 6S batts in parallel which seems to be POR as of June 2024 for Fixed Wing 2025

  • Stretch requirement: Active balancing (Can be done, some extra circuitry required and must be taken into consideration in regards to component sourcing and which IC to use)

    • could be cool if there’s board space for it, hmm extra weight and risk tho, maybe not, EE lead thoughts

    • more work for firmware to develop cell balancing algorithm

    • save for next rev probably

  • Input Voltage Range: 26V to 12V

• Target Use

  • Would be for Fixed Wing 2025 .

• Why

  • few COTS options with CAN

  • few COTS options with 30.5x30.5mm mounting pattern

  • Fun for EFS dev, opens doors for more complex SoC calculation

Electrical Architecture

Features:

• Buck + LDO (Power Module)

• Current Sense

• Active Cell Balancing

• Cell monitoring and measurement (SoC calculations)

• MCU for custom cell balancing algorithm + cell input calculations + interfacing with IC

• CAN circuitry

Elec System Design

Component Sourcing

• Buck:

  • https://www.digikey.ca/en/products/filter/power-management-pmic/voltage-regulators-dc-dc-switching-regulators/739?s=N4IgjCBcpgTAnFUBjKAzAhgGwM4FMAaEAeygG0RZYB2MeWEAXSIAcAXKEAZTYCcBLAHYBzEAF8iAVmoBmJCFSRMuQiXLgAHABZJ8DSCJgNANi1gADAc0aNdK3XOSL9%2BubCSXW7Vpezqlwz1qeGMrWHNzWDgwt0kNBiIoyRlHJlYOSG4%2BIVEJcGpg%2BUVlfCJSSApYLXgwWjSQdk4eARFxMTEgA

  • Filter for voltage regulators rated between 30V-40V max input voltage (larger than expected 26V), 4A output current, and 5V output voltage

  • https://www.digikey.ca/en/products/detail/alpha-omega-semiconductor-inc/AOZ1284PI/3973647?_gl=1*1btu0z8*_up*MQ..&gclid=CjwKCAjwnK60BhA9EiwAmpHZw27SU0BE88KlHdxr9NsAO4rO5YNk5dtL7PkYqBgAR_-V20XOpyAJpRoCcAUQAvD_BwE

    • 3V to 36V input voltage range

    • up to 95% efficiency

    • 4A continuous output current

    • adjustable switching frequency

    • adjustable output voltage (0.8V to 30V)

      • Vout = 0.8 * (1 + R1/R2)

      • 5V output requires standard resistor values of: R1 = 52.3k, R2 = 10k (recommended from datasheet) this yields around 4.984V

      • alternatively, R1 = 53.6k yields around 5.088V

      • Even better, 10.5K, 2K gives exactly 5V (strange that this was not recommended by the D.S)

      • “The combination of R1 and R2 should be large enough to avoid drawing excessive current from the output, which will cause power loss”

      • given this case: 105k and 20k would also be ideal

      • standard resistor values source: https://www.rfcafe.com/references/electrical/resistor-values.htm

  • AOZ1284PI Buck Design:

    • Exposed Pad (Vin Exposed pad - pin number on symbol??? is this ok in general for a vin pin to be an exposed pad?)

    • What should I use for switching frequency? From what I’ve seen online, higher switching frequency means I can use smaller inductors and capacitors but increases losses.

    • 

    • Using a 100k resistor for 500kHz of switching frequency

    • 

    • Soft start Pin: “A soft start process begins when the input voltage rises to 3V and voltage on EN pin is HIGH. In soft start process, a 2.5µA internal current source charges the external capacitor at SS. As the SS capacitor is charged, the voltage at SS rises. The SS voltage clamps the reference voltage of the error amplifier, therefore output voltage rising time follows the SS pin voltage. With the slow ramping up output voltage, the inrush current can be prevented. Minimum external soft-start capacitor 850pF is required, and the corresponding soft-start time is about 200µs.”

      • will be using 10nF cap, was available on the WARG component library (relatively similar value)

• Cell Monitor IC

  • https://www.digikey.ca/en/products/filter/power-management-pmic/battery-management/713?s=N4IgjCBcoMwGxVAYygMwIYBsDOBTANCAPZQDaIMAnAOxwBMIhV11MjFlAHJQAztW8%2BTSrwCs-EWAaEpYACxghIaqOp05lEAF1CABwAuUEAGV9AJwCWAOwDmIAL6OgA

  • https://www.digikey.ca/en/products/filter/power-management-pmic/battery-management/713

  • https://www.digikey.ca/en/products/detail/analog-devices-inc/LTC6810IG-2-3ZZPBF/9658988

  • https://www.digikey.ca/en/products/detail/rochester-electronics-llc/AD7280WBSTZ-RL/12102176

  • https://www.ti.com/product/BQ76952?bm-verify=AAQAAAAJ_____84hAJ8NJ5_BycGi-Yrn59b_1msRiG6fRmhHUSiBC6aDqGa98i8RWsSF98Aj-Xo8jIN0fN2hwGAmJmzHLewIK74W-5tLc2wlH0ReluO6MvxTB7Ma71vdbcpDfP1ss16IZQiYg4-BsEnTGjWBcXNVGAMMO9jHVWsOJkdsIjOXusuRGOXGOdw6XHabzrknTH2tvpkpmz2Sd_mTL_aHYv6a5toRFRJoyXq3GWQP859SV9Exslm_TjcPp_ADQoAR4FM5orZu_Ro47pHL8BWuTBZKDitqrhxIvJ5RGn5QRbnjB0OicK4npIhbBqaJF0rEnsw

  • https://www.ti.com/product/BQ76925?bm-verify=AAQAAAAJ_____yeqGJxr-sav90uZifqJxu9hEbn3uSR3ocgXRjnzBfqXRBsnLKg0G6dFJQ7CCGSgRfQ4NjwlwddNnfIP8MrH20wHDUOtkq7nb3h5Bhr1LKAijTue-IrMucncEvLeHCkJirMdWhFdYCmuwHorrL0BqOZuGjDWDCVg_XeDQQ4qWXlwj6xY3bVCAfrgJGj6BsGqlZbNkutugz6UEd72EaRjg48vbwkjc4HGktvDajEvwnKhsfbr-YvMg7b9mhPX7NAyC3ItCJkk241i4D5M5VQTmbeYXnGZYhhfJ9JQgs9IhUr-SIz0RdIZTZLcmcutgEk

    • 3-6s cell monitoring

    • no ADC (connect to MCU and use that one)

    • Current Sense

Some thoughts:

• Still not exactly sure how the cell monitoring should be handled, a BMS chip is kinda what I’m thinking or at least some sort of cell monitoring device. An issue I have right now is component sourcing since digikey’s search is yielding some fraudulent results (I think links 1 & 2 for the BMS) since most of the ones that say they can support up to 6 cells (from analog devices) really only support 2 Li-ion (I’m assuming this is the type of battery WARG uses).

• The LT6810 chip seems really ideal but it operates SPI/I2C and is the master node in this case (is this alright?!?! I would expect this kind of peripheral to be the slave node in this case)

• Most cell monitoring ICs are rated for more than 6 cells (usually 8-12) so I don’t think that is a huge problem that some pins won’t be used (redundant not optimal :0), almost none of them have a CAN bus serial protocol so I’ll need to use an IC to convert the signals most likely

• Also, in a perfect world I would use the same IC to monitor current and cell voltage but most chips I have found only operate on one of the functionalities

• Using two separate IC’s (one for BMS one for current), how does data transmission work if both are sending data on the line?

• Optimal IC I think would be the BQ7692, might be wrong here but I think it has current sense capabilities