Status: Active

Owner: Zen & Chris

Requirements

• Passthrough 18 V - 55 V (6S lower voltage to 12S upper voltage )

• Measure current through hall effect current sensing (without a shunt resistor to minimize losses)

• Measures voltage with an ADC

• I2C or UART interface

  • Preference toward I2C, but just pick one of them

• XT90 connector for input power and output power

• Maximum current passthrough requirements

  • Max pulsed current 200 A

  • Max continuous current 75 A

• Steps down input voltage to clean 5V and 12V rails

• Refer to Nathan’s current power module, photos in discord, for a reference to what this board will be replacing.

Current Sensing

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https://www.digikey.ca/en/products/detail/koa-speer-electronics-inc/PSL2NTEBL500F/1039674

Block Diagram

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• The 12V output is left as a power pad so that a connector can be soldered onto it and a harness can be made as needed

• The Molex connector is based on the connector standard for the Pixhawk, shown below

• A 5V-3.3V LDO was added to provide a 3.3V rail for the SCL and SDA lines, as per the Pixhawk standard

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12V Buck

IC Selection

Based on price, current limit and efficiency, the LM5012 is chosen.

Typical Application Circuit

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Pinout & Functions

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Switching Frequency

• Higher switching frequency allows for the use of smaller inductors and capacitors as well as lower output ripple, but it comes at the cost of increased switching losses

• Since this application involves a relatively high voltage input, the selected switching frequency is 300kHz, which should provide a reasonably low ripple current while minimizing switching losses

Frequency Setting Resistor

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For a 12V output and 300kHz switching frequency, R=100k

https://www.digikey.ca/en/products/detail/yageo/RC0603FR-07100KL/726889

Implementation Ideas

• “High” voltage & current passthrough should be done with an XT90 connector.

• Current measuring can be implemented with a smaller current transformer to be mounted on the PCB

• A simple ADC integrated (presumably 2 channel ADC) and possibly voltage divider circuit can be used to measure both current and voltage

  • This ADC should support I2C and SPI and may be fitted with a signal buffer IC

  • Fairly standard to be able to find an ADC that can operate at 3.3V

• A single “low voltage connector” should be used

  • This would be some relatively fine pitch connector

    • Some standard molex thing

  • Four conductors on this connector

    • GND (this will be signal ground, but should be presumed as the same potential and non-isolated from the “high voltage passthrough gnd”

    • 5V or 12 V input power (possibly a range that supports each of these and maybe more)

    • I2C or UART data lines (2 conductors for each of these protocols.

• Alternatively, use the 12V and 5V stepped down from the input line to power all board ICs instead of plugging in external power

• Powering the ADC

  • The ADC and buffer (if a buffer is included, just an idea) will ideally consume very miniscule current, on the order of less than 200mA which makes a simple LDO (low dropout regulator) viable

  • This LDO will take the low voltage input power and use that to power the ADC chip.

  • LDO has lower efficiency than a buck, but will save board space and will be more convenient to implment.

    • Because of the negligible total power requirements for the board a low efficiency doesnt matter as much

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