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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 150 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
Hall Effect Sensor | INA228 IC | |
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Based on the above analysis, using an INA228 IC seems to be a better option for simpler implementation and integration. To minimize the losses with the shunt resistor, a resistance of 0.0005 ohms will be used (the current power module also uses this value). At max current of 75A, the resistor will dissipate 2.8W. To prevent overheating, a nonstandard resistor with a resistance of 0.0005 ohms and a power rating of 8W will be used, such as the one below.
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Steps down 18-55V to 5V
Current limit should be at least 5A
IC Selection
| SIC462ED-T1-GE3 | TPS54560B | BD9G500EFJ-LAE2 |
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Voltage input range (V) | 4.5-60.0 | 4.5-60 | 7-76 |
Voltage output range (V) | 0.8-0.92xVin | 0.8-58.8 | 1-0.97*Vin |
Output current limit (A) | 6 | 5 | 5 |
Efficiency (%) | 94 | 91 | 82 |
Price ($) | 7.32 | 8.03 | 9.58 |
Link | https://www.mouser.ca/ProductDetail/Texas-Instruments/TPS54560BDDAR?qs=gZXFycFWdAMPyxqrm5VZeg%3D%3D |
While the SIC462ED is the best option for price and efficiency, the beast of a chip has 30 pins. Based on simplicity and efficiency, the TPS54560B is chosen instead.
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Steps down 18-55V to 12V
The 12V rail is only used to power the vtx, which has a 500mA current draw. Ideally, the current limit of the buck converter should be closer to 750mA to be safe
IC Selection
| LT8631IFE#PBF | LV2862XLVDDCR | LMR38020SDDAR |
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Voltage input range (V) | 3-100 | 4-60 | 3.8-80 |
Voltage output range (V) | 0.8-60 | 0.76-58 | 1-75 |
Output current limit (A) | 1 | 0.6 | 2 |
Efficiency @ 600mA load (%) | 81 | 92 | 90.5 |
Price ($) | 17.65 | 0.93 | 2.68 |
Link | https://www.mouser.ca/ProductDetail/Analog-Devices/LT8631IFEPBF?qs=oahfZPh6IALt9hCBxhtB7A%3D%3D |
Based on price, current limit and efficiency, the LMR38020 is chosen.
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Given the high current requirement of 150A, consider using multiple shunt resistors in parallel to spread out the power dissipation across multiple resistors.
Single Shunt Resistor | Multiple Shunt Resistors in Parallel | |
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The selected shunt resistor is 0.0002 ohms and rated for 15W. At max current, the power dissipated is 1502 * 0.0002 = 4.5W. The safety margin is over 3x, so it should be safe to use only a single shunt resistor.
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https://www.digikey.ca/en/products/detail/molex/5024940670/2380433
Power Pads
Power pads will be used over XT90 connectors soldered onto board, for the reason of saving weight and space.
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The footprint of the power pads can be derived the known XT90 dimensions. The pitch of the XT90 power pads can vary, but shall not exceed 11.00mm in pitch. The recommended wire gauge for XT90 is 10AWG (https://media.digikey.com/pdf/Data Sheets/DFRobot PDFs/FIT0588_Web.pdf), which is 2.588mm in diameter.
Using measurements from a COTS power module, the pad was around 5mm. The measured pitch was 5.6mm.
Having different sources of measurements and dimensions, the WARG XT90 power pads will be 5mm square pads, with a 7mm pitch for the positive and negative leads. This allows for a balance of space to solder the wires onto, so it is neither tight or spaced too far out.
Previous Research
Implementation Ideas
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