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Based on price, current limit and efficiency, the LMR38020 is chosen.
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12V Buck
Requirements
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 |
|---|---|---|---|
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 |
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https://www.digikey.ca/en/products/detail/yageo/RC0603FR-07100KL/726889
Output Inductor
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Choose k=0.4 for current ripple
Expected current draw from the load is 500mA, design for 750mA to be safe
This gives L=67.1uH
Choose closest standard value, 68uH
Inductor saturation current should be >= Isc , the high side switch current limit of 3.2A, to avoid component damage due to high current when the inductor saturates
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https://www.digikey.ca/en/products/detail/koa-speer-electronics-inc/PSL2NTEBL500F/1039674
Pullup Resistors x3
https://www.digikey.ca/en/products/detail/yageo/RC0805JRRC0603JR-0710KL1010KL/72824113694233
Decoupling Capacitor
https://www.digikey.ca/en/products/detail/murata-electronics/GCJ188R71E104KA12D/7363221
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