Definitive Tracking Antenna Design Decisions

Buck converter IC:

https://www.digikey.ca/en/products/detail/alpha-omega-semiconductor-inc/AOZ2261NQI-12/16265489

Input bulk capacitor:

https://www.digikey.com/en/products/detail/murata-electronics/GRM21BZ71H475KE15K/13904908

Input decoupling capacitor:

https://www.digikey.com/en/products/detail/murata-electronics/GCM188R71H104KA57D/1641653?s=N4IgTCBcDaIOIGECyBGAHGgSgdhQCRQAYAWAaQEEBWbAERAF0BfIA

Output inductor:

https://www.digikey.com/en/products/detail/eaton-electronics-division/DR125-6R8-R/667158

Output capacitor:

https://www.digikey.com/en/products/detail/murata-electronics/GRM32ER71A476ME15L/2548479

Bootstrap capacitor:

https://www.digikey.com/en/products/detail/murata-electronics/GCM155R71H104KE02D/4903704?s=N4IgTCBcDaIOIGECyBGArGgSgdhQCRQAYAWAaQFFCwAREAXQF8g

VCC input capacitor:

https://www.digikey.com/en/products/detail/murata-electronics/GRM188R6YA475ME15D/4905370

Feedback resistors:

https://www.digikey.com/en/products/detail/yageo/AC0603FR-1310KL/13694194

https://www.digikey.com/en/products/detail/yageo/RC0603FR-0773K2L/727374

Overcurrent setting resistor:

https://www.digikey.com/en/products/detail/yageo/RC0603FR-078K2L/727390

Frequency setting resistor:

https://www.digikey.com/en/products/detail/yageo/RC0603FR-13470KL/13694191

Set lower resistor value R2 = 10k

Open

R1=73.2k

Select Fsw to be 470kHz. Mid range switching frequency that is a balance between switching losses and improved smaller ripple and inductor.

Input caps should be rated for 50V (about 2x max VBAT to protect against SW node overshoot)

Put a 0.1uF decoupling capacitor on input to filter out high frequency noise.

Use Eq below to calculate input capacitance requirement

Let allowable voltage ripple be 2% of Vin (0.02*25.2 = 500mV pk to pk)

Iout = 5A

f = 425kHz

Vout = 5V

At max VIN (6*4.2=25.2V), Cin ~= 3.7uF

At min VIN (4*3.2=12.8V), Cin ~=5.6uF

At 12.8V and 25.2V, about 3*4.7uF, 50V caps should provide enough input capacitance.

Put 4.7uF, 35V MLCC connected to VCC

The inductance is calculated first

Let current ripple deltaI be about 0.4*5A=2A pk to pk

f = 425kHz

Vout = 5V

Vin = (Vin_min + Vin_max)/2 = (12.8+25.2)/2 = 19V

L = 4.3uH

Current 6.8uH inductor would give 1.27A deltaI pk to pk or 25% current ripple. We should be good to keep inductor as is (see linked inductor)

Saturation current should be greater than 5A + 1.27/2A = 5.635A. Current inductor has saturation current of 6.64A, should give enough buffer even with tolerance and temp derating.