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Newbie level 1
Hello,
I'm designing an buck converter that operates from a stable 12V DC source and makes it into 6.3V 8A DC.
I'm trying to prevent using IC's i can't solder(newer packages that require reflow etc, unhumanly small).
So i found LTC1625 from Linear technology which suits my needs.
But it's datasheet isn't as good as TI's for example and i'm running into problems, mainly into picking capacitors for input and output.
Basically i am between two mosfets: SI4410DY and Si4134DY. I'm probably going to order both. SI4410DY is easier to design because i downloaded LTSpice and it had SI4410DY in database but no Si4134DY.
Calculations i have made according to datasheet:
Pt(100)=1.3 [temperature related RDS on changes, using SI4134DY]
RDSon=0.120/8*1.3=0,0115ohm
Ptop=0.60W [Top mosfet power dissipation]
Inductor=7uH
Tjunction=70C+0.6*50=100C (I presume this is the maximum Tjunction, is it really realistic for the IC to have 70C ambient as is in datasheet?)
Resistor divider: R2=35.7kOhm ; R1= 8,3kOhm 1% (Should give 6.3V)
Supply is probably going to drive around 6A but 8A would be good. I don't mind losing on efficency and the components could be quite big.
Now i'm stuck at finding the required input and output capacitors. The datasheet says to use RMS but they don't show good calculations so i'm stuck...
According to Irms=Iomax*Vout/Vin(Vin/Vout-1)^1/2 so if i put my data in Irms=4A, how do i choose capacitor now? I understand that the capacitors combined peak rating must be higher than 4A, what about capacitance and voltage? I presume this is for the Cin capacitor solely.
For Cout i presume i use the formula Vmaxrippleiwant=Ilmax*ESR . So if i want ripple 0.05V then 0.05=3.2*ESR ESR=0,0156ohms? But how would i choose the voltage and capacitance?
Also what would be good software to design this IC, i have eagle cad for student but i think even windows 10 search is better than that... Maybe have to manually insert the package...
I'm designing an buck converter that operates from a stable 12V DC source and makes it into 6.3V 8A DC.
I'm trying to prevent using IC's i can't solder(newer packages that require reflow etc, unhumanly small).
So i found LTC1625 from Linear technology which suits my needs.
But it's datasheet isn't as good as TI's for example and i'm running into problems, mainly into picking capacitors for input and output.
Basically i am between two mosfets: SI4410DY and Si4134DY. I'm probably going to order both. SI4410DY is easier to design because i downloaded LTSpice and it had SI4410DY in database but no Si4134DY.
Calculations i have made according to datasheet:
Pt(100)=1.3 [temperature related RDS on changes, using SI4134DY]
RDSon=0.120/8*1.3=0,0115ohm
Ptop=0.60W [Top mosfet power dissipation]
Inductor=7uH
Tjunction=70C+0.6*50=100C (I presume this is the maximum Tjunction, is it really realistic for the IC to have 70C ambient as is in datasheet?)
Resistor divider: R2=35.7kOhm ; R1= 8,3kOhm 1% (Should give 6.3V)
Supply is probably going to drive around 6A but 8A would be good. I don't mind losing on efficency and the components could be quite big.
Now i'm stuck at finding the required input and output capacitors. The datasheet says to use RMS but they don't show good calculations so i'm stuck...
According to Irms=Iomax*Vout/Vin(Vin/Vout-1)^1/2 so if i put my data in Irms=4A, how do i choose capacitor now? I understand that the capacitors combined peak rating must be higher than 4A, what about capacitance and voltage? I presume this is for the Cin capacitor solely.
For Cout i presume i use the formula Vmaxrippleiwant=Ilmax*ESR . So if i want ripple 0.05V then 0.05=3.2*ESR ESR=0,0156ohms? But how would i choose the voltage and capacitance?
Also what would be good software to design this IC, i have eagle cad for student but i think even windows 10 search is better than that... Maybe have to manually insert the package...