Voltage regulator on MAX1649

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konradIC13

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Hello,

Recently i got in my hands nice DC-DC step down regulators MAX1649. They are LDO, Vout preset at 5V and they can work with loads up to 2.5A

However, im quite hopeless to design a circuit to make this chip work, in its datasheet
https://www.electro-tech-online.com/custompdfs/2013/02/MAX1649-MAX1651.pdf
there is some kind of typical operating circuit however there are no parts values there :/
And i cant seem to find out how to pick parts (Capacitors, inductors, resistors and diode) to make it work with 5V output and up to 2.5A current.

Did anyone of you used those chips before?
 
What is the input voltage? You will have to buy a rather specialized inductor, a Schottky diode, and a PFET
 
i got PFET already, that was easiest part (it had just to be logic lvl for enough voltage and current), input voltage will be from 6.4V to 8.4V (li-pol 2260mAh 7.4V 2S1P 25C)
 
If you look towards the end of the data sheet (pg. 8) you will see a design procedure and circuits with parts values. Did you read that?
 
Ok i just closely read it, can someone please look at it, it took me some time to get those chips so i dont want to fry them :0

Im using typical operating circuit from first page for MAX1649, connected like that it will work as fixed 5V output.

Resistor from V+ to CS (this is current sense resistor Rsense?). My minimal input voltage will be 6V and maximum load current will be 2.5A , checked figure 5a to find out rs=0.030 (is this ohms?) so ill need resistor with value of 30 mili ohms (+/-5%)? (do resistors have current rating??). Its suggested to have low inductance. Also i didnt noticed anywhere what Watt rating should have that resistor :/

Inductor between output and pfet. It is recommended that it should be between 10-68 uH. I can check its minimal value. Ilim in worst case scenario will be 0.140V (Vcs)/0.030 (rsense)=4.7 A?. It says to set ΔI=0.1 for an overshoot of 10% (i dont know what does it mean) so my minimum L is (with maximum input 8.5V) 2uH (its suggested greater than 10uH so i dont know what to pick, it should be higher than 10uH but how high? :/ Also inductor has to be rated for 4.7A (Ilim)

Diode fast switching schottky with rating for Ilim and Vinput max.

Switching transistor is explained very well , it will be most likely SUP90P06-09L, is it good?
https://www.electro-tech-online.com/custompdfs/2013/02/73010.pdf

Input bypass capacitor. It says that it should be low ESR, on schematic its electrolytic capacitor but then i datasheet it says "Bypass the IC separately with a 0.1 micro farad ceramic capacitor" So the capacitor should be electrolytic or ceramic? And value 0.1 micro farad? I dont know what to pick.

Output capacitor. LOW ESR, electrolytic, what value? It does not say :/

Ref Capacitor. 0.1uF or larger (how much larger?)
 
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