Hi I want to design a step up converter using lm2577with the following requirements:
VinMin = 3.7
VinMax= 4.6V
Vout = 5.5 V
Iout=1A;
Following the datasheet I made the following calculations:
Ioutmax = 2.1 x 3.7 /5.5V =1.41 A wich is more than my 1A
D= (5.5 + 0.5 - 3.7) /(5.5+0.5-0.6) = 0.41 < 0.85 so I go to step C (reading the datasheet).
I Selected Inductor at minimum 47uH in table 2 so I go for Rc calculation:
Rc = 750 * 1.55 *5,5*5,5 /(3.7*3.7) = 2568 ohm that is a good value
but if I calculate the Cout value I have some problems:
cout >= (0.19 * 47 uh * 2568 * 1.41)/ (3.7*5,5)= 1496 uF =1557uF
and
Cout >= 3.7 * 2000* 21.09 /(487,8 * 5 * 5 *5 )= about 2.5F to big in my opinion
so If I choose the max (as datasheet suggest ) I should use 2.5F for Cout in order to have it working.
What I'm doing wrong? Could you suggest the value of the external components in order to design this kind of boost DC-DC?
Awaitng your kind reply
Thanks a lot
nico