Hello,
I have been working on Lm3478 as a sepic. I have fixed input of 25V but I needed the same circuit to generate either 18V or 46V depending on the load I connected. The output current draw would be 0.7A in both cases.
I have followed all the design rules accurately to size my power components but my circuit is unstable. It is the right hand zero which is causing me trouble. I used app note 1484 for designing my compensation. The app note doesn't specify what gain I add to the my transfer function.
I have used app note 1286 for designing compensation when I used this device as a boost controller in the past and that note is exhaustive. It provides all the information I need to build a transfer function and actually simulate the loop in MATLAB to see what gain crossover frequency and phase margin I have.
Is there any any app note for the sepic configuration that provides enough info for building a transfer function and seeing where I am going wrong.
Circuit info:
Vin = 25V
Vout=47V
Io=0.7A
fs=350 kHz
L1=94uH
L2=100uH
Cout = 4x4700 uF
Isolation capacitor = 1uF
Rsn=0.01 ohm
(All parameters chosen with power loss and load requirements in mind. I cannot add a schematic due to ITAR reasons but I will try to provide as much info as I can)
Best,
Rohit Joshi
