Design of Current mode boost converter using MCP1630

kirous

New member
I was trying to design a current mode boost converter in CCM using a MCP1630 from microchip with the following design requirements:

*Vinmin=2.7V (minimum input voltage).
*Vinmax=4.2V (maximum input voltage).
*Vout=5V (Output voltage).
*Iout=5A (Maximum output current).
*RL=5 Ohm (load resistor Vout/Iout).

To meet these design specifications, I have calculated the components and they are as follow:

*Dmin=0.16 (Minimum duty cycle)
*Dmax=0.46 (Maximum duty cycle)
*L=5uH (Inductor value)
*Ipeak=2.2A (Peak current)
*C=200uF (Output capacitor)
*Fc=8kH (Crossover frequency).

The sense resistor is selected to be Rs=0.36 ohm, because the maximum current sense signal for MCP1630 is 0.9V (for Ipeak=2.2A Vsense=Ipeak*Rs=0.36*2.2=0.8v, we let 0.1V as a margin).

For the feedback control I have sellected a type 2 amplifier, I have used K-factor method to calculate the components, so the found values are given bellow:

*Divider network: Rup=Rlow=10k
*Refrence voltage Vref=2.5V
*C1=2.5nF
*C2=15.6pF
*R2=100k
I have attached the circuit designed in proteus 8 for clarifications

My question is:

Unfortunatly, when I simulated my circuit, I never get 5V at the output, instead I get 3.94 and the duty cycle approaches 90% and I don't know what is the reason for that failure. Please try to figure out where I have mistaken!!
 

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