LTC3111 Boost

Hi,

Your schematics mentions the input voltage for the design as 5V. Since it is in the boost mode from 5V in to 7V out, load current of 0.7A might not be guaranteed. However in the circuit there also seems to be loop instability. Have you followed the datasheet to select components and design feedback loop compensation? The compensation values seems to be taken from one of the examples of the application circuit in the datasheet but the inductor and output capacitors are different from the application circuit. So, the power stage and total loop gain might not be correctly designed and that might be leading to instability. Also while selecting the output cap consider the DC biasing effect. The capacitance mentioned in the application circuits of the datasheets are the effective capacitance value after considering DC bias.

Thanks

What values should be changed in order to achieve a stable system?

Thanks

Hi,

You can check your application circuit that inductor and capacitor values are selected as per the datasheet and compensation of the voltage loop has been correctly done as mentioned in the datasheet.

You can also use the application circuits for 5V output on Page 26 and change the resistance R2 value on FB pin for 7V out. Later you can tune or  recalculate the voltage loop for your desired bandwidth if the circuit is no longer unstable. Also am assuming that the layout is good as per the PCB layout guidelines and parasitics on your board are not causing any additional instability. 

The demo board DC1999A of LTC3111 should be a good reference to check the PCB layout. We have all the reference files of demo board in our website. If you want you can also use the board to test your design. 

Thanks

Hi,

You can check your application circuit that inductor and capacitor values are selected as per the datasheet and compensation of the voltage loop has been correctly done as mentioned in the datasheet.

You can also use the application circuits for 5V output on Page 26 and change the resistance R2 value on FB pin for 7V out. Later you can tune or  recalculate the voltage loop for your desired bandwidth if the circuit is no longer unstable. Also am assuming that the layout is good as per the PCB layout guidelines and parasitics on your board are not causing any additional instability. 

The demo board DC1999A of LTC3111 should be a good reference to check the PCB layout. We have all the reference files of demo board in our website. If you want you can also use the board to test your design. 

Thanks