Other Parts Discussed in Thread: TPS561208
Hello,
I am working on a design that need to have a live variable output step-down converter. I need a good power efficiency, so I don't want to use a LDO.
My parameters are :
1. Vin = 12V,
2. Io will vary from 40mA to 200mA
3. Vo will vary from 0.8V to 5.6V
4. The load will be static
5. The Vo will vary to keep the I in the load constant.
I would like to get some advice for this design. It seems to be unusual to do this kind circuit with a buck converter. But, tell me if I am wrong, if I use bigger component value than needed, it should do the trick ?
Since I am new in this, where to start the design ?
In fact, in the past, I already tried a similar project, that I have stopped because of the failure of it and lack of time. I was not using a TI part for the controller. The problem was the output stability (as if the PWM skipped some periods) and the noise output that was too much high (40mV and up) and I was seeing the pwm pulse at the output.
For the new design, I plan to do the following :
1. Select a input capacitor ripple = 5mV
2. Select a output capacitor ripple = 5mV
3. Select the Inductor using the inductor ripple current.
4. Select the output capacitor
5. Try the design and add a second filtering stage.
So, here is my question : How to decide a correct inductor ripple current (is there any starting point values ?) ? And do I have to design for the worst case scenario ? In my case, use 300mA at 7V to select the components?
What about the output ripple? Can I dream to get say, 100uV ?
And finally, does the LMR14206 is the right controller for my need ? The pcb I plan to use is quite small, 1" x 3/4".
Thank you
