Hi there,
We are trying to implement true shutdown by adding PMOS on Vout referring to TI docs that written by @ Alan Martin, and I have some questions.
1.If PMOS is inserted before feedback resistors as following sch’s second circuit, when the IC is just enabled(at very beginning time), the PMOS breaks the feedback loop, and the PMOS will keep OFF until its source pin voltage is higher that Vin. So I am not sure whether the startup process will be affected,because the PMOS is involved in regulation control loop. I prefer the PMOS be added after feedback resistors as SCH in PPT "Boost Converter Design Tips".
2. Is there any restriction to feedback resistor value selection? I noticed that in datasheet example(section 8.2.26), there is a "92uA current through divider resistors" , how should we interpret this "92uA"? If we use larger resistors, as following SCH, to boost 12V to 24V, will these resistor values be ok? Normal load current is small, about 20mA.
Thanks.