I am designing a Dc Dc converter with LM2840 that needs to have 12 V at the output (0.1A max).
I prepare a prototype (like figure 4 of the datasheet) with the Y version of the IC for reduce inductor space. I have change the inductor value to 15uH and the Cboost to 0.47uF.
I have 2 problems,
With no load, at startup, the regulatod do not stays in an steady state, I tried to drive CB pin with a diode from the output (as Figure 5 from the LM2738 datasheet) and I get the regulation. However, I wonder is that is alowable.
The second problem that I have is that, as a requirement, I need to have aroound 12 V (it could be 11V) at the output for 12V at the input. I red in http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/46622/164535.aspx#164535 that when Vin <Vo, the buck converter stops switching, turns on the FET so that Vo=Vin - Iload*Rds(fet) but the there is some kind of problem because I can't get a steady output.
Any help will be apreciated.