TPS5420

Hi Tom,

I am assuming that you are getting a phase margin violation when you enter your specs (Vin_min=15V, Vin_max=31V, Vout=12V, Iout=1A):

Error building the design. The Designer could not successfully build an  error  free design with this device and these inputs.
Error: Phase margin for this design, 0 deg, is lower than 30˚! Low Phase Warning!
Design Halted.

To increase your phase margin you will need a smaller inductor. To get a smaller inductor, you will need to allow SwitcherPro to consider solutions with a greater output ripple.

You can do this design in the "Advanced Inputs" wizard:

1) In the "Create New Design" dialog, please click on the "Advanced Inputs" tab.
2) Please enter you specs (Vin_min=15V, Vin_max=31V, Vout=12V, Iout=1A) in the appropriate fields.
3) Please click "Find Devices" button.
4) Please select the TPS5420.
5) Please enter 400mV in the "Vo Ripple (1 - 1000 mV)" field.
6) Press "Design Now".

You should get the following:



Now, if you go into the Analysis tab, you will see that the calculated output ripple is 5mVp-p:




I don't know why SwitcherPro requires the user to enter 400mV as the allowed max output ripple in order to generate a design with a 5 mV  output ripple.  I need to follow up on that further.

Regards,
Michael

-- 
Michael Krasnicki
Analog eLab
Texas Instruments