I am using the TPS56221 in a 16A switcher application. Using SwitcherPro it comes up with a 1.82K ILIM resistor, which when I calculate the OCP threshold based on Eq. 2 in the datasheet gives a value of 15.4A. Setting my OCP to 20% above my 16A limit or 19.2A for inrush at power-up, I come up with a value of 2.2K. How does SwitcherPro calculate this resistor?
Thanks for submitting this problem. We will take a closer look and get back to you very soon.
We are using equation 2 of datasheet in SwitcherPro to calculate the value of ILIM resistor, which uses Ip-p. Ip-p is a function of VInMax, VOut, IOut and Fsw. In order to debug your issue, could you please provide these inputs? Also, could you let us know if you modified the default design which came up in SwitcherPro with your inputs?
I recall that I did modify the design to increase the input capacitance from 100uF to 330uF to reduce the input ripple and change the inductor for a smaller PCB footprint. These are my design parameters:
Vin: 11V to 13V
Thank you for providing the inputs. We verified the design with your inputs.
Changing the inductor (which changes Ip-p) should actually recalculate the value of Rlim. This is a bug in SwitcherPro because of which Rlim is not being recalculated when the inductor is changed in a TPS56221 design. For now, please calculate the value manually using the datasheet equation 2.
We will add this to the list of bugs to be fixed.
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