Could someone tell me how to externally add phase compensation to the TPS62148?
I am seeing a design case where an FRA(frequency response analyzer) is used to apply a sine wave to the FB pin, and the phase margin is only 30deg when gain hits 0dB.
-Darren
Hello Darren,
One way to increase the phase margin for this device is by adding an external feedforward capacitor between the Vout and FB pins. It adds a pole and zero to the control loop to boost phase margin. Cff is calculated from the equation:
where fco is the crossover frequency measured by the FRA, and R1 and R2 are the feedback resistors.
Another method would be to take advantage of the built-in (internal) 25pF feedforward capacitor by choosing values for R1 and R2 to place the zero and pole. This would eliminate having to add another (external) capacitor.
More detailed information on implementing feedforward capacitors can be found from this App Note.
Let me know if this answers your question.
Thanks,
Joseph
