SNVSBJ0A December 2019 – June 2020 LM5170
Assuming the output impedance of the gm amplifier is RGM, the gain from the inductor to the output of gm amplifier is determined by Equation 25:
Because RGM is > 5 MegΩ, and the frequency range for loop compensation is usually above a few kHz, the effects of RGM on the loop gain in the interested frequency range becomes negligible. Therefore, substituting Equation 28 into Equation 25, and neglecting RGM, one can get the following:
The total open-loop gain of the inner current loop is the product of H(s) and G(s):
The poles and zeros of the total loop transfer function are determined by:
To tailor the total inner current loop gain to cross over at fCO, select the components of the compensation network according to the following guidelines, then fine tune the network for optimal loop performance.
Therefore, the compensation components can be derived from the above equations, as shown in Equation 36.