SLVSDA7E February 2017 – August 2019 TPS61178
PRODUCTION DATA.
The TPS61178x uses the fixed frequency peak current mode control; there is an internal adaptive slope compensation to avoid the sub-harmonic oscillation. With the inductor current information sensed, the small-signal model of the power stage reduces from a two-pole system, created by L and C_{OUT}, to a single-pole system, created by R_{OUT }and C_{OUT}. The single-pole system is easily used with the loop compensation. Figure 24 shows the equivalent small signal elements of a boost converter.
The small signal of power stage including the slope compensation is:
where
The single pole of the power stage is:
where
The zero created by the ESR of the output capacitor is:
where
The right-hand plane zero is:
where
Using He(s) to model the inductor current sampling effect as well as the slope compensation effect on the small signal response, is shown in Equation 19
where
where
The slope compensation adaptively changes with the switching frequency and duty cycle.
He(s) models the inductor current sampling effect as well as the slope compensation effect on the small signal response. Note that if Sn > Se, e.g., when L is too small, the converter operates as a voltage mode converter and the above model no longer holds.
The TPS61178x COMP pin is the output of the internal trans-conductance amplifier.
Equation 22 shows the equation for feedback resistor network and the error amplifier.
where
where
where