ZHCSBB4B July 2013 – June 2017 TPS61197
PRODUCTION DATA.
The COMP pin on the TPS61197 is used for external compensation, allowing the loop response to be optimized for each application. The COMP pin is the output of the internal trans-conductance amplifier. The external resistor R8, along with ceramic capacitors C6 (see Figure 18), are connected to the COMP pin to provide poles and zero. The pole and zero, along with the inherent pole and zero in a peak current mode control boost converter, determine the closed loop frequency response. This is important to converter stability and transient response.
The first step is to calculate the pole and the right half plane zero of the peak current mode boost converter by Equation 11 and Equation 12.
To make the loop stable, the loop must have sufficient phase margin at the crossover frequency where the loop gain is 1. To avoid the effect of the right half plane zero on the loop stability, choose the crossover frequency fCO less than 1/5 of the fZRHP. Then calculate the compensation components by Equation 13 and Equation 14.
where
where
If the output capacitor is the electrolytic capacitor which may have large ESR, a capacitor is required at the COMP pin or at the OVP pin to cancel the inherent zero of the output capacitor.