SLUSCC7C July 2016 – June 2018 TPS546C23
The device uses voltage-mode control with input feedforward. For an in-depth discussion of voltage-mode feedback and control, refer to Under the Hood of Low-Voltage DC/DC Converters (SLUP206). Frequency compensation can be accomplished using standard techniques. TI also provides a compensation calculator tool as part of the WEBENCH® selection simulation services to streamline compensation design. The tool provides the recommended compensation components and approximate bode plots. As a starting point, set the crossover frequency to 1/10 fSW and 2 to 5 times the resonant frequency of the output LC filter. The phase margin at crossover should be greater than 45°. The resulting plots should be reviewed for a few common considerations. The error-amplifier gain should not hit the error amplifier gain bandwidth product (GBWP). The error-amplifier gain at the switching frequency region is recommended to be approximately 6 dB in general. The high-frequency capacitor from the COMP to FB pins for this device must be above a typical value of 100 pF to 150 pF to lower the high-frequency gain for stability. Use the tool to calculate the system bode plot at different loading conditions to ensure that the phase does not drop below zero prior to crossover, as this condition is known as conditional stability.
The design tool provides the compensation network values as a start point. Measuring the real-system bode plot after the design and adjusting the compensation values accordingly is always recommended. Table 15 lists the compensation values from the tool calculation and optimization based on the measured data.
|RESISTOR||VALUE (kΩ)||CAPACITOR||VALUE (pF)|