Choose compensation components for a stable
control loop using the procedure outlined as follows:
- Based on a specified loop gain crossover
frequency, fC, of 55kHz, use Equation 44 to calculate RCOMP, assuming an effective output
capacitance of 100 µF. Choose a standard value for RCOMP of 20.5kΩ.
Equation 44.
- To provide adequate phase
boost at crossover while also allowing a fast settling time during a load or
line transient, select CCOMP to place a zero at the higher of (1) one
tenth of the crossover frequency, or (2) the load pole. Calculate the necessary
value using Equation 45 and choose a standard value for CCOMP of 1.5nF.
Equation 45.
Such a low capacitance value also helps to avoid output voltage overshoot
when recovering from dropout (when the input voltage is less than the output
voltage setpoint and VCOMP is railed high).
- Calculate CHF using Equation 46 to create a pole at the ESR zero and to attenuate
high-frequency noise at COMP. CBW (31pF) is the bandwidth-limiting
capacitance of the error amplifier. CHF can not be significant enough
to be necessary in some designs. In this design, the high frequency capacitor is
not necessary.
Equation 46.
Note: Set a fast loop with high RCOMP and
low CCOMP values to improve the response when recovering from operation
in dropout.
Note: For technical solutions, industry trends, and insights for
designing and managing power supplies, see also TI's
technical
articles.