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 100µF. Choose a standard value for RCOMP of 7.87kΩ.
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. Use Equation 45 to calculate the CCOMP value. Choose a standard
value for CCOMP of 3.3nF.
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 to create a pole at the
ESR zero and to attenuate high-frequency noise at COMP using Equation 46. CBW is the bandwidth-limiting capacitance of the
error amplifier. CHF can not be significant enough to be necessary in
some designs. For this design, select a standard value for CHF of
10pF.
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 designs, industry trends, and insights for
designing and managing power supplies, see also TI's
technical
articles.