Choose compensation components for a stable control loop using the procedure outlined as follows.
- Based on a specified loop gain crossover
frequency, fC, of 40kHz, use Equation 42 to calculate
RCOMP, assuming an effective output capacitance of 82µF. Choose a standard
value for RCOMP of 5.36kΩ.
Equation 42.
- 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. Choose a standard value for CCOMP of 6.8nF.
Equation 43.
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. CBW is the
bandwidth-limiting capacitance of the error amplifier. Select a standard value for
CHF of 47pF.
Equation 44.
Note: Set a fast loop with high RCOMP and low CCOMP values to improve the response when recovering from operation in dropout.