7.3.16 Small Signal Model for Frequency Compensation

The device uses a transconductance amplifier for the error amplifier and readily supports two of the commonly used frequency compensation circuits shown in Figure 22. In Type 2A, one additional high-frequency pole is added to attenuate high-frequency noise.

The following design guidelines are provided for advanced users who prefer to compensate using the general method. The step-by-step design procedure described in Detailed Design Procedure may also be used.

Figure 22. Types of Frequency Compensation

The general design guidelines for device loop compensation are as follows:

1. Determine the crossover frequency f_co. A good starting point is one-tenth of the switching frequency, ƒ_SW.
2. R₃ can be determined by:
Equation 10.

where gm_ea is the gm of the error amplifier (1400 μS), gm_ps is the gm of the power stage (22 S) and VREF is the reference voltage (0.804 V).

3. Place a compensation zero at the dominant pole using C₁ and R₃.
   C₁ can be determined by
Equation 11.
4. C₂ is optional. It can be used to cancel the zero from the equivalent series resistance (ESR) of the output capacitor C_OUT.
Equation 12.