The TPS65262-2 incorporates a peak current mode control scheme. The error amplifier is a transconductance amplifier with a gain of 300 µS. A typical type II compensation circuit adequately delivers a phase margin between 60° to 90°. Cb adds a high-frequency pole to attenuate high frequency noise when needed. To calculate the external compensation components, follow the following steps.
- Switching frequency ƒsw 600 kHz is appropriate for application depending on L and C sizes, output ripple, EMI, and so forth, also gives best trade-off between performance and cost.
- Set up crossover frequency, ƒc, which is typically between 1/5 and 1/20 of ƒsw.
- RC can be determined by
Equation 16. Where Gm_EA is the error amplifier gain (300 µS), Gm_PS is the power stage voltage to current conversion gain (7.4 A/V).
- Calculate CC by placing a compensation zero at or before the dominant pole
Equation 17. - Optional Cb can be used to cancel the zero from the ESR associated with CO.
Equation 18. - Type III compensation can be implemented with the addition of one capacitor, C1. This allows for slightly higher loop bandwidths and higher phase margins. If used, C1 is calculated from Equation 19.
Equation 19.