The current error integrator adjusts the modulator control voltage to match the sensed inductor current, Isns, to the current voltage at the VSHARE pin. The integrator is tuned through the GMI, RVI, CZI, CPI, and CZI_MUL parameters in (B1h) USER_DATA_01 (COMPENSATION_CONFIG). Thanks to the natural integration of the 1/f function of the current control gain, the bandwidth of the current control loop can be adjusted with the mid-band gain of the integrator, GMI × RVI.

The current loop crossover occurs at the frequency when the full loop gain is equal to 1 according to Equation 3:

Equation 3.

Solving for the mid-band gain of the current loop, you find Equation 4:

Equation 4.

While Nyquist Theorem suggests that a bandwidth of ½ f_SW is possible, inductor tolerances and phase delays in the current sense, modulator, and H-bridge power FETs make f_SW/4 a more practical target, which simplifies the target current loop midband gain to achieve a current loop bandwidth of f_SW/4 to Equation 5:

Equation 5.

An integrator from DC to the low-frequency zero, RVI × CZI, compensates for the valley voltage of the modulator ramp and the nominal offset of the output voltage. A high-frequency filter pole, RVI × CPI between half the switching frequency and the switching frequency reduces high-frequency noise from VSHARE and minimizes pulse-width jitter.

To avoid loop interactions, the integrating zero frequency must be below the voltage loop cross-over frequency, while the high-frequency pole must be between ½ the switching frequency and the switching frequency to limit high-frequency noise and jitter in the current loop without imposing additional phase loss in the voltage loop.

The closed loop average current mode control allows the current sense amplifier, on-time modulator, H-bridge power FETs, and inductor to operate as a transconductance amplifier with forward gain of 1/CSA or 162.5 A/V with a bandwidth equal to F_coi.