Figure 7-21 shows a conceptual block diagram of the DCAP+ off-time control loop. Transient response tuning is accomplished by changing the parameters which generate the V_COMP signal. These parameters are accessible using the COMPENSATION_CONFIG command. Refer to the Technical Reference Manual for a register map of this command.

The V_COMP signal is generated by the sum of three signal paths. Finally the V_COMP signal is scaled by the AC gain parameter, K_AC.

• Proportional path: An error amplifier subtracts the sensed output voltage from the output voltage target, set by V_DAC. The gain of the proportional path is set by the AC load line (ACLL). Reducing the value of the AC load line increases the proportional path gain, which gives faster transient response. Setting the AC load line to a very low value can lead to low phase margin.
• Integral path: The difference between the sensed output voltage and the output voltage target, V_DAC, is compared to the ideal droop (I_SUM × DCLL) value to create an error voltage, V_ERR. An integrator adjusts the setpoint of V_COMP, to drive the output voltage error to zero. Integration provides high DC gain, giving the power supply excellent output regulation and DC load line performance. The programmable integration time constant, τ_INT changes the settling time of of the output voltage folliowing a transient. Increasing the integration time constant improves phase margin. The programmable integration path gain, K_INT, sets the gain of the integral path.
• Current feedback: The summed phase current, I_SUM, with a nominal gain of 5 mV/A, is used directly to generate V_COMP, as well as in the integral path to set the DC load line. The gain of this path is not affected by the IOUT_CAL_GAIN or IOUT_CAL_OFFSET calibration commands.

Figure 7-21 Loop compensation conceptual block diagram