The dynamic phase shedding (DPS) feature allows the controller to dynamically select the number of operational phases for each channel, based on the total output current. This increases the total converter efficiency by reducing unnecessary switching losses when the output current is low enough to be supported by a fewer number of phases, than are available in hardware. Use the PHASE_SHED_CONFIG command to configure the phase adding/shedding thresholds. Refer to the Technical Reference Manual for a full listing of available thresholds.

Set the DPS_EN bit to 0b to disable phase shedding operation. The MIN_PH setting determines the minimum number of phases which are active during light-load operation.

Phase adding is detected based on the summed peak current of all phases in the analog domain. Phase shedding is detected based on average current telemetry, with a forced delay of 120 μs. The phase add thresholds are not affected by current measurement calibration, but the phase shed thresholds are.

Each phase has 3 settings available:

• Phase add threshold (PH_ADDx) selects the nominal phase adding threshold. Set this value approximately equal to the peak efficiency point per phase to optimize overall converter efficiency.
• Phase add hysteresis (DPA_HYSTx) selects the phase add threshold hsyteresis. Nominally set this value to one-half the value of the ripple current on the I_SUM current for that number of phases.
• Phase drop hysteresis (DPS_HYST) selects the phase drop hysteresis (per-phase average current). There is one setting per channel.

The phase add/drop thresholds can be calculated according to the equations below. First determine the ripple cancellation effect for each combination of phase numbers, for the chosen duty cycle using Equation 26. This value affects the true add thresholds.

where

• K_i is the ripple cancellation ratio before the phase transition
• ΔI_ripple(ISUM) is the ripple in the summed current after cancellation
• ΔI_{ripple(IPHASE)} is the ripple each individual phase
• N_i is the number of phases currently active
• D is the converter duty cycle, nominally Vout / Vin
• m is the maximum integer which does not exceed N_i × D (can be zero)

Calculate the DC phase adding thresholds based on the chosen configuration using Equation 27. Phases are added based on peak I_SUM current, after being passed through a 1 μs filter. Typically, choose the DPA_HYST settings to cancel out the current ripple term. Then the DC current adding threshold is equal to the PH_ADDx value selected.

where

• I_{DPA(i to i+1)} is the DC current at which the controller transitions from i to i+1 phases
• PH_ADD_i is the selected phase add threshold for phase number i
• DPA_HYST_i is the selected phase add hysteresis for phase number i
• ΔI_{RIPPLE(PHASE)} is the ripple each individual phase

Calculate the DC phase drop thresholds based on the chosen configuration using Equation 28 phases are added based on the output current telemetry value, with a deglitch filter of 130 μs.

where

• I_{DPS(i+1 to i)} is the DC current at which the controller transitions from i+1 to i phases
• PH_ADD_i+1 is the selected phase add threshold for phase number i+1
• N_i is the number of phases currently active before the phase shed event
• DPA_HYST_i is the selected phase shed hysteresis

Phase add/shed example: 600-kHz, 7-phase, 12-V to 0.8-V converter, with 120 nH inductor

Assume V_IN = 12 V, V_OUT = 0.88, f_SW = 600 kHz, L = 120 nH.

The example below explains how to calculate the phase adding and shedding thresholds for 2 to 3 phases. First calculate the inductor ripple current in one phase. Set the DPA_HYST3 setting to approximately 1/2 the inductor current ripple in one phase. Assuming the phase adding threshold for phase 3, PH_ADD3, parameter is set to 40.0 A, and the phase shed hysteresis, DPS_HYST is set to 2.0 A, the phase adding and shedding thresholds are calculated as shown below.