SLUAAG2 October 2021 UCC28782

2 Control Law across Entire Load Range

UCC28782 contains six modes of operation summarized in Table 2-1. Starting from heavier load, the AAM mode forces PWML and PWMH into complementary switching with ZVS tuning enabled. ABM mode generates a group of PWML and PWMH pulses as a burst packet, and adjusts the burst off-time to regulate the output voltage. At the same time, the burst frequency variation is confined above 20kHz by adjusting the number of PWML and PWMH pulses per packet to mitigate audible noise and reduce burst output ripple. In LPM, SBP1, and SBP2 modes, PWMH and the ZVS tuning loop are disabled, so the converter operates in valley-switching. The survival mode is to maintain V_VDD higher than V_VDD(OFF) in a long burst off time, and also performs the clamping capacitor balancing function to reduce the voltage stress of the secondary-side rectifier .

Table 2-1 and Figure 2-1 also show the frequency and power level at each mode, so it helps to understand the mode operation.

Table 2-1 Functional Modes

	MODE	OPERATION	PWMH	ZVS
AAM	Adaptive Amplitude Modulation	ACF operation with PWML and PWMH in complementary switching	Enabled	Yes
ABM	Adaptive Burst Mode	Variable F_BUR > F_BUR(LR), ACF operation in complementary switching	Enabled	Yes
LPM	Low Power Mode	Fix F_BUR ≈ F_LPM, valley-switching	Disabled	No
SBP1	First Standby Power Mode	Variable F_BUR between F_SBP2(LR) and F_SBP2(UP), valley- switching	Disabled	No
SBP2	Second Standby Power Mode	Variable F_BUR< F_SBP2(UP) as V_BUR < 0.9 V; Variable F_BUR< F_SBP2(LR) as V_BUR > 0.9 V; Both are in valley-switching	Disabled	No
INT_STOP	Survival Mode	When V_VDD < V_VDD(OFF) + V_VDD(PCT), a series of PWML pulses followed by a long PWMH pulse is generated	Enabled in the lastswitching cycle of a survival-mode burst packet	No

Figure 2-1 Control Law Over Entire Load Range Based on the V_VS Condition as V_IPC< 0.9 V

Figure 2-2 Control Law Under Different Load Sweep Direction as V_IPC > 0.9 V and V_VS > V_VSLV(UP)