JAJSMZ6 december 2021 UCC28781
PRODUCTION DATA
The dead-time optimizer in Figure 7-21 controls the two dead-times: the dead-time between PWMH falling edge and PWML rising edge (tZ), as well as the dead-time between PWML falling edge and PWMH rising edge (tD(PWML-H)).
The adaptive control law for tZ utilizes the line feed-forward signal to extend tZ as VBULK reduces, as shown in Figure 7-23. The VS pin senses VBULK through the auxiliary winding voltage (VAUX) when the primary side switch (QL) is on. The auxiliary winding creates a line-sensing current (IVSL) out of the VS pin flowing through the upper resistor of the voltage divider on VS pin (RVS1). Minimum tZ (tZ(MIN)) is set at VBULK(MAX) through the RTZ pin. When IVSL is lower than 666 μA, tZ linearly increases and the maximum tZ extension is 140% of tZ(MIN).
The control law for tD(PWML-H) is adaptive with the slope variation of the switching node voltage, regardless of the SET-pin voltage as shown in Figure 7-24.