ZHCSOY9 december 2021 UCC28781
PRODUCTION DATA
When fBUR is below the 8.5-kHz upper burst frequency threshold (fSBP2(UP)), UCC28781 exits SBP1 mode and enters into SBP2 mode. Compared with the SBP1 mode, the pulse count is doubled and VCST can be programmed by the IPC pin. The VCST programmable range in SBP2 is between 0.27 V and 0.4 V. The purpose of SBP2 is to further lower fBUR in order to minimize standby power.
The fBUR condition to trigger the mode transition from SBP2 to SBP1 depends on the IPC pin voltage setting as well. If VIPC is set lower than 0.9 V or the IPC pin is shorted to AGND, VCST is equal to VCST_IPC(MIN), and the mode transition occurs when fBUR is increased above the same 8.5-kHz threshold. On the other hand, if VIPC is set higher than 0.9 V, VCST is higher than 0.27 V, and the mode transition occurs when fBUR is increased above the 1.7-kHz lower burst frequency threshold (fSBP2(LR)). The purpose of skipping the burst frequency range between 1.7 kHz and 8.5 kHz is to avoid the most sensitive audible frequency range to the human ear. The frequency skipping is only enabled, when the peak current is set higher by VIPC > 0.9 V.