SLUSFZ0 November 2024 UCC33411-Q1
ADVANCE INFORMATION
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The UCC33411-Q1 uses hysteritic control to regulate the output voltage between upper and lower bands as shown in Figure 7-4. The regulation block on the secondary side senses the regulated output voltage and sends a feedback signal to the primary side through the inductive communication channel to turn the primary power stage On or Off to maintain the regulated output whithin the hysterisis bands. During steady-state regulation, the burst frequency will change according to the output capacitors and loading conditions. The burst frequency will be highest at higher loading conditions and lowest at light loading conditions by which light load efficiency improvments can be achieved. The Burst-On duration (tON) will increase with heavy loading conditions recommended operating conditions or higher output capacitor values . The UCC33411-Q1 has an overpower protection feature that will limit the maximum tON value to typical of 13us.
The UCC33411-Q1 can program the VCC_REG voltage accoring to the SEL pin connection. The SEL pin voltage is monitored during soft-start sequence when VCC < VVCC_UVLO threshold . The output voltage is then programmed to 3.3V with SEL = VCC or 3.7V with SEL = GNDS. Note that after this initial monitoring, the SEL pin no longer affects the VCC output level. In order to change the output mode selection, either the EN/FLT pin must be toggled or the VINP power supply must be cycled off and back on.