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Before powering up the design board, the first step is to thoroughly review the design to make sure all design parameters are calculated properly. The Excel Design Calculator is a helpful tools to check the accuracy of the design. It is recommended to do a visual inspection to check for the following:
After visual inspection, the user can also use a multimeter to check the solder, Multimeter locked to diode location, Red probe connected to IC ground, Black probe connected to each pin. There should be a ~0.5 V-0.7 V voltage presents on the multimeter, if not, check solder of this pin. Figure 1-1 demonstrates probing UCC28782 Pins with a digital multimeter.
When the solder inspection is complete, the board can input a low voltage, next steps are input short-circuit investigation / HV start circuits operation check / CS pin fault detection and input brown in voltage (startup voltage) detection:
UCC28782 contains six modes of operation that summarized in UCC28782 data sheet Table 8-1. From no load to full load, the operation modes include Survival Mode, SBP2(Second StandBy Power Mode), SBP1, (First StandBy Power Mode) LPM (Low Power Mode), ABM (Adaptive Burst Mode), AAM (Adaptive Amplitude Modulation), The survival mode only kicks in when VDD voltage lower than the 13-V survival mode threshold and also performs the clamping capacitor balancing function to reduce the voltage stress of the secondary side rectifier. Typically, the system does not enter survival mode during regular load change, such as smooth load increase and decrease. The survival mode might kick in at a large output load remove, overshoot on output results in controller stop switching in a long time, then the VDD voltage might drop to touch the 13-V survival mode threshold. The following waveforms show each mode operation (no load to full load).
At no load or very light load, PWMH is disabled and there are four PWML pulses in each burst packet. The peak current of each pulse is programmable through the resistance from IPC pin to ground. See Figure 2-1.