7.4 Device Functional Modes
According to the input voltage, the VDD voltage, and the output load conditions, the device can operate in different modes:
- At start-up, when VDD is less than the VVDD(on) turn-on threshold, the HV internal current source is on and charging the VDD capacitor at a (IHV – ISTART) rate.
- When VDD exceeds VVDD(on), the HV source is turned Off and the device starts switching to deliver power to the converter output. Depending on the load conditions, the converter operates in CC mode or CV mode.
- CC mode means that the converter keeps the output current constant. When the output voltage is below the regulation level, the converter operates in CC mode to restore the output to the regulation voltage.
- CV mode means that the converter keeps the output voltage constant. When the load current is less than the current limit level, the converter operates in CV mode to keep the output voltage at the regulation level over the full load and input line ranges.
- When operating in CV or CC mode where IPP is greater than 0.55 X IPP(max), the UCC28730 operates continuously in the run state. In this state, the VDD bias current is always at IRUN plus the average gate-drive current.
- When operating in CV mode where IPP is less than 0.55 X IPP(max), the UCC28730 operates in the Wait state between switching cycles and in the run state during a switching cycle. In the Wait state, the VDD bias current is reduced to IWAIT after each switching cycle to improve efficiency at light loads.
- The device operation can be stopped by the events listed below:
- If VDD drops below the VVDD(off) threshold, the device stops switching, its bias current consumption is lowered to ISTART and the internal HV current source is turned on until VDD rises above the VVDD(on) threshold. The device then resumes switching.
- If a fault condition is detected, the device stops switching and its bias current consumption is lowered to IFAULT. This current level slowly the discharges VDD to VVDD(off) where the bias current changes from IFAULT to ISTART and the internal HV current source is turned on until VDD rises above the VVDD(on) threshold.
- If a fault condition persists, the operation sequence described above in (2) repeats until the fault condition or the input voltage is removed.