Vout

VDD

VG

VS

VD

REG

VVDD

VREG

VVDD

VREG

VON

VOFF

SR Control Enable

VREG

VREG

12

UCC24612

SLUSCM5A – AUGUST 2017 – REVISED FEBRUARY 2018

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Feature Description (continued)

Figure 14. Timing Diagram for VDD and REG in Low-side SR Configuration

In some applications, such as USB chargers, the converter is required to deliver the full output current when the

output is over loaded and output voltage drops below the regulation level. In 5-V applications, the output voltage

could drop too low to adequately turn on the SR. In this case, the UCC24612 can be powered through a simple

external R-C-D circuit, as shown in Figure 15. Due to the wide voltage range handling capability, this simple

circuit provides power from the SR drain voltage. Even though this method easily powers up the device, this is a

very inefficient way of powering the controller. A more efficient way would be to use an auxiliary winding to

provide the power.

Figure 15. UCC24612 Used in Low-side and Low Output Voltage Condition

The same biasing method can also maintain the SR controller operation in high-side SR configuration, as shown

in Figure 16. More details about biasing UCC24612 can be found in Power Supply Recommendations.